# Hearth Pad Cement Board - I'm Confused



## leeave96 (Sep 25, 2010)

Searching and reading through posts, I am trying to figure-out what cement/insulation board to use on my hearth pad.

The manual for my Woodstock Keystone says "...a 1/2 inch layer of an approved non-combustable insulation board such as Durock cement boad or Wonderboard backerboard..."

However, searching and reading through some of the posts, some feel the Next Gen Durock is not for hearth applications and there are negative views on Wonderboard.

I cannot find the original Durock in my neck of the woods, but the Next Gen Durock is available.  Further, on the USG website, it states the Next Gen Durock is "non-combustable" and to me that squares with my stove manual requirements for a hearth pad.

Can I use Next Gen Durock with my Woodstock stove for a hearth pad?

If not - then what?

Thanks!
Bill


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## nate379 (Sep 25, 2010)

Yes.  Whoever is saying you can't is on drugs.

Hell just for S&G I took a piece I cut off my pad and tried to light it with my torch.... torch is what, 5500-6000*... somewhere around that.


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## begreen (Sep 25, 2010)

If you can get Wonderboard cement board or the original Durock cement board, that would be best. But I suspect that sooner or later we will have to start using USG next gen in spite of it not being officially tested. There is only so much of the original cement board around.


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## Dakotas Dad (Sep 25, 2010)

NATE379 said:
			
		

> Yes.  Whoever is saying you can't is on drugs.
> 
> Hell just for S&G I took a piece I cut off my pad and tried to light it with my torch.... torch is what, 5500-6000*... somewhere around that.



Actually, people on this very board have talked to the engineers at the factory and have been told, by them that NextGen is not hearth approved.

*OP,* what troubles did you read about Wonderboard? Other than it's heavy as all get out, I found it very easy to work with.


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## pen (Sep 25, 2010)

I do NOT recommend using unapproved materials for any job.  However, I just thought I'd share a small bit of experience I have had w/ hardibacker in hot places.

Take a look at this pic....







When fixing the inadequate thimble for my stove, I needed something to place above the crock to hold the bricks as I continued higher.  All I had that would fit the bill was hardibacker.  I used it figuring if I ever saw any wear or sign of overheating on it that I would simply knock it out since it's unnecessary now that the mortar has dried.  After 2 seasons of burning where it lives literally right on top of the stove pipe it looks as good as the day it was installed.

Considering what temps it sees here, I just can't believe there ever would be a problem under a stove using the stuff.  But, I guess the regulations say otherwise.

pen


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## nate379 (Sep 26, 2010)

I would not doubt they say "no" just to cover their behind and nothing more than that.

If the stuff doesn't light up with a 6000* torch, how can that not be suitable to be used for a hearth?  In most installs it's just a backer for tile (which wonderboard is made for).  Tile isn't going to catch fire anyhow, so it's really just an extra in case if.

The pad is just there to catch any embers or in the case of a fireplace maybe a log that rolls out (have had it happen before), hardly anything close to 6000*!

About the only thing I could think of that would be "approved" would be asbestos sheets and I don't think you can even still buy it anymore.


When the guys came to install my stove they said my pad was very overbuilt even.  2 layers of 3/4" plywood, a layer of 1/2" cement board, then tiles set in about 3/8" of mortar.




			
				Dakotas Dad said:
			
		

> NATE379 said:
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## jtp10181 (Sep 26, 2010)

NATE379 said:
			
		

> When the guys came to install my stove they said my pad was very overbuilt even.  2 layers of 3/4" plywood, a layer of 1/2" cement board, then tiles set in about 3/8" of mortar.



For some stoves a single 1/2" sheet of durock does meet the required R (or k) value for the stove.

Durock may be non-combustible but it is not that great at resisting heat trasnfer. The problem would arrise if a burning log fell out and sat on the tile for a little bit. In thoery enough heat could transfer thru to start the plywood under the durock on fire.


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## Dakotas Dad (Sep 26, 2010)

NATE379 said:
			
		

> I would not doubt they say "no" just to cover their behind and nothing more than that.
> 
> If the stuff doesn't light up with a 6000* torch, how can that not be suitable to be used for a hearth?  In most installs it's just a backer for tile (which wonderboard is made for).  Tile isn't going to catch fire anyhow, so it's really just an extra in case if.
> 
> ...



You may find that on this board, the members are both trying to do things right, and give sound advice as to what to use and how to use it. 

