# Hearth pad being built, R-value required 1.2, no micore in sight



## Highbeam (Jul 12, 2007)

I am building the pad for my Hearthstone and it requires a 1.2 Rvalue. I want the pad as low as possible since it is in a small room and I want max chimney height. Subfloor is wood and reinforced but the stove is heavy and many of the hearth building materials are also heavy. The pad will be 6 feet wide by 4 feet deep and tiled. I like extra big hearths vs. premanufactured ones.

Micore you say? Great idea...

So I have contacted the stove shops, the manufacturers of hearth pads, the building supply outfits, and even the listed distributors for micore in my state. Unless I want to buy a pallet of it then there is no micore available in the state. Most folks, even stove shops, think I am crazy. "Micore? What's that?" I have read through several threads and finding the stuff seems to be tough everywhere but impossible here.

As I go down the list of accepted materials I find gypsum or plaster board. I assume that sheetrock with its combustible paper does not qualify as gypsum board in this application. So is there a more common name for the gypsum board? The R value is only 0.45 but that is twice as high as durock at 0.20. So it is not out of line.

6 layers of durock will get heavy, tall, and just bulky to deal with but it might be my only choice. 

Does anyone have any ideas or even better would be a puget sound source for micore?


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## BrotherBart (Jul 12, 2007)

Go to an office furniture bankruptcy sale. Nobody ever believes me but the primary use of Micore is the substrate for cubicle walls. Most of the time they have to pay people to haul off office cubicles. It deadens sounds and meets the fire codes.


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## jqgs214 (Jul 12, 2007)

many "cement boards" are gypsm


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## jtp10181 (Jul 12, 2007)

There are some fireside stores in California, they could definetly get you some "HX4" board which I belive is very similar to micore 300. We get it in bundles of 5, but they should be using it for thier installs and have it on hand already. I think the sheets are somewhere near 20x60.

http://www.fireside.com/

They might be willing to ship them out to you.


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## Highbeam (Jul 13, 2007)

I emailed a few times now with the USG folks that make micore and they are not surprised that I am unable to find it instate. Out of state or even mail order is not on the path of least resistance so I am to the point now of looking at alternatives. The charts also list "horizontal still air" as being dang effective. So I assume the metal stud hearths detailed on this site took advantage of the air space for the R-value. Does this air space need be be ventilated such as a rear heat shield does? Or can it be sealed up? I am trying to avoid a huge stack of durock for fear that my floors aren't up to the task. This pad will be 4x6' and the beams underneath don't benefit much from distributing the weight.

Can I seal up my hearth pad "air gap"?

Oh and are the metal studs available in sizes other than 2x4? are they structurally sound laying on the ground so that they are only 1.5" tall? Thanks for your help on this folks


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## BrotherBart (Jul 13, 2007)

Highbeam said:
			
		

> I emailed a few times now with the USG folks that make micore and they are not surprised that I am unable to find it instate. Out of state or even mail order is not on the path of least resistance so I am to the point now of looking at alternatives. The charts also list "horizontal still air" as being dang effective. So I assume the metal stud hearths detailed on this site took advantage of the air space for the R-value. Does this air space need be be ventilated such as a rear heat shield does? Or can it be sealed up? I am trying to avoid a huge stack of durock for fear that my floors aren't up to the task. This pad will be 4x6' and the beams underneath don't benefit much from distributing the weight.
> 
> Can I seal up my hearth pad "air gap"?
> 
> Oh and are the metal studs available in sizes other than 2x4? are they structurally sound laying on the ground so that they are only 1.5" tall? Thanks for your help on this folks



It seems one could use ceramic fiber blanket insulation between the studs to gain a bunch of R-value also. It is available at kiln shops, on eBay and such.


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## babalu87 (Jul 13, 2007)

Too bad some of you werent closer
I have plenty of Micore left over, I guess I take for granted how easy it is for me to get it locally.
When I picked up my sheet there was a broken corner on it so the warehouse worker gave me another piece with a sample cut out of one corner. Ended up with pretty much two full sheets and have enough to do two more hearth pads.


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## begreen (Jul 13, 2007)

Good suggestion BB - http://www.thermalceramics.com/home.html
and on eBay there are some of the firebrick sheets on sale. However, I haven't been able to find the R or K value of the product yet.

