# Cement board research....



## Gooserider

I've been having an interesting time the last couple days checking out various brands of cement boards, I'm finding they are very much not all alike, and probably should not be considered interchangeable.  Everything that I mention in the following info comes from either the product websites, or the company "tech support" phone line people.

At this point, I would say that the clear winner for hearth use is Durock, with a distant second for Hardibacker.

I would be hesitant to use Wonderboard, and absolutely wouldn't consider Permabase.

*Durock* clearly specifies in it's descriptive product info PDF that it is acceptable for use in "UL Listed Wall shield / Floor Protectors", and gives an R-value for the 1/2" sheets of 0.26. The US Gypsum website describes it as "Non-Combustible" - there seems to be no hesitation about labeling it suitable for hearth applications.

*Hardibacker* has  that states it is "online documentationthat states it is "Non-Combustible per ASTM E 136", and "1 Hour Fire Resistive per NER 405.  It lists an R-value for the 1/4" sheet of 0.13, but gives no value for 1/2".  The FAQ mentions it as suitable for "Fireplace Facing" but makes no mention of use for hearth protection.  When I called their tech support line, they confirmed that Hardiebacker was definitely "Non-combustible" and said it could be used under a hearth, but that heat would "go right through it" and said it was only about R-0.15.  The tech support guy didn't sound really comfortable with the idea of using it for hearth protection.  However it sounds like it would be 100% OK to use in "clearance reduction" wall shields.

*Wonderboard* had online documentation that pretty much made no mention of fire resistance, the only thing I could find was the MSDS line on Fire Hazards that said "Will not burn".  I called their tech support line, and was told that Wonderboard has an R-value of 0.2, but that the fiberglass facing was "combustible" so the product would only be suitable if it was actually covered in a NON-Latex based cement and tile - then it would "probably" be OK, but didn't seem totally comfortable with the notion.

It was an interesting point that he brought up however that it would be a concern about the nature of the cement that was used to put the tiles down with - it needs to be non-combustible, and some formulations contain latex that is.

*Permabase* in their documentation says it can be used for "fire resistant walls" but lists expanded polystyrene in it's ingredients on the label, and has a statement in their online documentation that the product should not be exposed to temps over 220*F (105*C).  It was listed with an R-value of 0.2, but their tech support line person said it was "combustible" because of the expanded polystyrene (aka styrofoam) beads in the cement mixture.


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## webbie

I think most of them use fiberglass netting to hold the cement together. We have to keep in mind the specific use. A Hearth Board is meant to lower temperatures from a relatively low temperature to an even lower one....say, 300 degrees to 150 degrees. Therefore, the combustibility of the materials is not as important as the R or K value - since fiberglass is good to at least double or more of the temperature that is likely to be found on a hearth board. Even at a really high temp, the fiberglass would be more likely to deform or melt since it was encapsulated. 

I have seen hearth boards that use other fiber sand sheetrock, neither of which are non-combustible. Some even use wood around the border. As to the latex which is added to or already in thinset mortars, I think the same thing applies. These hearths are not going to hit temperatures of 500+ degrees except perhaps in the most extreme situation when legs are cut off a stove and someone installs it incorrectly.

Personally, I would use Durock if possible, wonderboard as a second choice and stay away from the others. Elk (a building official) is comfortable with Hardi even though it has paper in it (cellulose), but again...that is encapsulated and he has taken a torch to the stuff and it does not burn. In no case would I use the last one mentioned, since their documentation DOES list a max. temp.

Extensive experience in the field seems to indicate that (at least) Durock and Wonderboard are readily available and work well for this purpose.....so why mess with anything else?


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## Corie

Goose,

Although not a cement board (and I realize that was the scope of your study), could you do the same research for the Micore 300?  It seems to be very popular in hearth construction, but I wonder if the manufacturer has the same reservations as those you spoke with.


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## Gooserider

Webmaster said:
			
		

> I think most of them use fiberglass netting to hold the cement together. We have to keep in mind the specific use. A Hearth Board is meant to lower temperatures from a relatively low temperature to an even lower one....say, 300 degrees to 150 degrees. Therefore, the combustibility of the materials is not as important as the R or K value - since fiberglass is good to at least double or more of the temperature that is likely to be found on a hearth board. Even at a really high temp, the fiberglass would be more likely to deform or melt since it was encapsulated.
> 
> I have seen hearth boards that use other fiber sand sheetrock, neither of which are non-combustible. Some even use wood around the border. As to the latex which is added to or already in thinset mortars, I think the same thing applies. These hearths are not going to hit temperatures of 500+ degrees except perhaps in the most extreme situation when legs are cut off a stove and someone installs it incorrectly.
> 
> Personally, I would use Durock if possible, wonderboard as a second choice and stay away from the others. Elk (a building official) is comfortable with Hardi even though it has paper in it (cellulose), but again...that is encapsulated and he has taken a torch to the stuff and it does not burn. In no case would I use the last one mentioned, since their documentation DOES list a max. temp.
> 
> Extensive experience in the field seems to indicate that (at least) Durock and Wonderboard are readily available and work well for this purpose.....so why mess with anything else?



I agree with much of what you say Craig, it makes considerable sense, but I was looking at a combination of what was said and not said...  I'll admit that I didn't call the Durock tech line, but the link I gave didn't make me want to - it answered all my questions and made specific mention of the application.  The others seemed much more hesitant when I talked to their tech support folks, which I did because I couldn't find the answers in the online documentation.  Once I had the person on the line, I was listening to not only what they had to say, but how "comfortable" they seemed in saying it.  Wonderboard seemed like they were OK, but only if you covered their fiberglass.  Hardiebacker was totally emphatic that they were NON-combustible, but seemed concerned about their insulating value...

I actually got started on this because of availability - the Home Despot that I went to had Wonderboard and Hardi-backer, but did NOT carry Durock.  The Permabase looked like a reasonable substitute, and the aprons said it was what they had switched to instead of Durock, so I purchased two sheets - now I have to find another place to use them...



			
				Corie said:
			
		

> Although not a cement board (and I realize that was the scope of your study), could you do the same research for the Micore 300?  It seems to be very popular in hearth construction, but I wonder if the manufacturer has the same reservations as those you spoke with.


I might at some point, but I'm currently trying to deal with a backlog of projects, a bunch of which are sort of time sensitive, so this would be fairly far down the stack...

Gooserider


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## jtp10181

I read on the Hardi site someplace that they recommended NOT using their product for fireplaces. I think it was in the FAQ section.


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## Gooserider

jtp10181 said:
			
		

> I read on the Hardi site someplace that they recommended NOT using their product for fireplaces. I think it was in the FAQ section.



From the Hardiebacker FAQ section...



> Q. Can I use HardieBacker board as a fireplace facing?
> A: Yes, HardieBacker board can be used as a fireplace facing. HardieBacker 1/4'' board can be used as a component in a 1-hour fire resistive construction when installed in compliance with National Evaluation Report NER-405. HardieBacker boards are recognized as non-combustible, when tested according to ASTM E 136.



Looks to me like they think it's OK...  It doesn't mention using it in clearance reduction shields, but I would think if you can use it for facing, and they tell you it's non-combustible....