It's not approved. period. Other materials are or were.

You can hold a torch to it for a week, and it may not even smolder, but IF YOUR HOUSE BURNS DOWN, the insurance company is going to look at every component used, and trust me, you don't want them to find that you used non approved materials. 

Another thing is, while the guys who told you _your_ hearth was overbuilt may be correct, it's just not so for every stove. Your hearth is radically under built for my stove. Some stoves do in fact only require "ember protection", some, like mine, require way more than that. Since we don't know what stove you are using, we don't know what the requirements you needed to meet are/were.


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## begreen (Sep 26, 2010)

Once the existing supply of true cement board is exhausted, what will hearth's be made of? Sounds like we are going to be seeing a lot of welded steel hearths unless we get some movement here. Time to draft a letter to HPBA and USG requesting UL testing for the NextGen product in a hearth as quickly as possible.


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## jtp10181 (Sep 26, 2010)

You guys going to make me do some research....

The cement board or whatever does not need to be tested for use as a fireplace hearth. It just needs to be a listed non-combustible. The Durock Next Gen webpage says it is non-combustible, now I just need to find the specs and listings and match them up with the Quad Manuals which have the non-combustible testing spec numbers listed in them.
-------------------
And... I have struck gold.

Reference Materials: (copy / paste links if you need to, forum does not like the   spaces)

USG Durock Submittal: http://www.usg.com/rc/data-submittal-sheets/panels/durock/durock-cement-board-submittal-CB399.pdf
Random Quad Manual: http://www.quadrafire.com/~/media/Files/Quadrafire/Installation Manuals/man_5700ST_ACC.ashx
Random Heat & Glo Manual: http://www.heatnglo.com/~/media/Files/Heat n Glo/Installation Manuals/2164_900.ashx

Ok... so I checked the Quad manual first.

Unfortunately they only specify _"Non-combustible Material: Material which will not ignite and burn. Such materials are those consisting entirely of steel, iron, brick, tile, slate, glass or plasters, or any combination thereof."_

So then I check a Heat & Glo manual because I know I saw them list a specific test before and I found this:

_"Materials that are reported as passing ASTM E 136, Standard Test Method for Behavior of Materials in a Vertical Tube Furnace at 750 ºC and UL763 shall be considered non-combustible materials."_

So... then I google searched for Durock ASTM testing and found a submittal sheet

_"The information contained in this document applies to Durock® brand cement board and *Durock cement board Next Gen*."_

_"Non-combustibility Pass/Fail E136 Pass Pass"_

The only thing I want to do still is find reference from the the Durock page to the submittal. I am not sure what exactly that submittal is, it looks official but I want to be sure. What other materials should we check on?


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## begreen (Sep 26, 2010)

IIRC the R value for Durock NextGen is the same as for the old product. R=.52/inch.


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## jtp10181 (Sep 26, 2010)

So.... who started all thus hubbub about the Next Gen Durock not being OK for under hearths? Looks good to me, any objections?

Don't forget, to get a good heat resistance value you still need something like 1/2" Micore 300, or I think 2" (4 sheets) of durock. One sheet of durock does not cut it if your stove requires more than just ember protection.

Oh and I found the link to the submittal through their page:

http://www.usg.com/durock-cement-board.html#tab-literatureAndVideos

Its under the "Data/Submittal Sheets" section.
----

I also found this, which is where people are probably thinking that the original Durock was OK, and NextGen is not

http://literature.usg.com/pdf/CB198.pdf

This shows the original Durock was specifically tested and even had instructions for how to install it as a floor or wall protector. This is designed for back in the day when stoves had 36" clearances required and you needed to reduce them or have it sit in the middle of the room. It also states "DUROCK Cement Board may also be used as a floor protector in place of one layer of 3/8" thick millboard." which until recently the Quad manuals still specified to use 3/8" millboard or equivalent for hearth protection, which no one could even tell me what millboard was. Best speculation was asbestos board which you are not going to find anywhere...

So... present day, stove manufactures are just specifying that you have to use some sort of non-combustible, and they may also specify you need a certain R or k value. Both of which Durock NextGen can provide (if you use enough sheets).

Any questions?


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## roberth42 (Sep 26, 2010)

I have a PDF file from the manufacturer about Next Gen and it's use for hearth pad and wall shield.