If no alternative, metal studs + dead air space + 2 layers of durock should get you there. DonCT made his hearth this way. 

https://www.hearth.com/econtent/index.php/forums/viewthread/1837/


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## webbie (Jul 13, 2007)

Bab, what type of supply house did you find yours in?

I have found that drywall supply houses often have strange types of hi-temp insulation, although I am not certain about Micore.

Does McMaster-Carr sell it - they are mail-order.....

http://www.mcmaster.com/

Search for insulation or millboard........

But you can probably find something similar local.

Does HearthStone sell a bottom heat shield? (additional to any that might exist on it already)


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## Highbeam (Jul 13, 2007)

Don's installation inspired me to all but settle on an air gap with metal studs as my main R-value getter. Per the hearthstone manual- horizontal air space gives 0.92 per 1/8". The key thing that I need to be reassured of is that the air space can be static and does not need to be ventilated in any way. Just as in Don's install, I want to tile in the skirt of the elevated hearth. 

So (3.5"/0.125) * 0.92 = 25.76 R value for the air gap. Plus 0.2 for a single sheet of durock. Heck just round this up to R value of 26. 

Go big or go home.


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## Highbeam (Jul 13, 2007)

No additional heat shield available for the bottom of the heritage. There is a cast iron ashpan there already. I bought the rear heat shield to get my clearance to combustibles out back down to 7".


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## webbie (Jul 13, 2007)

With that much excess R factor, I would feel safe without ventilation - but I might use two sheets of the durarock just for making the hearth firm. One layer of it spanned over studs would be subject to movement (and cracking of the tile, etc.).

Strange, but I have seen UL approved stoveboards that are thin sheet metal over one layer of fuzz (like veggie or sound board). I have also seen UL approved mats which use gypsum and then a layer of ceramic tile on top. 

In terms of rules of thumb, keep this in mind. The high requirement for that stove probably related to the ash pan castings that hang down. When they test the stove with firebrands (dry sticks stapled crosswise), you can bet that there is no layer of ash on the grates and also that the ashpan is probably empty. That means the intense heat radiates downward without anything stopping it.

In the real world, things work differently. You will be using cordword, there will be ash on the grates and chances are that the ashpan will usually have some ash in it. I would be very surprised if that hearth hit over 200 degrees on top - whereas in testing it probably hit 500 degrees plus (maybe more).

I did once start a fire with an improper hearth - way back in WV at the same time we burnt the shed down with the sauna stove. We needed some heat and the house had a fireplace....but the hardware store tin stove would not fit into the opening to vent. So we took the legs off of it, and sat the bottom of the oval sheet metal stove directly on a stoveboard which was on the small hearth and projected onto to hardwood floor that was flush with it.

Well, a few days of firing the stove and we started smelling something burning.......you guessed it, we ripped the stove out and the floor was charring! Of course, this was ZERO clearance with the sheet metal of the stove sitting on an el cheap stoveboard........yes, an airspace works wonders.


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## Highbeam (Jul 13, 2007)

It's amazing that we keep using or caring about micore when an air space is so much more efficient (both in thickness and cost) at giving us R-value. The hearthstone folks did confirm with me that the air space does NOT need to be ventilated and that supports are allowed within the air space whether metal studs or any other noncombustible material that will support the weight. This would indicate that if a guy were to cut 2" wide strips of 1/2" thick durock, lay them down on the subfloor in rows on 12 or 16" centers and then laid a full sheet of durock on top of that then an air space has been created with an R value of 3.68.

I still think I'll use the studs for an elevated hearth since I can use the 3.5" air space to route my outside air plumbing.


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## elkimmeg (Jul 14, 2007)

correction Highbeam airspace is a bout .97 per inch not .92 per 1/8" Ever hear of high hats 1.5" instead of a full 3.5" on a 2/4 metal stud you coild keep a lower profile and still get a decent 
R -value Pm me if you need a more detailed description


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## wg_bent (Jul 14, 2007)

Highbeam said:
			
		

> It's amazing that we keep using or caring about micore when an air space is so much more efficient (both in thickness and cost) at giving us R-value. The hearthstone folks did confirm with me that the air space does NOT need to be ventilated and that supports are allowed within the air space whether metal studs or any other noncombustible material that will support the weight. This would indicate that if a guy were to cut 2" wide strips of 1/2" thick durock, lay them down on the subfloor in rows on 12 or 16" centers and then laid a full sheet of durock on top of that then an air space has been created with an R value of 3.68.
> 
> I still think I'll use the studs for an elevated hearth since I can use the 3.5" air space to route my outside air plumbing.