Gooserider


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## jtp10181

Wow thier site has some nice info on it...

http://www.jameshardie.com/dealer/fire_faq.shtml

_Can James Hardie products be used around a fireplace?
Because heat will transfer through JH products, they cannot be used around a fireplace._

http://www.jameshardie.com/dealer/helpSupport_faqs.shtml

_Q. Can I use HardieBacker board as a fireplace facing?
A: Yes, HardieBacker board can be used as a fireplace facing. HardieBacker 1/4'' board can be used as a component in a 1-hour fire resistive construction when installed in compliance with National Evaluation Report NER-405. HardieBacker boards are recognized as non-combustible, when tested according to ASTM E 136._

Hmmmmmm  :question:


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## elkimmeg

Why I support Hardi backed board is ease if use no nasty rough edges smoother surface easier to drill nail and cut than cement board . Till one has used both extensively, it is hard to pass judgment. The wed site do not expound practical experience in applications After a bout 400 squared of hardi siding I feel I have cut and installed enough to place a value judgment

 Hundreds of sheets of tile backer cement board installed, I'll tke hardi backer board anytime. The only reason I suggested hardi backer board is not price it cost more but for a dollar or two the ease of use is worth it.. With keyman as a wittiness I applied my acetylene torch with the cutting edge to the hadri backer product  It did not burn did not smoke and very little blackening I made it cherry red and it still stayed intact.  I doubt any hearth pad will be subjected to the heat of an acetylene cutting torch. Ever work with cement boards it is nasty material to work with


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## Gooserider

I agree, this is interesting - I wonder if someone should call them on it?  I got the same text using 1/4" board (on the 1/2" board FAQ) from the page on the product itself Here....  I do wish they'd make up their minds...

Gooserider


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## Gooserider

elkimmeg said:
			
		

> Why I support Hardi backed board is ease if use no nasty rough edges smoother surface easier to drill nail and cut than cement board . Till one has used both extensively, it is hard to pass judgment. The wed site do not expound practical experience in applications After a bout 400 squared of hardi siding I feel I have cut and installed enough to place a value judgment
> 
> Hundreds of sheets of tile backer cement board installed, I'll tke hardi backer board anytime. The only reason I suggested hardi backer board is not price it cost more but for a dollar or two the ease of use is worth it.. With keyman as a wittiness I applied my acetylene torch with the cutting edge to the hadri backer product  It did not burn did not smoke and very little blackening I made it cherry red and it still stayed intact.  I doubt any hearth pad will be subjected to the heat of an acetylene cutting torch. Ever work with cement boards it is nasty material to work with



Not arguing the ease of use question - If I was putting it in the bathroom it would be easy to choose the Hardiebacker.  But as JTP is pointing out, we have the MANUFACTURER saying that it both is and is NOT approved on their own website. - Where does that leave me as the "inspectee" if I used the stuff in good faith based on the statement I was referencing - and one of your colleagues says "NO" based on the statement that JTP found?  Your test with the torch might be impressive, but does it over-rule a manufacturer saying the product isn't suitable?  


On another topic that is related - my post on it seems to have either dissappeared or didn't get up for some reason - The VC Encore 2550 manual says: 





> For installations with the heat shield attached, use a non-combustible floor protector such as *1/4" non-asbestos mineral board or equivalent*, or 24 gauge sheet metal



I have been trying, w/o much luck to find out EXACTLY what constitutes "1/4" non-asbestos mineral board or equivalent" in terms of either a specific product, or an "R-value" - Do you have a specific reference that would say?

I tried calling VC - they said "Call the dealer" - when I said I didn't have a dealer, they gave me a local reference.

I called the dealer - they said "Call the Building Inspector" - In Billerica the FD handles stove install inspections, so I called the FD

The FD said they didn't have a clue, but what I was planning sounded good - but call the building inspector.

The building inspector said he wasn't sure either, but would buy off on 1/2" Durock if I showed him a web page printout saying it was non-combustible...

I really hate vague manuals.  >:-( 

Gooserider


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## jtp10181

That's about as useful as the Quad manuals that say [3/8" metal clad millboard].

What I take off of the difference in info form their site is that you CAN use the hardibacker as a FACING material backer (because it IS non-combustible).  But, "Because heat will transfer through JH products, they cannot be used around a fireplace [as thermal protection]." Make sense to everyone else?

On a side note, HHT recently started shipping white non-comb sheeting materials with fireplaces that have non-combustible zones around the fireplace. This stuff is pretty hard, easy to screw down, should cut easy, and very non combustible. I don't know if it would offer thermal resistance, and I don't know how available it is. But it is really nice stuff.


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## Gooserider

jtp10181 said:
			
		

> That's about as useful as the Quad manuals that say [3/8" metal clad millboard].
> 
> What I take off of the difference in info form their site is that you CAN use the hardibacker as a FACING material backer (because it IS non-combustible).  But, "Because heat will transfer through JH products, they cannot be used around a fireplace [as thermal protection]." Make sense to everyone else?



Sort of, except that they give an R-0.13 rating to their 1/4" material - I haven't been able to find anything on their 1/2" material, but doubling the 1/4" number gives 0.26, same as 1/2" Durock.  Their tech support guy said around 0.15, but sounded like he really didn't know for certain.  However that is about the same range as Wonderboard, and what was given for Permabase, so I would say that Hardibacker is no worse than any other cement board - thus at least in theory it should work as fire protection if Durock would, either by itself in a low R-value requirement situation, or with Micore, etc. as part of a "sandwich" construction.

It should also be fine as clearance reduction material, since it is non-combustible.  Everything I've read on NFPA specs for clearance reduction shields say that they have to be non-combustible, but don't care about thermal resistance - note that plain sheet metal (effective R-0.0) is a valid material...

Gooserider


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## wg_bent

Goose, I know you have to go with what is called out in the specs here, so take this with grain of sand.

I built my hearth out of Durock.  3 layers to be exact.  screwed together then tiled with a 3" airspace below.  

The top of the hearth get's pretty warm, but the lower pieces (The underside) are never even luke warm.  The heat does not transfer through to the bottom layer.

Also, I use a left over piece of it to block the fire when doing quick cleanup's of the door.  I left it there (attended of course) for about 5 minutes and the fiberglass did turn a little brown, but it was exposed to a rather hot bed of coals.  You can guess what that temp was, but I"m sure it was close to 1000 or more perhaps.  The Durock was awful hot after that, so I covered it with foil, and now I have yet to see that piece get much more than warm. 

The point here is this stuff is VERY tough and fire proof.  The company is being conservative and rightly so, as some yahoo would attempt to build a fireplace out of it if they said it was fireproof.


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## Gooserider

FWIW Department - I just called Hardi tech support again, and spend a fair bit of time trying to show them the problem -  The tech agreed that the Fire Prevention FAQ Reference that said it couldn't be used was poorly worded and needed to be fixed.  

His explanation makes some degree of sense, though Elk can probably clarify a bit better - There are apparently two different types of construction standards - Fire Resistive or Fire Rated, and Non-Combustible.  Hardibacker is "Non-Combustible" so it can be used in "non-combustible" applications, but can't be used in fire-resistive because it transfers heat.  This is consistent with the next question about substituting Hardibacker for Type X fire-rated gypsum, where they say no because they transfer too much heat - Hardibacker is R-0.19 and Gypsum is R-0.45 for the 1/2" product.

Thus bottom line is that it depends on the language in the stove manuals - if they say "Non-Combustible" then Hardibacker can be used, if they say "Fire Resistive" or "Fire Rated" then they can't.

I also got a more definitive answer on the R-value rating - He said their nominal 1/2" product is really only 7/16" thick, which is done to save weight over other cement boards, and has an R-value of 0.19

Gooserider


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## dmt5000

There is a product called Mircore 300 made by USG that has less than one-quarter of the thermal conductivity rating for Wonderboard (or almost five times the r value, that will allow you to make a much thinner hearth board. It seems to be about $75 for a 4x8 sheet. There is another thread somewhere on this site that has a little table that compares the K and R values of a lot of different materials; very useful.


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## Highbeam

The trouble is that micore is not available in many places. I could not source a single sheet in the whole state of WA. Told by USG that I may have a very hard time finding it at all. Good ratings though.