I emailed the manufacturer and I have it in writing from them that it is safe for this application. if anyone wants a copy I can PM it. It's a PDF file so I cannot upload it to this forum.


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## jtp10181 (Sep 26, 2010)

roberth42 said:
			
		

> I have a PDF file from the manufacturer about Next Gen and it's use for hearth pad and wall shield.
> 
> I emailed the manufacturer and I have it in writing from them that it is safe for this application. if anyone wants a copy I can PM it. It's a PDF file so I cannot upload it to this forum.



Is it the same PDF I just posted above? See my last post where I edited it.


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## roberth42 (Sep 26, 2010)

jtp10181 said:
			
		

> roberth42 said:
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No. It's a different pdf file. If you want a copy PM me your e-mail address so I can send it to you.


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## jtp10181 (Sep 26, 2010)

Ok, I am going to start a list of the other materials I see people talking about and thier official documentation I can find. I think we need to gather all this and make a sticky topic!

Permabase: http://www.nationalgypsum.com/submittal/09 28 00-x1.pdf
No non-combustible testing
For 1/2" R = 0.2
FAIL

Wonderboard: http://www.custombuildingproducts.com/docs/data_sheets/1-2 WonderBoard DS.pdf
No non-combustible testing
No listed R value
FAIL

Easyboard (next gen wonderboard): http://www.custombuildingproducts.com/docs/data_sheets/1-2 EasyBoard DS.pdf
No non-combustible testing
No listed R value
FAIL

HardiBacker 1/4" or 500 (1/2"): http://www.jameshardie.com/builder/products_backerboard_halfInch.shtml
HardieBacker® cement board is recognized for use in non-combustible construction in NER-405. 
HardieBacker boards are recognized as non-combustible, when tested according to ASTM E 136.
For 1/4" R = 0.13 
For 1/2" R = 0.26
PASS (All specs equaL to durock)

---

Durock NextGen as a wall shield Install Instructions (courtesy of roberth42)
http://www.megaupload.com/?d=6762U5NF

I noticed in the very bottom right where the official document number should be there is "???-?????"
So I would not consider this an official document from Durock, possibly a work-in-progress that was never finished and posted.


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## nate379 (Sep 26, 2010)

The concrete board that I heated with the torch was glued down to the plywood.  Plywood was fine.  Yes I agree that is not a "scientific" test, but it was good enough for me.

There is no way a log that sits on top of tile is going to heat the concrete board to the temps my torch did.

Now I don't know every stove out there, but that seems more than adequate for most stoves.

I could spend months hmming and haaing over minute details on some PDF, but personally I would much rather have a warm house instead.



			
				Dakotas Dad said:
			
		

> You can hold a torch to it for a week, and it may not even smolder, but IF YOUR HOUSE BURNS DOWN, the insurance company is going to look at every component used, and trust me, you don't want them to find that you used non approved materials.


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## begreen (Sep 26, 2010)

Before this turns into yet another confusing hearth substrate thread, slow down. For example, from the Wonderboard pdf file that is listed I find in that document:
*TECHNICAL DATA
Fire Resistance Ratings UL Rated Report No. 7L30 for floor
protector and wall shield. One-hour rated — non-load-bearing
WHI 6510381.01 7-10-91. Exceeds ANSI A118.9 specifications.
CABO/NES Report NER #447.* 

Yet it is marked "Fail". Why? Any pure cement board product should be fine, no?


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## jtp10181 (Sep 27, 2010)

BeGreen said:
			
		

> Before this turns into yet another confusing hearth substrate thread, slow down. For example, from the Wonderboard pdf file that is listed I find in that document:
> *TECHNICAL DATA
> Fire Resistance Ratings UL Rated Report No. 7L30 for floor
> protector and wall shield. One-hour rated — non-load-bearing
> ...



Its one hour rated, its not a listed non-combustible. If a stove manual says to use it I would go for it if thats what you can get. Quad says to use a non-combustible and I do not see anywhere that wonderboard specifies it is listed as "non-combustible". I think I saw in their FAQ it said it "will not burn" but neither does insulation, it melts.

Would have to look up the ANSI and NER specs they list and see what they are exactly.

They also do not list a R value I could find anywhere, which is a key factor for many stoves.

So I guess wonderboard could be changed to a "maybe"

To be safe personally I would just stick with the products that are specifically tested as a non-combustible.

I need to throw up Micore on the list also. I found this really nice big list of R values the other day also, would be a good wiki article I suppose (instead of a sticky thread).