Well, that's how mine is designed.  3 layers of Durock for a hearth surface over metal studs with about a 3" ventilated air space.  Covered with tile.  Actually in front of the stove at the end of the hearth I can feel the thickness of the durock and tile, and the tile gets quite warm, the underside of the hearth is always cool.  personally I think that's a good strategy.


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## Gooserider (Jul 14, 2007)

Wierd coincidence - You are the second person today asking about Micore, and I just posted a link to one of the US distributors with a state by state dealer list over in the other thread earlier this morning.

Gooserider


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## webbie (Jul 14, 2007)

How about a short micore entry in the wiki - goose, can you do it......and put that link?


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## mayhem (Jul 14, 2007)

Nearest Micore dealer/distributor to me when I built my pad a couple months ago was about an hour's drive.  No local building supply stores had any idea what kind of product to sell me so I finally just went shopping at HD...the durarock brand cement board is rated at r=.13 per 1/4 inch thickness.  I wound up using 6 layers under my stove, then tiled over it.


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## colsmith (Jul 14, 2007)

I am surprised that the stove stores near you don't have Micore.  Ask what they use to build hearths when they install stoves, I can't believe they use all those thick layers of Durock all the time.  Micore was recommended to us by one of the stove estimate dudes who came to our house.  We couldn't find it anyplace, so we asked at the store where we were buying the stove.  They don't technically have it for sale, but they use it when THEY build hearths.  They agreed to sell us one 4 x 8 ft. sheet of Micore 300 for about $48.  It was easier than putting down all the sheets of durock we would have needed, so we went for it.  With all that air space it seems like you have less support under the (always heavy) stove, I suppose that is why people aren't all keen on it  Mind you I was a computer engineer not a structural engineer, so what do I know.  

Maybe you asked the wrong person at the stove stores, can you speak to one of their installers and ask again?  The regular salesguy didn't know anything about Micore at our local fireplace store, but the installer was quite knowledgeable (it is his family's business.)


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## Highbeam (Jul 14, 2007)

I asked the three local stove shops and after them telling me they had never heard of micore, I would tell them why I wanted it, and then they would tell me that they use premanufactured pads. None of them actually make the pads, maybe it's a dying art, not as profitable as the pads. The installer that two of the three stove shops use also had never heard of it.

Hearthstone's owner's manual which is online for the heritage clearly calls out 0.92 per 1/8" of horizontal still air. 0.97 per inch also works for me but either Hearthstone has a misprint in a very important part of the manual or they used a different source for their R-calue charts. It wouldn't matter for my install but the inspector would have a hard time looking at my manufacturer's chart and calling BS.

The air gap can be filled with as much necessary support as is needed. Hearthstone authorized steel studs or other material as needed for support. I figure that I will be careful to provide a steel stud directly beneath the final location of the stove legs. 

I of course had no problems finding the micore distributor list but that doesn't do squat for me when the distributors in my state only sell pallets and are not willing to refer me to retailers. An actual list of retail outlets would be far superior.


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## Gooserider (Jul 14, 2007)

Will try to write something up, but no guarantees - there's this big party coming up that's getting a lot of my attention right now...  :coolgrin: 

I don't know what the quality is on those distributor links - it is just one that I found somewhere and bookmarked, figuring I might need it some day, but I haven't actually tried to see if they are useful yet...

As to why Micore instead of an air space?  I think it depends on the design objectives.  Assuming Elk is right about the .97 / INCH value for air space I think Micore still is the champ for the highest R-value per thickness.  