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## dmt5000

Yeah, I had to special order it, but it could be gotten through a local lumberyard (Springfield, MA).


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## Highbeam

I called several and they all thought I was nuts. They knew what sheetrock was, they knew that USG made sheetrock, but they wouldn't source a sheet of some other USG product. I could have bought a pallet at one place. 48" tall pallet-1/2 sheets-96 sheets-75$ per sheet= way too much money. Most people thought I was nuts at the mention of micore. Even the people that make the preman'd stove pads.

But this thread is about the cement boards and I will admit that I used wonderboard from HD which I assumed was an identical product to durock. Every layer of the wonderboard except the very bottom has a healthy coat of thinset mortar on it so the fibergalss stuff is not exposed. The wonderboard cuts like plywood with an abrasive bit on my circular saw. Dusty yes. Easily cut with precision- yes.


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## dmt5000

I wanted to get it because I want as thin a hearth board as possible, and with the Micore K value, I only need 1/2", with clay tiles (which provide almost no insulation) on top, to meet my stove's requirements. I actually could get the necessary value with 1/4" Micore, but I don't believe that it is available. I don't know what the distribution problem is. I checked on the USG site and they listed distributors in Redmond and Spokane, so I don't know what's up with that. They do list stoveboard core as a recommended product usage. I'm not sure why it has such a high K value compared to Wonderboard, etc. Perhaps it is made with air-entrained concrete?


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## Highbeam

"I checked on the USG site and they listed distributors in Redmond and Spokane,"

Exactly. A distributor buys lots and lots of pallets and distributes them. What you need is a retailer. I thought I would be smart and call the distributor to try and find the customers. No dice.


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## Hogwildz

dmt5000 said:
			
		

> I wanted to get it because I want as thin a hearth board as possible, and with the Micore K value, I only need 1/2", with clay tiles (which provide almost no insulation) on top, to meet my stove's requirements. I actually could get the necessary value with 1/4" Micore, but I don't believe that it is available. I don't know what the distribution problem is. I checked on the USG site and they listed distributors in Redmond and Spokane, so I don't know what's up with that. They do list stoveboard core as a recommended product usage. I'm not sure why it has such a high K value compared to Wonderboard, etc. Perhaps it is made with air-entrained concrete?



The Micore 300 I have is not made to have tiles cemented directly to it. If I was you, I would add a 1/4" or Durock to the top. Then you have a cement board to adhere your tiles to.


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## Gooserider

Micore has a much higher R-value because it's a TOTALLY different substance.  Durock, Wonderboard, Hardiebacker, etc. are Cement boards, made with concrete.  Micore is a CERAMIC FIBER product, more akin to fiberglass that has been compressed into a mat.

It's good stuff, hard to find, somewhat expensive, but very useful.  When planning your hearth though, it is worth noting that one should not use it by itself - the stuff is a bit "squishy" and is not suitable as tile underlayment, as tile requires a VERY rigid surface.  Best practice is a layer approach w/ one or more layers of Micore, followed by a layer of cement board with the tile on top of that.

See the Wiki article (which I wrote most of) HERE for more details.

Gooserider


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## KeithO

Try this stuff http://www.unifrax.com/PRIUS07.NSF/ByFormNo/C1210G3/$File/C1210G3.pdf  It is UL recognized for floor protectors.  Will also require cementboard for structural integrity, but vastly reduces heat transfer.  Data page is here: http://www.unifrax.com/web/UnifraxH...FEC07F2962C8450185256C3E0060038A?OpenDocument

They will ship anywhere in the US.   I believe the board material is made in Indiana, even though the sales office is in NY state. (edit) Board over 1" is made in Indiana and less than 1" is made in Tonowanda NY.  And as I have said before, Unifrax is quite a nice company if you're the little guy.  If the Min order qty is a problem, give the folks in NY a call and they may find a smaller qty to get to you.


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## dmt5000

Thanks, Hog and Goose, for the tip on adding a cement board layer for the tile base. No way I would have known about it otherwise.


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## thephotohound

I've used both Hardibacker and Durock. Based on ease of cutting alone, I would never go back to Hardibacker. Durock all the way!


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## dmt5000

How's wonderboard for cutting?


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## Highbeam

Cutting wonderboard was easy in a straight line with an abrasive bit in my circular saw. Cutting holes was pretty easy by drilling smaller holes around the perimeter and then knocking out the center. I then nibbled the perimeter smooth with pliers.

The stuff is heavy though at 96 lbs per 3x5 sheet.


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## Hogwildz

Note on cutting Wonderboard, Permabase, Durock, etc.
If you read the directions sticker stuck to the board. It clearly states not to cut with a saw, grinder, etc. The stuff in there is not good to breathe.
The directions on mine specifically said to cut with a utility knife or similar. Exactly what I did, and worked perfect. And no dust mess, power cords, or power equipment needed. Just score with knife and snap. Pretty much same procedure as cutting drywall. Just a suggestion.


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## Highbeam

Uh oh, I may die soon.


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## Hogwildz

Better you than me


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## nshif

I cut all my hardibacker with a saw, much faster. Just wear a good mask and goggles, the dust will dry out your eyes bad. And hell it cant be any worse then the pack of smokes I take in a day.


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## Gooserider

Wearing mask and goggles it isn't terribly bad to cut the stuff outside.  

According to the documentation on all the cement board brands, the hazard is "respirable silica" in the dust, which is a carcinogen and IIRC was the sort of thing that contributed to the old coal miners "Black Lung" disease - essentially it is a size and material of dust that your body can't eliminate so it gets into your lungs and sits.  As an irritant it can eventually lead to cancer, or it can just clog things up.  I would put it in the class of "a little bit probably won't kill you" but definitely worth doing as much as you can to reduce exposure.

All the boards said to to use the "score and snap" method of cutting if possible.  If not, they reccomended wet saws, and / or saws with dust collection built in, and respirators.

Gooserider


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## Hogwildz

When I was just out of HS, I had a job at Budd trailers. I had my own single bay away from the rest of the shop that I had to sand blast the decals off the sides of semi trailers. I was given a regular painters respirator and a hood. On the side of the bags of sand said" Warning, Silica, prolonged exposure without the use of proper resppirator & equipment may cause lung disease". There was an old painter there had emphasyma (spelling) and conitnued to smoke and paint without a mask.
I can tell you a regular painters respirator was not great. It should have been a self contained mask & air tank.
I would pull that hood off and respirator off and have a mouth for of grit, along with the inside of the mask being caked. I didn't care much then, I was young and a lil dumber than I am nowawdays. I smoke alot, and years of breathing roofing chemicals, tar etc, has me thinking more these days. But yes, I still don't wear anything cept maybe some glasses when sawing wood etc. But I try and work smart most of the time, cut in ventilated areas etc.. Anyone can bust my stones as much as you feel like it. I know I am high risk due to my past work. And when I think of it, I try not to contribute to it. Everyone is all gung ho for personal safety protection when cutting logs & etc. I see no difference here.


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## BrotherBart

Hogwildz said:
			
		

> When I was just out of HS, I had a job at Budd trailers. I had my own single bay away from the rest of the shop that I had to sand blast the decals off the sides of semi trailers. I was given a regular painters respirator and a hood. On the side of the bags of sand said" Warning, Silica, prolonged exposure without the use of proper resppirator & equipment may cause lung disease". There was an old painter there had emphasyma (spelling) and conitnued to smoke and paint without a mask.
> I can tell you a regular painters respirator was not great. It should have been a self contained mask & air tank.
> I would pull that hood off and respirator off and have a mouth for of grit, along with the inside of the mask being caked. I didn't care much then, I was young and a lil dumber than I am nowawdays. I smoke alot, and years of breathing roofing chemicals, tar etc, has me thinking more these days. But yes, I still don't wear anything cept maybe some glasses when sawing wood etc. But I try and work smart most of the time, cut in ventilated areas etc.. Anyone can bust my stones as much as you feel like it. I know I am high risk due to my past work. And when I think of it, I try not to contribute to it. Everyone is all gung ho for personal safety protection when cutting logs & etc. I see no difference here.