Logically any of the products should be fine, but if they are not specifically tested as a non-combustible and the stove mfg does not specify that particular product you could be asking for trouble down the road. Now if some insurance inspector wants to get that technical then they really don't want to pay out and maybe you need a new insurance company, but its possible.

I was more excited to find the Durock NextGen info, since that's the stuff we always use. Now if this nextgen stuff crumbles apart like the original durock maybe I should switch to HardiBacker.


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## begreen (Sep 27, 2010)

Maybe I read that differently, but for me those are two different statements. It meets the hearth floor protector requirements. And it meets 1 hr rating requirements. The concerns about it's r value are secondary, though also documented if you visit their website for more details. Many Quads just require ember protection, right? The original Wonderboard cement board has been approved and used for hearths for many years. Why the current concern?

As far as the original Durock crumbling apart, what is being done to it? I have abused the heck out of a partial sheet, now standing outdoors for a couple years, and it is still fine. Has Hardibacker been approved by the same standards for hearth use? This is a pretty confusing post.


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## begreen (Sep 27, 2010)

Info on Durock NextGen from roberth. Looks like it endorses use as a floor protector and provides directions on how to use it for a stove. Seems like USG needs to talk and educate it's support people on the current status of products better.


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## jtp10181 (Sep 27, 2010)

Yes I think you are right, when I look in the PDF it seems "Fire Resistance Ratings UL Rated Report No. 7L30 for floor protector and wall shield." is its own statement.

It is funny they do not mention it for use a floor protector anywhere else in the document, nor the R Value. They also do not show where one can view this supposed UL Report 7L30. Overall I find that the information for wonderboard is vague and disorganized.

The durock comes apart when you try cutting it with anything but a diamond blade saw. And when you use a wet saw it turns into a wet noodle (so to speak).

About the Hardibacker as a hearth use. I read about this in another thread (in regards to durock) and it very much makes sense. None of this stuff really should be UL listed as a fireplace hearth, because that is not what it is meant for. By itself it should not be used a fireplace hearth. I mean this literally, you should not just slap down 4 piece of durock and set a stove on it. You need other materials to create a full hearth "system". It is this end result that would qualify as a hearth or floor protector by UL. There are drop in place UL listed floor protectors, they are made the same way every time and can be purchased pre-assembled. 

Post in reference: https://www.hearth.com/econtent/index.php/forums/viewthread/58597/#666780

Here is the important part, in reference to Durock, and it makes total sense: _he said the old stuff and the new stuff is not allowed or designed to meet that UL spec by itself, but rather it is intended to be “part of an assembly.”_

Now all the other stuff in that post I take with a grain of salt, any figures or facts that cannot be verified on a document are not worth anything. It is great that Jake called all those places to see what they would say. I like how the Hardibacker rep said there is no R value, but I easily found it on their webpage.

*I would say all we can really do is gather all the facts and let people make their own decisions. Every stove mfg will be different with their verbage. All you can do is try to meet or exceed what the manual states for your stove.*

BTW all Quads have required a specific R value as long as I have been around (6 years).

Seems woodstock says (from the OP) to use "an approved non-combustible" and then goes on to recommend Wonderboard, which I cannot find any documentation that it is in fact tested as a non-combustible material.

Yes, this post is confusing, but only because there are little standards on a lot of these subjects so we are left to figure it out on our own.


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## begreen (Sep 27, 2010)

Spot on. Manufacturers don't often provide the material info in the installation docs.  I think I found the R value in the material data which I guess is logical. I notice that the Durock NextGen info that Roberth provided me did not have R value info either, but it is listed in their material data. 

I don't mean to knock Hardibacker, but afaik they use cellulose instead of perlite in their product and I never have found information from them endorsing use for a hearth floor protector. So I shy away from recommending that product. 

Quad installation docs in general are very good, but in the matter of floor protection, they are lacking IMO. They use ambiguous terms like millboard and just needs ember protection instead of listing specifics. For example:
A. Hearth Protection Requirements
FLOOR PROTECTION: Floor protector must be non-combustible
material, extending beneath heater and to the front,
sides and rear as indicated. The floor must be non-combustible
or otherwise adequately protected from radiant heat
given off by the unit and from sparks and falling embers. A
layer of thin brick or ceramic tile over a combustible floor is
not sufficient.
In US installations, it is necessary to install a floor protector
of a minimum of 3/8 inch (9.5mm) thick metal clad millboard
or equivalent a minimum of 16 inches (406mm) in front of
glass and 8 inches (203mm) to both sides of the fuel loading
door. Open the door and measure 8 inches (203mm) from
the side edge of the opening in the face of the appliance.