If you are trying to build a hearth that is as close as possible to flush with the existing floor, and you have a stove that requires a high R-value hearth, then I think Micore is the only option that will work as part of the sandwich, Working on the assumption that the floor is typical construction of plank subfloor, 3/4" particle board or ply floor, with carpeting over it, you have about 1-1.25" to work with.  Per the Chimney Sweep's 
R-Value Cheat sheet 1/2" of Micore, 1/2" of Durorock or Wonderboard, and 1/4" of ceramic tile will just fit and give a 1.3+ R-value...  (You could get more by taking out the subfloor to get down to the bare joists, but Elk says that's a bad idea, not sure why...)  I don't see any other options that would get it thinner, or keep the same thickness.

If you are going for a raised hearth, there is no real need for the Micore, as it doesn't offer any major advantage over the air-space or stack of Durorock approach...

Gooserider


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## elkimmeg (Jul 14, 2007)

Goose  one can got to bare joist but they have to replace the load bearing some how I wouls suggest 2/8  2/10 0r 2/12 solid blocking frush with the top of floor joisr between the floor joist spacing. Ususlly this should give you 1.5" to work with for a flush  configuration of the floor.

Of the products out there cement boards  I would opt to work with Hardi Backer board every time . It is much easier to work with, easier to cut.
'
I think a 3'/5' at Home Depot cost about $11 for the 1/2" thickness.

Just checked the website R 0.26 per 1/2"


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## webbie (Jul 14, 2007)

That would be 4 layers for most hearths...really not too bad. As I mentioned before (Elk, correct me if wrong), this stuff is really not designed for spanning distances on floors with weight so at minimum doubling it up (even if R is reached with air space) might be prudent.

Elk mentioned the lower profile metal channels in an earlier post - I think these are what I used for the ceiling in my jam room - very low profile and then even have a small lip where you could screw or nail to floor. They have a wide bottom which screws will cut right into (no drilling).

Available at sheet rock supply specialty places. As I said before, when I visited the local place I was amazed at all the various building materials and insulation that I was previously not familiar with.


Pic of the channel enclosed - pay no attention to the thing which hangs vertically - that is for ceiling hanging. I assume Elk is talking about using this channel upside down (those little flanges) toward the floor.

This stuff is dirt cheap, BTW.


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## begreen (Jul 14, 2007)

I've only used Durock brand board because it is 100% cement with a fiberglass backing. Hardibacker board is fire resistant, but contains 10% cellulose which is I assumed is considered combustible? Elk am I in error? The cellulose content is the same reason our tile setter says he never uses HB board, especially in a wet area.


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## jtp10181 (Jul 14, 2007)

About the wet areas....

_"Hardibacker® is a unique, cement based, water resistant substrate for tiling that can be
used on walls, floors and countertops. Particulary suitable for use around baths, showers and
in kitchens, it will keep your tiles just where you want them. Stuck hard to the surface. Tried
and tested in millions of homes worldwide, Hardibacker® tile backerboard has a 10 year
guarantee, and is easy to cut and install."_

I read someplace, I thought on the hardibacker webpage that it was an approved non-combustible material. But now of course I can't find it... well I found something now.

_"Can I use Hardibacker® Backerboard for fireplaces or barbecues?
No. While Hardibacker® Backerboard is an interior non-combustible product, it is often used with barbecues. It is not a recommended or a warranted application."_

http://www.jameshardieeu.com/pages.php?pages=faq
http://www.jameshardieeu.com/pages.php?pages=products&subpage=hbacker


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## webbie (Jul 14, 2007)

Correction - found this old post by Driftwood:

"Hardy backer is made of cellulose; I called James Hardie technical support 1-888-JHARDIE about the lack of R value off their ½ inch hardybacker product.  They told me ½ inch hardybacker has no Rated R value, “it conducts heat”.  Hardy backer is not the stuff you want behind your stove or under it. WonderBoard or Durock cement boards are R rated and UL Listed for that application. "

Uh Oh.....I hope no one has been using this stuff for hearths, cause I'm gonna make 'em rip them all out!

(Note: They may have other products that we don't know about supplied to HD, etc......there should be a label on them or product info available)


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## babalu87 (Jul 15, 2007)

Webmaster said:
			
		

> Bab, what type of supply house did you find yours in?



Kamco Supply , 6 or 7 locations in the Northeast.