Ya want ya some silca, just mess with the furnace cement we talk about here. And as for carcinogens in the lungs nothing beats the stuff flying around when you are cleaning a chimney.

I have a respirator and forever forget it in the rush to get stuff done.


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## Gooserider

Hogwildz said:
			
		

> When I was just out of HS, I had a job at Budd trailers. I had my own single bay away from the rest of the shop that I had to sand blast the decals off the sides of semi trailers. I was given a regular painters respirator and a hood. On the side of the bags of sand said" Warning, Silica, prolonged exposure without the use of proper resppirator & equipment may cause lung disease". There was an old painter there had emphasyma (spelling) and conitnued to smoke and paint without a mask.
> I can tell you a regular painters respirator was not great. It should have been a self contained mask & air tank.
> I would pull that hood off and respirator off and have a mouth for of grit, along with the inside of the mask being caked. I didn't care much then, I was young and a lil dumber than I am nowawdays. I smoke alot, and years of breathing roofing chemicals, tar etc, has me thinking more these days. But yes, I still don't wear anything cept maybe some glasses when sawing wood etc. But I try and work smart most of the time, cut in ventilated areas etc.. Anyone can bust my stones as much as you feel like it. I know I am high risk due to my past work. And when I think of it, I try not to contribute to it. Everyone is all gung ho for personal safety protection when cutting logs & etc. I see no difference here.



Absolutely, I'd tell you to wear the gear, but I understand where you are coming from at the same time - One of my pet gripes is the question of how many injuries are caused by protective gear that gets in the way, causes one to be clumsy, or interferes with vision, etc.  I take a sort of middle ground...  I wear glasses, and I've had a difficult time finding goggles etc. that don't fog up or make my glasses fog up in a minute or two...   Sorry, IMHO if I can't see, I'm not safe...  So when I get glasses, I get BIG lenses, and have them made from hard surface polycarb - but I don't do OSHA specs as they weigh to much for comfort.  I don't usually wear a respirator when doing wood work, but will when I'm emptying out the ashes in the wood stove.  I have gotten more and more into the PPE gear, in part because I've gotten fussier and been able to find stuff that fits better.

The other thing that I feel is a factor is the saying that gets ignored by a lot of people "The dose makes the poison" - There is a lot of difference between an occasional exposure on a small scale, and doing it daily for a living.  I am going to suffer a lot less damage from cutting an occasional peice of plywood or even cement board w/o a respirator than a carpenter that is doing the same thing 40 hours a week...  However the safety people tend not to make that difference...

Gooserider


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## dmt5000

Ddes anyone know anything about USG "Fiber Rock" underlayment, i.e., is it suitable for a tile backer under a wood stove? Thanks,


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## Gooserider

dmt5000 said:
			
		

> Ddes anyone know anything about USG "Fiber Rock" underlayment, i.e., is it suitable for a tile backer under a wood stove? Thanks,



Just looked it up - their Submittal sheet #F102 for it on the 
FibeRock web page says it shouldn't be exposed to sustained temps over 125*F so I would say it is NOT suitable.

Durock Cement board IS specifically listed for the application however.

Gooserider


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## pyrazole

I'm also working on hearth rebuild issues....did some research and found a ceramic product on McMaster (it's all java, I don't know how to link it).  Take a look and feedback.

Extreme-Temperature Sheeting

    * Temperature Range: -425° to +2300° F
    * Heat Flow Rate (K-factor):  1/16" and  1/8" Thick.,  0.71 Btu/hr. x in./sq. ft. @ 800° F;   1/4" Thick., 0.57 Btu/hr. x in./sq. ft. @ 800° F
    * Density: 6-9 lbs./cu. ft.
    * Color: White 

        This alumina silica ceramic fiber is ideal for both high- and low-temperature applications. If exposed to oil or water, it isn't permanently affected—its thermal and physical properties restore after drying.
Thick.     6" x 100 ft.     12" x 50 ft.     24" x 25 ft.     Each
 1/16"     93285K22     93285K24     93285K26      $65.13 
 1/8"     93285K42      93285K44     93285K46       113.63 
 1/4"     93285K62      93285K64     93285K66      235.39 
        6" x 20 ft.        12" x 10 ft.  24" x 5 ft.      
 1/8"     93285K12     93285K15    93285K18  $28.52 

Certainly pricier than durock, but the size is enough to do a couplefew layers on a typical size hearth....low K's, for sure.  Are the K's listed for 1"? or for the respective thickness? I don't know  If they are, you're getting R of 1.40 for the 1/16 and 1/8 (@800F!) and R=1.75 for the 1/4".  If it's per inch ratings, they're not good at all (R's of .08 on the 1/16, .16 on the 1/8, .43 on the 1/4) .  The problems I see:  they don't say specifically that it's fireproof, but alumina-silica should be unless they use an organic binder or something...2300F is a lot to ask for anything organic so I doubt it.  It's also hard to say how compressible it is...spacers or high hats would fix that, though.


----------



## GVA

pyrazole said:
			
		

> I'm also working on hearth rebuild issues....did some research and found a ceramic product on McMaster (it's all java, I don't know how to link it).  Take a look and feedback.
> 
> Extreme-Temperature Sheeting
> 
> * Temperature Range: -425° to +2300° F
> * Heat Flow Rate (K-factor):  1/16" and  1/8" Thick.,  0.71 Btu/hr. x in./sq. ft. @ 800° F;   1/4" Thick., 0.57 Btu/hr. x in./sq. ft. @ 800° F
> * Density: 6-9 lbs./cu. ft.
> * Color: White
> 
> This alumina silica ceramic fiber is ideal for both high- and low-temperature applications. If exposed to oil or water, it isn't permanently affected—its thermal and physical properties restore after drying.
> Thick.     6" x 100 ft.     12" x 50 ft.     24" x 25 ft.     Each
> 1/16"     93285K22     93285K24     93285K26      $65.13
> 1/8"     93285K42      93285K44     93285K46       113.63
> 1/4"     93285K62      93285K64     93285K66      235.39
> 6" x 20 ft.        12" x 10 ft.  24" x 5 ft.
> 1/8"     93285K12     93285K15    93285K18  $28.52
> 
> Certainly pricier than durock, but the size is enough to do a couplefew layers on a typical size hearth....low K's, for sure.  Are the K's listed for 1"? or for the respective thickness? I don't know  If they are, you're getting R of 1.40 for the 1/16 and 1/8 (@800F!) and R=1.75 for the 1/4".  If it's per inch ratings, they're not good at all (R's of .08 on the 1/16, .16 on the 1/8, .43 on the 1/4) .  The problems I see:  they don't say specifically that it's fireproof, but alumina-silica should be unless they use an organic binder or something...2300F is a lot to ask for anything organic so I doubt it.  It's also hard to say how compressible it is...spacers or high hats would fix that, though.


Just throw up the link...... http://www.mcmaster.com/
and the page
page..3382 (For info)


----------



## mtalea

I use alot of cement board in my trade perhaps way to much....durock is considered the best in the construction trade but remember all of them have styrofoam lil balls in it


----------



## Gooserider

Well if Durock uses styrofoam in it's makeup, it's in bits to small to see, and it isn't mentioned in ANY of the documentation that I've seen...  The only product of the cement boards that I've looked at which CLEARLY uses styrofoam is Permabase - you can see the beads, they are mentioned in the product documentation, and is the reason why I was told by the Permabase tech support people that it is "Not non-combustible" (love those double negatives :smirk: )

Hardibacker contains wood cellulose fibers - their tech support says that it is NOT reccomended as floor protection, but is fine for NFPA protection walls.