This is part of why the topic of "what does my hearth require?" comes up frequently. Quad and other stove makers really could help by providing more detailed documentation in this area.


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## jtp10181 (Sep 27, 2010)

That is from an older Quad manual, any newly revised ones will say this:

_In US installations, it is necessary to install a floor protector of a minimum of 1 inch (k value = 0.49, R value = 0.59) of non-combustible material a minimum of 16 inches (406mm) in front of glass and 8 inches (203mm) to both sides of the fuel loading door. Open the door and measure 8 inches (203mm) from the side edge of the opening in the face of the appliance._

I would like to say I contributed to this change, although I cannot verify that statement. I did have a discussion directly with one of the people who writes the manuals though.

As for the millboard, you can find reference to that in the old Durock wall shield instructions I posted earlier.

_DUROCK Cement Board may also be used as a floor protector in place of one layer of 3/8" thick millboard.*
*Having a thermal conductivity of k ² 0.84 Btu in./(ft.2 h °F) in the minimum dimensions specified by the room heater/stove manufacturer._

Although I always thought you needed 1" of durock to meet the same R as the good old "millboard" spec. Someone else can do that math. I have gone through college calculus classes and the R / k value calculations still confuse me every time I try to figure one out.

Oh and about the Hardibacker, as I posted earlier, they specifically have passed the "ASTM E 136" non-combustible test. It will not burn.


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## firefighterjake (Sep 27, 2010)

My head is still spinning . . . 

So the Cliff Notes version is ________________ (please fill in the blank with product) is approved (___ and) (___ but not) (Please check one) listed for floor protection for wood burning appliances.


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## jtp10181 (Sep 28, 2010)

Off the record I would say any of the ones listed are fine.

As a professional, I would have to say only the ones that are specifically tested as a non-combustible material should be used. It also happens that those ones have a slightly higher R value also, which is an added benefit.


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## mkinsley (Mar 2, 2014)

FYI I know I am late to the party but I went here looking for information prior to building a hearth and wanted to see what everyone thought of DuraRock Next Gen.   I would like to add for any other late comers that I bought some today in NJ 8 pieces of 3x5x1/2 and the sticker states its UL Classified in also in accordance with ASTM E136 Standard Test Method for Behavior of Materials in a Vertical Tube Furnace at 750 degrees C.   That's hot.  So I am thinking I yeah there is going to be some heat transfer.  But I intend to use steel studs under the board to give 1.5 inches above my floor and give air flow.  I intend to use double 1/2 Dura Rock Nex Gen board and then a tile upper.   I cant see that failing.


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## NVHunter (Mar 2, 2014)

mkinsley said:


> FYI I know I am late to the party but I went here looking for information prior to building a hearth and wanted to see what everyone thought of DuraRock Next Gen.   I would like to add for any other late comers that I bought some today in NJ 8 pieces of 3x5x1/2 and the sticker states its UL Classified in also in accordance with ASTM E136 Standard Test Method for Behavior of Materials in a Vertical Tube Furnace at 750 degrees C.   That's hot.  So I am thinking I yeah there is going to be some heat transfer.  But I intend to use steel studs under the board to give 1.5 inches above my floor and give air flow.  I intend to use double 1/2 Dura Rock Nex Gen board and then a tile upper.   I cant see that failing.




I'm with you. I'm going to build my hearth almost in the same fashion as you. 3/4" plywood with 1/2" Dura Rock Nex Gen on top of it. I'm going with 1/2" slate tile on top of that.  No metal studs though, just regular 2x4" studs.

Lopi Cape Cod's manual states:


"Floor Protection Requirements


  Floor protection must extend to the sides, rear, and front of the stove (see “Clearances” below for minimum floor protection).


  Floor protection must be non-combustible and at least .018” (.45mm) thick (26 gauge). "

So, with that said, I think my material is 1" plus of non-combustible in material above the 3/4" plywood and well over the .018" thick requirement Lopi requires in their manual. 

I think this sound do. 
If I get spooked then maybe I'll double up on the Dura Rock sheets to two, for an 1" thick base...


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