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## webbie (Jul 15, 2007)

OK, yeah they are a drywall type house:
http://www.kamco.com/

I'll have to see if Goose put that wiki entry in and we'll work on it....also get this hardie info up, although maybe we should wait for elk to check the board - it seems strange that the factory rep would say "no R value" when Elk obviously got his from somewhere! Something doesn't match.


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## elkimmeg (Jul 15, 2007)

hardi backer board is r0.13 per 1/4" for specs ccheck out this web limk to conform fire resistande  and r-value

http://www.jameshardie.com/homeowner/products_backerboard_halfInch.shtml

 In comercial construction used in fire rated assemblies is fire retrardent wood and plywood. These products are not fire resistant but damn hard to ignite.
 One can use a mapp torch on this material and only produce a charr area but won't flash into combustion .I know I have applied the mapp torch


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## Gooserider (Jul 15, 2007)

Looks like from the FAQ associated with the page that Elk was pointing to - the official Mfgr spec page for the stuff, like it can be used as a non-combustible.  Elk - I'm assuming the numbers mentioned in the web page are the ones that you would look for as an inspector and / or are the ones called out in the codes?

If so, then I see no real problem, and a possible advantage in that it appears the HardieBacker is available in 1/4" thickness as well as 1/2" - important for those concerned about keeping the total thickness down. 

However this would raise the question as to whether 1/4" HardieBacker over Micore would be stiff enough to avoid cracking under the weight of a stove and human traffic? - once again thinking in terms of the method I've suggested before of cutting out the first layer of subfloor, and putting the Micore over that, then the HardieBacker and tile or other non-combustible hard floor.



> 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.



This brings up another sort of relevant question that I asked a while back, and I don't think got an "Elk - level" answer...  What about "split level" hearths, where the stove itself is on a raised platform that is smaller than the required "hearth footprint" with an extension at a lower level to get out to the required distances.  The extension is at a lower level, thus farther from the stove bottom, and therefore presumably shouldn't need as much thermal protection as it would if it were closer - how much, if any, "credit" does one get for the extra space?

From the earlier thread where I was asking about this



> BeGreen - 12 May 2007 11:39 AM
> 
> Gooserider - 12 May 2007 12:14 AM
> 
> ...


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## begreen (Jul 15, 2007)

You'll note in the specs that hardibacker board has a mold retardant for wet area use. That is not required to the non-cellulose products. I trust my tile guy, he says don't use it except perhaps for vertical surfaces.


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## Gooserider (Jul 15, 2007)

Webmaster said:
			
		

> How about a short micore entry in the wiki - goose, can you do it......and put that link?



Well I'm now working on a LENGTHY "Hearth Design" article - that will include a reference to Micore and the other materials in it, but so far hasn't gotten to that point.  Also I haven't been doing a very thorough job of "wikifying" the text.  It would probably not be a bad thing if folks were to start looking at the article and "fact checking" it, adding additional content, etc...

Gooserider


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## webbie (Jul 15, 2007)

I will do so when I have time - if it ends up being "timeless", I can then even move it to the main articles page, although we cannot edit from there. Another option is to link the relevant main articles to that wiki entry - 

Amazing how much information there is to be had! It's like that old Buddhist saying "Sentient beings are numberless; I vow to save them all..." In our case "The information is limitless, we vow to attempt to write it all down".

BTW, speaking of that, I had fun the other day in the Internet Archive looking at the old hearth.com and also some other sites I did. In fact, I'm gonna ressurect some blog entries that I thought had disappeared - but the wayback machine has 'em.

Now don't spend too many hours there, but type any url into the wayback machine and you can imagine how big of a repository the archive is!

http://www.archive.org/web/web.php


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## webbie (Jul 15, 2007)

I'm with Begreen. I would stay away from Hardi board now that we know this - unless we have some exact proof from the manufacturer which refers to that use. The cellulose and the conversation with the factory (Driftwood) is enough for me. Yes, I agree is does not ignite and has a low flame spread and smoke index, but when alternate UL materials exist which do not have the cellulose....well, I'd use 'em.

As far as just vertical surface, I do believe that their instructions show use on floors and counter tops. I think it would function fine if used as directed. 

Wow, this is really some detail that normal people (only a crowd could research this) would have a tough time with. 