Wonderboard uses fiberglass and seems to have a max reccomended temperature exposure - again, not good for floors, OK for walls

Durock specifically says "NON COMBUSTIBLE, WILL NOT BURN" and has documentation that specifically reccomends it's use in floor protectors as well as NFPA protection walls

As to the McMaster Carr stuff, I haven't looked it up yet, but from the description and GVA's comments, it might be OK or not depending on how compressible it is.  The R-value is pretty good - Micore is R-1.1 per half inch, this stuff would be R-0.86 per half inch, which isn't as good, but better than Cement board, and enough to get into the R-1.1 range w/ a layer of Durock, enough for many stoves.  The question is whether or not it would offer the structural rigidity and non-compressibility that you'd need for building a floor?

Gooserider


----------



## MrKenmore

What exactly is the construction going to be for this application?  cement board on the studs with stone/masonry/ceramic on it?  I'm just curious what the finished product will be.


----------



## ChillyNoMore

Having read through this entire discussion, I'm still a bit confused... Since the HardiBacker is non-combustable, can it be used for ember protection all by itself? (I need something temporary to put down over the existing wood floor in order to get my stove installed before I freeze my a$$ off!) Down the road, I will do a full-blown tile hearth for my Scan 61 (which only requires ember and not thermal protection).


----------



## Scrat

I too am a bit confused. Which one would be the best to use for a corner wall install with porcelin tile on it. I would leave a space between the sheetrock and the wallboard the the tile would go on. THanks.


----------



## begreen

Hardibacker has cellulose fillers and is not the ideal product to use for a hearth, especially if it is the final and only surface. Pure cement board like Durock or Wonderboard are preferred. However, be careful to get the original product. Both companies now also make a next generation version of their cement boards that have styrofoam filler in them.

Either Durock or Wonderboard 1/2" cement board product is good for a wall shield. USG has instructions on their website for making a wall shield using Durock.


----------



## G-rott

If ember protection is all that is needed, I would use hardi backer,  I might mix up a little thinset and skim coat the top surface just for looks and to enclose any fiberglass or cellulose fibers.  Also if you are not going to remove all the hardwood under the "protector" I would get one of the nonskid rug pads made of the thin foam and place it under the hardi to protect the flooring you are keeping.

Garett


----------



## djblech

The problem with this stuff I found out recently is that without an air space behind it will still transfer to much heat to the materials behind or beneath. I used hat channel on the walls to fir out the cement board and achieve the air space/flow. Most of the codes are written as suggestions thereby leaving the design/builder on the hook if anything happens. I was going to install a class A chimney about a month ago, I called my liability insurance  and found out they would not cover me if anything happened. Needless to say, I passed on the job, even though I have installled chimney's for myself with no problems. 
Doug


----------



## carinya

As a totally unrelated aside.......

A cheap house construction material in the middle of last century, "fibro" panels were used extensively for exterior & interior wall construction, and roofs, in Australia.  As kids we loved to throw pieces of fibro in a fire.....and enjoy the exploding results.  :lol: 

Little did we know about asbestos  :-S 

As for cutting...it's a piece of cake with the right equipment

eg     http://www.malcoproducts.com/products/shears/index.asp


----------



## Blazin

Gooserider said:
			
		

> dmt5000 said:
> 
> 
> 
> 
> Ddes anyone know anything about USG "Fiber Rock" underlayment, i.e., is it suitable for a tile backer under a wood stove? Thanks,
> 
> 
> 
> 
> Just looked it up - their Submittal sheet #F102 for it on the
> FibeRock web page says it shouldn't be exposed to sustained temps over 125*F so I would say it is NOT suitable.
> 
> Durock Cement board IS specifically listed for the application however.
> 
> Gooserider
Click to expand...


Has anyone checked into the Fiberock Backerboard?  It's listed on USG's site as being fire rated.

http://www.usg.com/fiberock-aqua-tough-tile-backerboard-panels.html

I'm asking because the local flooring retailer stocks it.


----------



## Blazin

I e-mailed USG about the FibeRock backerboard and this is the reply I recieved:

*Our Fiberock Backerboard has an R value of .3 Hr FtÂ² Â°F/Btu, our Durock Cement board has one of .26

Regards,

Chris Curtiss*


----------



## begreen

Last I checked, fiberrock is not to be used for hearth construction or wallshields. It has 15% cellulose content. 

From the USG data sheet for this product:

*5. Panels should not be exposed to sustained temperatures above 125 Â°F (51.6 Â°C).*

http://www.usg.com/fiberock-aqua-tough-tile-backerboard-panels.html#tab-literatureAndVideos

The hearth and the walls can see higher sustained temps than 125F. Don't use this.


----------



## Renovation

BeGreen said:
			
		

> Last I checked, fiberrock is not to be used for hearth construction or wallshields. It has 15% cellulose content.
> 
> From the USG data sheet for this product:
> 
> *5. Panels should not be exposed to sustained temperatures above 125 Â°F (51.6 Â°C).*
> 
> http://www.usg.com/fiberock-aqua-tough-tile-backerboard-panels.html#tab-literatureAndVideos
> 
> The hearth and the walls can see higher sustained temps than 125F. Don't use this.



I believe you, and this is confusing.  Right on the page it says "fire-rated".  That seems misleading.


----------



## Blazin

Well, this is definitely confusing.  I found where the data sheet says the shouldn't be exposed to temps over 125F.

Just above that is this: Fire Resistant These panels offer superior fire resistance and demonstrate exceptional surface burning characteristics.

With such a low temp listed in the data sheet, I hope no one tries to use them in Arizona...


----------



## Renovation

Blazin said:
			
		

> Well, this is definitely confusing.  I found where the data sheet says the shouldn't be exposed to temps over 125F.
> 
> Just above that is this: Fire Resistant These panels offer superior fire resistance and demonstrate exceptional surface burning characteristics.
> 
> With such a low temp listed in the data sheet, I hope no one tries to use them in Arizona...



Yep, that sure makes things easy for the consumer, who's trying to be safe and researching the product.   :roll:


----------



## LLigetfa

RenovationGeorge said:
			
		

> I believe you, and this is confusing.  Right on the page it says "fire-rated".  That seems misleading.


5/8" drywall is "fire rated" so you just need to understand the context of what its use is.

As for Durock and their NexGen product, does anyone have details on its makeup WRT high temp exposure compared to the old product?  From what I gather, it looks like they phased out the old product.


----------



## RNLA

Does it change anything if you are putting all the stone or tile or whatever on the board. Is it only rated as the bare board???? Someone PM me we are about to do an install and was going to do hardibacker....


----------



## begreen

There's a difference between a fire resistant barrier intended to resist the spread of fire and a totally non-combustible product that also is an excellent substrate for stone or tile. Durock can't burn, neither can unpapered drywall, but the drywall would make a poor substrate because it would soak up the moisture from thinset or mortar. Would Hardibacker work on a low heat hearth as substrate? Probably, especially if the stove bottom is well shielded. But if the hearth is built in as part of the house infrastructure, who is to say what stove will be on the hearth 10 or 20 yrs from now and what the hearth requirement will be. IMO, this is a good place to overkill a bit. 

That said, I've spent hours trying to get some definitive answers on the subject. USG is clear about Fiberrock, Hardie is not so explicitly clear for a similar product. There doesn't seem to be a consistent answer here. On one building inspector forum I even found a couple inspectors suggesting Hardibacker and then getting corrected.


----------



## Blazin

Well, I'm convinced that I'll have to drive to Lowes or HD and pick up some Durock.  The problem with small towns and big states is readily apparent when either of the big DIY retailers is over 200 miles away.