To be clear, I'm with Elk in that the use of it is probably more than safe. But safe is not the standard......Well, time for perhaps a little more digging.


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## Gooserider (Jul 15, 2007)

Webmaster said:
			
		

> I'm with Begreen. I would stay away from Hardi board now that we know this - unless we have some exact proof from the manufacturer which refers to that use. The cellulose and the conversation with the factory (Driftwood) is enough for me. Yes, I agree is does not ignite and has a low flame spread and smoke index, but when alternate UL materials exist which do not have the cellulose....well, I'd use 'em.
> 
> As far as just vertical surface, I do believe that their instructions show use on floors and counter tops. I think it would function fine if used as directed.
> 
> ...



I think this is an application that I would consider safe and suitable if Elk is willing to buy off on it.  Hardie does say it is fire resistant, and acceptable for fireplace walls and heat shielding.  They also specifically list is as suitable for floor underlayment if it is glued to the substrate with thinset or equivalent.  The two should combine, I would think.  HardieBacker may contain SOME cellulose, but their spec sheet says it is "90% Portland cement and ground sand." and later that it's surface fuel contribution is ZERO - That would cause me to assume that any potentially combustible cellulose is buried inside the material, and not present in enough quantity to be a problem

However to be sure, it might be a good thing to have Elk write to them, waving his building inspector credentials, asking them to clarify the use in their FAQ - I'd ask, but I figure that if Elk puts his inspector hat on, they would be more likely to give him a thorough and complete answer...
I'd ask things like:
1. Is it acceptable to use HardieBacker underneath a woodstove as part of a non-combustible hearth?
2. If it is acceptable, is the R-value of .013 per 1/4" still correct?
3. Is it acceptable to stack multiple layers of HardieBacker to achieve required total R-values?  If so, are there any special recomendationd for fastening the layers together?
4. Is it acceptable to use HardieBacker over other types of insulating sheet materials (i.e. Micore) as part of a sandwich design?  If so, is 1/4" acceptable over a somewhat soft material such as Micore or is 1/2" needed?
5. If building a raised hearth with metal studs supporting it, how many layers of 1/2" HardieBacker would be needed to obtain sufficient strength to function without combustible underlayment? (or suggested alternative to the combustible underlayment (plywood)


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## webbie (Jul 15, 2007)

Goose, caution would say that we should work the other way around. Unless Hardi says it is OK for this use, then it isn't. Again, the question is not whether it will work, but whether it meets any listing requirements. Here are the exact words from Dura and WB:

Wonderboard
 "UL Rated Report No. 7L30 for floor protector and wall shield."

Durock
"also adaptable for high-heat areas like fireplace fronts and UL-listed wall shield/floor protectors. DUROCK"

I have not seen any information of this type on the hardie site. There is a big different between fire resistant and approval for hearths. 
I think some of your questions are already answered - some of the sites have guides to the weight bearing capability. R values can always be added together, that is the way it works. 

Hardie does show a smoke generation index of 5, which I assume is because of the cellulose burning. 

Maybe we will hear from them...but will they have a test report like the others and specifically mention it in their instructions? Or will some factory phone person tell us something as silly as the last one "no R value, heat passes right through it". 

Since the other two products are available almost anywhere.....I guess I am questioning why use something without this specific listing? As to use on fireplace fronts, firewalls and such, that is a different application. 

Also, Durock has 30 year interior warranty....I though I saw 10 on the Hardie.

My guess on this whole thing is that it would pass the tests, but they have not submitted it for such. Another one of those thousands of situations that fall between the cracks.


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## elkimmeg (Jul 16, 2007)

Goose that Donor stove in march we installed and ended up 2" shy of 54" above I have James hardi fax my office all the flame spread and asked the
 very questions and concerns you guestioned.  sufecient evidence was produced and acccepted by a very differcult inspector in the neighboring town.
 In the end there was little to question. Not only is it easier to cut but I in full belief it is superior to cement boards reinforced with fiberglass webbing.