----------



## OrpingtonManor

Really glad to see this thread.  After reading it, I went back to the pics I had taken when I renovated the sunporch where I will be installing my Morso 1410.  The floor is slate, but the underlayment is USG Fiberrock.  I could have sworn we used Hardiebacker, but not so. Good thing I still have a bunch of slate. I will now be building a hearth.


----------



## LLigetfa

Ja, but when you get there, will they have the classic Durock or NexGen?  I think the jury is still out on NexGen.


----------



## Blazin

LLigetfa said:
			
		

> Ja, but when you get there, will they have the classic Durock or NexGen?  I think the jury is still out on NexGen.



I'll be sure they have what I need before I go.  Thanks for mentioning the nexgen, I wasn't aware there was such a thing.


----------



## begreen

Blazin said:
			
		

> Well, I'm convinced that I'll have to drive to Lowes or HD and pick up some Durock.  The problem with small towns and big states is readily apparent when either of the big DIY retailers is over 200 miles away.



Yes, we have the same issue. Call local lumber yards. With lower volume sales they may still have a stash of the original Durock or Wonderboard.


----------



## OrpingtonManor

I used to get my Hardiebacker at HD, and didn't think anything of it when they switched their stock to Fiberock.  I wish I'd known then what I know now.


----------



## Intheswamp

OrpingtonManor said:
			
		

> Really glad to see this thread.  After reading it, I went back to the pics I had taken when I renovated the sunporch where I will be installing my Morso 1410.  The floor is slate, but the underlayment is USG Fiberrock.  I could have sworn we used Hardiebacker, but not so. Good thing I still have a bunch of slate. I will now be building a hearth.


A little off topic but...how are those buff orps doing? 

Ed


----------



## OrpingtonManor

Intheswamp said:
			
		

> OrpingtonManor said:
> 
> 
> 
> 
> Really glad to see this thread.  After reading it, I went back to the pics I had taken when I renovated the sunporch where I will be installing my Morso 1410.  The floor is slate, but the underlayment is USG Fiberrock.  I could have sworn we used Hardiebacker, but not so. Good thing I still have a bunch of slate. I will now be building a hearth.
> 
> 
> 
> A little off topic but...how are those buff orps doing?
> 
> Ed
Click to expand...

The Buff Orps are mostly freeloading at the moment.  Only one of them is laying.  The rest are either molting, taking a winter vacation, or on bug/weed patrol.   Good thing they're entertaining.


----------



## The Dude

I have two related questions for my own install. I am about to install my vented clearance reduction board on the wall behind and beside my wood stove, and I just dug up this thread by Googling "Is hardibacker combustible?"  (It's funny how all important things along the way point me to this forum).  

My first question is regarding strength of hardibacker and durock nexgen, in which I heavily favor hardi. I will be facing the cement board with thin stone. I worry that the added weight combined with it only being supported from behind every 16", that someone could lean on it or bump something into it and the board could crack.  I bought both types of board, and the durock breaks MUCH easier, with only slight bending.  It is still held together by the outer mesh, but I can't risk it breaking and having a wobbly, crumbling spot in my wall.  Hardibacker seems to hold up much better.  I thought about the theoretical risk with the cellulose fibers, but my stove manual (Harman TL-300) specifies non-combustible and this is listed as so.  And I'll be creating a thermal airspace behind it.  Does anyone advise against me using hardibacker?  

My other question regarding heat transfer to the studs.  I cut 3" wide strips of hardibacker to use for spacers between my painted drywall and the cement board shield.  In order to support the weight of the cement board and stone, I figure my only option is to screw the board and spacers into the studs.  What I can't figure out is if this will defeat the purpose of the vented spacing by transferring heat right through the spacers and into the studs.  If I understand correctly, the studs are the most critical combustible material that I'm trying to protect in the first place. Any advice? Thanks!


----------



## tfdchief

Edit


----------



## mhrischuk

My observations of Next Gen Durock

https://www.hearth.com/econtent/index.php/forums/viewthread/76389/P66/


----------



## mhrischuk

On edit. I called USG Engineering. They said do not use Durock Next Gen for high heat applications over 200 deg. It is not tested.


----------



## The Dude

Thanks for the info!  I actually tried using Durock but one board crumbled, so I tested the other one to see if it could take pressure when being suspended off the wall with spacers, and just by pressing a little on a space in between studs the board cracked.  That would SUCK if it happened after I mortared my natural stone veneer onto it, built the mantle, and put the stove back in place.  So I went with Hardibacker even though it has the cellulose fibers.  Aside from that theoretical concern, it seems superior in workability and strength to me.


----------



## mhrischuk

I'm not sure if this is what you are talking about. It does crack normally when handled but when properly installed and supported, once it's covered in tile it should be a non-issue. After all, it is a sheet of cement. But after what you described, I don't blame you. I might have done the same. My application is laying flat on the floor.



> 12. Panel Micro-Cracking Durock cement board is formulated to develop fine micro-cracking (also called as multiple-cracking) in the panel. The micro-cracking process helps to evenly relieve the stored strain energy in the product due to handling and
> installation, external loads, and/or panel restrained movement. The presence of micro-cracks in the panel should
> not be considered a product defect.


----------



## The Dude

I think that is the crumbling I was speaking of.  But when a whole board cracked all the way through and only held together by the fiberglass in the faces, that was as broke as a I am (really broke!).  The thing is, I was using it in an unusual way, suspended an inch out from the wall, and pretty much unsupported according to it's intended purpose (see picture).  I was so worried that if someone ever leaned against it in between the rows of spacers, the whole thing would crack.  I think if it is used solidly against something, this would not be an issue. And considering how you showed me that those little white balls on the interior are not the flammable styrofoam that I thought they were, I'd say it's the most cement-based looking board out there.  I had two issues for my project, the combustible one which you proved wrong, and the fragility, which probably isn't an issue in most people's projects.  So it looks like we are in two different boats here!


----------



## mhrischuk

Are those spacers designed for this application?


----------



## The Dude

Yes, ceramic spacers.  I initially planned on using durock strips for spacers (see pic), but got too hung up on the idea of air circulation being limited to within the channels, while solid strips were placed directly over the studs, allowing heat transfer to the main material that the shield tries to keep heat away from.


----------



## The Dude

Completed wall with heat shield and stove installed.  Thin creek stone to be installed over cement board soon.


----------



## mhrischuk

Looks good. Another option would have been just squares of board as spacers.


----------



## The Dude

Excellent idea!


----------



## begreen

Nice job, it looks good. This looks like it was done exactly as USG suggested in their old wall shield pamphlet. The furring strips are easier to cut and install and they provide a firm flat backing for the wall shield.


----------



## mhrischuk

I just got off the phone with engineering technical support for USG.

He sad NO,       * Durock Next Gen is not qualified and tested for over 200 deg.*


----------



## begreen

True, they haven't tested it in the US, but from the documentation it appears that their Canadian arm did and endorses it for this application. If you read all the posts on this topic you will see that it's now a judgement call. After determining that unlike Permabase, the NextGen product uses perlite for the lightening filler, I have no problems recommending Durock NextGen.

I would recommend that all write the HPBA and USG requesting testing of these NextGen products so that this issue can officially be put to rest.


----------



## mhrischuk

BeGreen said:
			
		

> True, they haven't tested it in the US, but from the documentation it appears that their Canadian arm did and endorses it for this application. If you read all the posts on this topic you will see that it's now a judgement call. After determining that unlike Permabase, the NextGen product uses perlite for the lightening filler, I have no problems recommending Durock NextGen.
> 
> I would recommend that all write the HPBA and USG requesting testing of these NextGen products so that this issue can officially be put to rest.