 That webbing can melt in less than 800 degrees, the normal melting point of common fiberglass. In reality the heat exposure should never approach that level.  especially faced with ceramic tile of cultured stones. Did you know there are two micore products. One should also check into accostical ceiling tiles rated for fire assemblies..  I believe they are made of micore

I must look into fire rated treated wood and plywood to see if their heat range will allow their use in hearth extentions I have to find out the heat range required for the extentions. Knowing that might open up more alternatives It may be possible to use  common fiber glass packed between layers of hardi backer boards One inch of hvace fiberglass duck wrap is r4.5 and 1.5 " can go as high as R5.5 given the density of the fiber glass


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## Gooserider (Jul 16, 2007)

Webmaster said:
			
		

> Goose, caution would say that we should work the other way around. Unless Hardi says it is OK for this use, then it isn't. Again, the question is not whether it will work, but whether it meets any listing requirements. Here are the exact words from Dura and WB:
> 
> Wonderboard
> "UL Rated Report No. 7L30 for floor protector and wall shield."
> ...



From the HardieBacker FAQ


> HardieBacker boards are recognized as non-combustible, when tested according to ASTM E 136


.  How ASTM E 136 compares to UL 7L30, I don't know.  The FAQ also says it IS acceptable for fireplace fronts.  The message you pointed at earlier in this thread saying it wasn't OK was also talking about BBQ's, and from the context of the quote it appeared the issue was the exterior application, not the non-combustiblity.



> I have not seen any information of this type on the hardie site. There is a big different between fire resistant and approval for hearths.
> I think some of your questions are already answered - some of the sites have guides to the weight bearing capability. R values can always be added together, that is the way it works.



Perhaps, but if you say the other application data is not relevant, then I'm assuming this should be confirmed as well.



> Hardie does show a smoke generation index of 5, which I assume is because of the cellulose burning.


 Possible, the question is what does that number mean in comparison to other products - what is the SGI for Durorock and Wonderboard for instance?



> Maybe we will hear from them...but will they have a test report like the others and specifically mention it in their instructions? Or will some factory phone person tell us something as silly as the last one "no R value, heat passes right through it".
> 
> Since the other two products are available almost anywhere.....I guess I am questioning why use something without this specific listing? As to use on fireplace fronts, firewalls and such, that is a different application.
> 
> Also, Durock has 30 year interior warranty....I though I saw 10 on the Hardie.



Hardie appears to be a lighter weight product, and be easier to work with (or so Elk says)  It is available in 1/4" or 1/2" thickness, the others appear to be only availale in 1/2".  It has a slightly higher R-value (0.260, vs 0.200 for the others) it claims higher strength than the others.

HardieBacker's Website says it has a 20 year transferable warranty, although reading it I would not consider it a highly valuable sales point - it's only good for the cost of the product, and is pro-rated so the amount drops every year, and (like lots of warrantees) is loaded with tons of exceptions and loopholes.  I'd expect the others to be similar.

[/quote]My guess on this whole thing is that it would pass the tests, but they have not submitted it for such. Another one of those thousands of situations that fall between the cracks.[/quote]

Perhaps...  They also may not have realized that this is an important enough market segment to put the data on their website.

Additional data - pulled from the Donor stove install where Elk failed the first inspection because of a missed clearance and fixed it with HardieBacker - Granted, this was overhead and not underfoot, but...

"I must say Hardibacker board is much easier to work with that cement board lighter and cuts better 

Thermal Values (ASTM C177) 
1/4” HardieBacker and 1/4” HardieBacker EZ Grid® cement board Thermal Conductivity: k-value 7.80 Btu/ft2 x h x °F 

1/2” HardieBacker cement board Thermal Conductivity: k-value 20.07 Btu/hr-ft2 - °F 

1/4” HardieBacker and 1/4” HardieBacker EZ Grid® cement board Thermal Resistance: R-value 0.13 ft2 x h x °F/Btu 

1/2” HardieBacker cement board Thermal Resistance: R-value 0.05 hr-ft2 - °F/Btu 

Non-Combustibility 
When tested in accordance with ASTM Method E-136, HardieBacker cement board is recognized as a non-combustible building material in NER-405. 

Surface Burning Characteristics 
When tested in accordance with ASTM method E-84: Flame Spread – 0, Fuel Contributed – 0, Smoke Developed – 5. 