I agree.

The engineer basically said they no longer recommend it for stove applications but he also said it hasn't been tested. 

Looking at it closely it looks almost like solid cement I don't see any other ingredients like you do with Permabase.

He simply said there was a major formula change and it was not tested for use in fireplaces. What gets me is all of those places out on the net that mention it. His response was yes but we do not state it in our documents.


----------



## begreen

True, they haven't tested it in the US, but from the documentation it appears that their Canadian arm did and endorses it for this application. If you read all the posts on this topic you will see that it's now a judgement call. After determining that unlike Permabase, the NextGen product uses perlite for the lightening filler, I have no problems recommending Durock NextGen.

The supply of the original Durock and Wonderboard ran out this year. Now in the US there is no tested product. Pragmatically, the NextGen product is the only alternative we know of. It has been approved in Canada, which generally has stiffer hearth standards. I would recommend that all write the HPBA, Custom Building Products and USG requesting testing of these NextGen products so that this issue can officially be put to rest.


----------



## mhrischuk

I'm using it. I just talked to another guy from there. Basically what they are saying is it won't do a good job of protecting the surface it's covering but it will not burn.


----------



## begreen

I think what they are saying is that they have not officially tested if for this purpose. In Canada, apparently they have. Take a moment to write a letter or email to them and the HPBA. It would be great to have this product certified for hearth use in the US once again.


----------



## TK-421

Does anyone have any updates on the durarock?

I'm getting ready to build a heart pad for most likely an Englander 30nc.  I had planned on going with three layers of 1/2" durarock to get an R-value of .75' then ceramic tiled above all screwed to each other and screwed to 3/4" plywood to protect my hardwood floors.

Reading this article I'm now hesitant to use it as I'm worried about whether or not an insurance provider would take issue with it should a fire occur.

Thought?  Alternatives?  I guess worst case with the cheap price of the 30 I could just buy an approved hearth pad but I'm a DIYer and hate to waste money on something I could do myself.


----------



## mhrischuk

Ignore pretty much everything I said previously in this thread. I'm using it. I don't think there is an issue with it at all. The feeling most of us who called USG and spoke to the engineers got was that since they reformulated to the NextGen product, they simply didn't take the testing to the next level for higher temperature shielding. I think they simply aren't interested in the hearth market and it's possible liability implications in the US. Just because they don't have a sentence in their data sheet that recommends it for hearth applications does not mean it won't perform. Their Canadian leg of the company does in fact list it as a hearth substrate solution. I asked the engineer at USG if there is a different board formulation for Canada and if there is a different manufacturing plant for Canada. The answer was all of the board is the same and it's all made at the same plant for North America.


----------



## TK-421

I just pulled this off their site.


The board is non-combustible and can be used in a variety of fire-rated designs. Its low thermaland hygrometric expansion help prevent finish cracking.

They also have links, upper right, that state fire, and class A.  I ant access them with my iPad so I'm not sure what they say.


Even using them you still need 4 sheets at .25 each then your tile on top.  I checked tile and got .01 R. 

That's a lot of weight to add.  Seems a prefab pad might be better even though the cost is more.


----------



## pen

What the heck is inside the pre-fab pads?

pen


----------



## TK-421

pen said:
			
		

> What the heck is inside the pre-fab pads?
> 
> pen



My very question.  Space shuttle tiles. . They are so thin.   Maybe 1-2" at best.


----------



## Fred61

mhrischuk said:
			
		

> Looks good. Another option would have been just squares of board as spacers.



I've used ceramic cabinet drawer pulls as spacers.


----------



## ScotO

Hey fellas I was at Home Depot to buy some non combustible backerboard, they had both Hardiebacker and Durock.....I had bought Durock before but as I was loading this Durock on the cart recently, I noticed it had little styrofoam balls encapsulated in it.....that CANNOT be good for fire rated walls.....I imagine they did that to cut down on the weight a little, but I would not trust using that as a non combustible backer.....I held a map gas torch against some 1/2" Hardiebacker for several minutes (till it was glowing orange on one side) and you could still touch the other side with your bare hand.....I would trust the Hardiebacker board over all else esp. in a situation like mine where you are going to install tile or stone veneer.......just my two cents.....


----------



## Delta-T

Flamegrower said:
			
		

> Hey fellas I was at Home Depot to buy some non combustible backerboard, they had both Hardiebacker and Durock.....I had bought Durock before but as I was loading this Durock on the cart recently, I noticed it had little styrofoam balls encapsulated in it.....that CANNOT be good for fire rated walls.....I imagine they did that to cut down on the weight a little, but I would not trust using that as a non combustible backer.....I held a map gas torch against some 1/2" Hardiebacker for several minutes (till it was glowing orange on one side) and you could still touch the other side with your bare hand.....I would trust the Hardiebacker board over all else esp. in a situation like mine where you are going to install tile or stone veneer.......just my two cents.....



those styrofoam balls...could they be perlite or vermeculite? looks and tastes like styrofoam (ok, i dunno what it tastes like, but they look like styrofoam)


----------



## ScotO

Delta-T said:
			
		

> Flamegrower said:
> 
> 
> 
> 
> Hey fellas I was at Home Depot to buy some non combustible backerboard, they had both Hardiebacker and Durock.....I had bought Durock before but as I was loading this Durock on the cart recently, I noticed it had little styrofoam balls encapsulated in it.....that CANNOT be good for fire rated walls.....I imagine they did that to cut down on the weight a little, but I would not trust using that as a non combustible backer.....I held a map gas torch against some 1/2" Hardiebacker for several minutes (till it was glowing orange on one side) and you could still touch the other side with your bare hand.....I would trust the Hardiebacker board over all else esp. in a situation like mine where you are going to install tile or stone veneer.......just my two cents.....
> 
> 
> 
> 
> those styrofoam balls...could they be perlite or vermeculite? looks and tastes like styrofoam (ok, i dunno what it tastes like, but they look like styrofoam)
Click to expand...


the board I was looking at (if my memory serves me rigth) looked like pink or light purple balls....not sure I ever say light purple vermiculite.....lol.....


----------



## TK-421

I highly doubt it is styrofoam especially since this has been approved by our northern friends.

Put a torch to them and see if they shrivel.  Highly doubtful.  Be careful whenever using a torch on things that could gas.  Styrofoam gives off major toxins.


----------



## ScotO

TK-421 said:
			
		

> I highly doubt it is styrofoam especially since this has been approved by our northern friends.
> 
> Put a torch to them and see if they shrivel.  Highly doubtful.  Be careful whenever using a torch on things that could gas.  Styrofoam gives off major toxins.



I went with hardiebacker just to be safe.......It's listed as non-combustible and I also redneck tested it with a torch and I trust it, plus it seems to hold the cement pretty good......also easier to cut and run screws into ......


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## Fred61

Flamegrower said:
			
		

> Hey fellas I was at Home Depot to buy some non combustible backerboard, they had both Hardiebacker and Durock.....I had bought Durock before but as I was loading this Durock on the cart recently, I noticed it had little styrofoam balls encapsulated in it.....that CANNOT be good for fire rated walls.....I imagine they did that to cut down on the weight a little, but I would not trust using that as a non combustible backer.....I held a map gas torch against some 1/2" Hardiebacker for several minutes (till it was glowing orange on one side) and you could still touch the other side with your bare hand.....I would trust the Hardiebacker board over all else esp. in a situation like mine where you are going to install tile or stone veneer.......just my two cents.....



It should be pearlite. I don't think styrofoam balls would survive the mixing process. There must have been some serious stresses on the board in order to have the balls turn purple. IMHO.


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## begreen

It is not styrofoam, it's perlite, as already discussed in this thread. 

Durock and Wonderboard NexGen products are also listed as non-combustible.


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## jimbom

I do the MAPP gas torch test on things myself.  Didn't really consider out gas issues.  Thanks for the tip.  It is nice to read so and so material is classified such and such.  However, when you torture test it yourself, you know what is what.


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## begreen

pen said:
			
		

> What the heck is inside the pre-fab pads?
> 
> pen



I'm guessing MicoreÂ® SB mineral fiber board for the insulation and not sure about the backerboard. Give the folks at Yoder a call.


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## ScotO

JimboM said:
			
		

> I do the MAPP gas torch test on things myself.  Didn't really consider out gas issues.  Thanks for the tip.  It is nice to read so and so material is classified such and such.  However, when you torture test it yourself, you know what is what.



AMEN Jimbo.....I ALWAYS do the redneck stress test on items, especially if I am using them with consequences.......my friends don't call me Scotty Overkill for nothin....lol.....


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## ScotO

Fred61 said:
			
		

> Flamegrower said:
> 
> 
> 
> 
> Hey fellas I was at Home Depot to buy some non combustible backerboard, they had both Hardiebacker and Durock.....I had bought Durock before but as I was loading this Durock on the cart recently, I noticed it had little styrofoam balls encapsulated in it.....that CANNOT be good for fire rated walls.....I imagine they did that to cut down on the weight a little, but I would not trust using that as a non combustible backer.....I held a map gas torch against some 1/2" Hardiebacker for several minutes (till it was glowing orange on one side) and you could still touch the other side with your bare hand.....I would trust the Hardiebacker board over all else esp. in a situation like mine where you are going to install tile or stone veneer.......just my two cents.....
> 
> 
> 
> 
> It should be pearlite. I don't think styrofoam balls would survive the mixing process. There must have been some serious stresses on the board in order to have the balls turn purple. IMHO.
Click to expand...


you got a point there Fred....I've had blue balls before but never purple......lol.....


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## ScotO

BeGreen said:
			
		

> It is not styrofoam, it's perlite, as already discussed in this thread.
> 
> Durock and Wonderboard NexGen products are also listed as non-combustible.



Thanks BeGreen......I like using the Durock, esp. for any veneer job I am doing, but wasn't sure about that stuff....the stuff I bought two years ago did not have perlite in it.....did they recently start putting it in the board?......


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## pen

Not saying that I recommend this (I'll say it again, DO NOT DO IT), but my buddy who's an oaf has a 30 and destroyed his baffle boards.  Rather than cough up the 120 bux or so for 2 new ones, he went out and bought a sheet of next gen durorock.  He cuts them and uses them in place of the factory baffle.  He puts a new set in at the beginning of winter, and changes it out once during the winter.  2 sets get his stove through an entire season.  He burns about 5 cord of wood through his 30.  The wood stove is his only heat.

If it can survive for months IN a stove, I have no concerns placing it under one.

pen


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## ScotO

pen said:
			
		

> Not saying that I recommend this (I'll say it again, DO NOT DO IT), but my buddy who's an oaf has a 30 and destroyed his baffle boards.  Rather than cough up the 120 bux or so for 2 new ones, he went out and bought a sheet of next gen durorock.  He cuts them and uses them in place of the factory baffle.  He puts a new set in at the beginning of winter, and changes it out once during the winter.  2 sets get his stove through an entire season.  He burns about 5 cord of wood through his 30.  The wood stove is his only heat.
> 
> If it can survive for months IN a stove, I have no concerns placing it under one.
> 
> pen



Pen I have read on this forum different guys who do that......and I will +1 on what you said...DON'T DO IT.......if for nothing else, say those boards fail in the middle of the night and next thing you know your stove top is exposed to full heat from the fire, then warps all to hell.....but like you said, if it can withstand heat like that, surely it is good enough for the underlayment or for the surround....


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## mhrischuk

Durock has no combustible ingredients.

Portland Cement <50 
Fly Ash <50 
Expanded Clay Aggregate <30 
Or Expanded Shale Blend of Proprietary Mineral Based Ingredients <20 
Fiber Glass Scrim <5 
Crystalline Silica <5

http://www.usg.com/rc/msds/panels/durock/durock-cement-board-msds-en-14090001.pdf

http://www.usg.com/rc/data-submittal-sheets/panels/durock/durock-cement-board-submittal-CB399.pdf


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## begreen

Flamegrower said:
			
		

> BeGreen said:
> 
> 
> 
> 
> It is not styrofoam, it's perlite, as already discussed in this thread.
> 
> Durock and Wonderboard NexGen products are also listed as non-combustible.
> 
> 
> 
> 
> Thanks BeGreen......I like using the Durock, esp. for any veneer job I am doing, but wasn't sure about that stuff....the stuff I bought two years ago did not have perlite in it.....did they recently start putting it in the board?......
Click to expand...


The warehouses started emptying out of the old pure cement board products last year. To my knowledge they are no longer available unless found in the dusty recesses of a quiet lumber yard. Hardibacker may be fine, but I'm reticent to recommend it because it has cellulose mixed in. The competing product made by USG is Fiberock which specifically says to not use the product in high temp locations. 

 As you have noted, this discussion is as old as Elk from days before this forum started. It comes up annually and has been confused by the NextGen products. We do the best we can to investigate and respond based on the current market options. There is only one agenda here and that is to help others to make their installations safe and functional. If the recommendation seems narrow, it is because the answer speaks not just to a single installation, but to the hundreds that will read the thread later on.


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## Jags

BeGreen said:
			
		

> As you have noted, this discussion is as old as Elk from days before this forum started. It comes up annually and has been confused by the NextGen products. We do the best we can to investigate and respond based on the current market options. There is only one agenda here and that is to help others to make their installations safe and functional. If the recommendation seems narrow, it is because the answer speaks not just to a single installation, but to the hundreds that will read the thread later on.



Well spoken BG.  I really comes down to the fact that the Nexgen Durock has NOT been tested in the USA for hearth applications. That doesn't mean it is not the proper product, it just has not been tested for it in the US (it HAS been tested in Canada, an meets their requirements)


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## mhrischuk

Jags said:
			
		

> BeGreen said:
> 
> 
> 
> 
> As you have noted, this discussion is as old as Elk from days before this forum started. It comes up annually and has been confused by the NextGen products. We do the best we can to investigate and respond based on the current market options. There is only one agenda here and that is to help others to make their installations safe and functional. If the recommendation seems narrow, it is because the answer speaks not just to a single installation, but to the hundreds that will read the thread later on.
> 
> 
> 
> 
> Well spoken BG.  I really comes down to the fact that the Nexgen Durock has NOT been tested in the USA for hearth applications. That doesn't mean it is not the proper product, it just has not been tested for it in the US (it HAS been tested in Canada, an meets their requirements)
Click to expand...


And it is the exact same product, manufactured in the US in the same factory and shipped to Canada. (I was told by USG)


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## PROOT

Does anyone have new info on Durock nex gen vs permabase


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## begreen

They seem to be a very similar product with similar ingredients. National Gypsum lists the lightening ingredient in Permabase as pozzolan which is volcanic tuff.

http://www.nationalgypsum.com/products/Product.aspx?ProductID=2393


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## timusp40

_
From the Woodstock Web Site,
Technical Note: Conductivity
Cement backer board is an ideal material for a hearth pad because of
its low “k”, or conductivity value. Conductivity is the ability to conduct
heat. The lower the “K” factor, the less heat is conducted through
the material. For example, Durock has a k-value of 1.92 per inch, as
compared to the k-value of common brick, which is 5.00 per inch, or
marble, which has a k-value of 15.00 to 20.00 per inch.

So I put 1" of next gen under my tile. Passed inspection here in Michigan no problem.
Take Care,
Tim_


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