Fire Rated Assemblies 
Hardibacker cement board may be used as a component in one-hour fire-resistive wall construction; consult NER-405 and Intertek-ETLSemko website listings for recognized assemblies, or contact James Hardie’s Technical Services at 1-800-9HARDIE (1-800-942-7343).

At any rate, I'm sending an e-mail to Hardie Tech support, will see what they have to say.  In the meantime I've added a blurb to the Wiki Article saying that there are questions about the suitability of HardieBacker and it is not currently reccomended.  (BTW, I need some help getting the table of materials in it right - looks fine when I'm in edit mode, but looks like CHIT in the display mode...)

Gooserider


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## DonCT (Jul 16, 2007)

If you don't mind the raised hearth look, the way I constructed my "Pad" is solid as a rock.

There are sooo many ways to meet R requirements that you can get pretty creative. Don't have Micore? Do a Durock sandwich.


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## Gooserider (Jul 16, 2007)

elkimmeg said:
			
		

> Goose that Donor stove in march we installed and ended up 2" shy of 54" above I have James hardi fax my office all the flame spread and asked the
> very questions and concerns you guestioned.  sufecient evidence was produced and acccepted by a very differcult inspector in the neighboring town.
> In the end there was little to question. Not only is it easier to cut but I in full belief it is superior to cement boards reinforced with fiberglass webbing.
> 
> ...



This sounds excellent, Elk, I would love to see more research into alternative methods of getting non-combustible hearth structures.  However I don't know enough of the code's "alphabet soup" standard references to tell what is meaningful and what isn't.

A couple of suggestions I'm still not sure about is something I asked about a while ago, and you never got back to me on, is whether it would be structurally acceptable to replace part of the 3/4" subfloor decking with a thinner non-combustible alternative.  I know you had suggested replacing the decking w/ 2x? blocking flush with the joists but that sounded like a difficult job.  What about replacing the wooden decking with something like 1/8" steel or aluminum plate?  I would think that would be as strong or stronger, do the same job of stabilizing the joists, and act as a heat dissipating shield under the pad...

The other is the "split level hearth" question I mentioned earlier in this thread - If dead air space is worth R-0.970 per inch, does the same thing apply to open air?  If so, it would seem like almost any flush extension to a raised hearth would be compliant if it was non-combustible - even just tile over ply, or maybe tile over one layer of cement board...

Gooserider


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## elkimmeg (Jul 16, 2007)

goose the ASTME  136 standard  materials  must with stand 1200 degree heat before the break down or failure.  This is the same standard of draft stop caulking.

 Boss 136 has been tested to 3000 drgrees Dap tested to 2300 degrees and the 3m brand 136 1200 degrees 
To meet that standard it with stands more heat than ever exposed to wood stoves. If there is 1200 degrees the floor around it would burn threw first


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## webbie (Jul 16, 2007)

Ah, Goose, I did a bit of spell check and got that table looking good the only easy way.....took a screen shot of it in text editor and now it is a graphic - looks pretty good, though. Thanks for the effort - I will definitely link to it from our existing clearance articles.

https://www.hearth.com/econtent/index.php/wiki/Hearth_Design/

I'll eventually put some pics and scans in there also, to dress it up a bit. We can even link it to some hearth construction pic and threads that are in the forum pictures areas.


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## begreen (Jul 16, 2007)

Goose, given that the cost difference is negligible, why would one choose anything but the best for the job, no questions asked?


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## ansehnlich1 (Jul 16, 2007)

3/4 inch advantech subflooring, then 4 sheets durock, then brick, then Jotul F-500


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## Highbeam (Jul 16, 2007)

DonCT said:
			
		

> If you don't mind the raised hearth look, the way I constructed my "Pad" is solid as a rock.
> 
> There are sooo many ways to meet R requirements that you can get pretty creative. Don't have Micore? Do a Durock sandwich.



As you did Don, I intend to borrow heavily from a design on this site. Yours. Not so much in shape but I intend to steal your construction method with the studs and durock. I won't use any sheetrock though.... I had planned and desired a low hearth to keep it out of the way but once I concluded that I must elevate the hearth, then I may as well take advantage of the extra structure of the metal studs. Heck, we may even enjoy the stove being a bit higher from the ground. More at eye height, easier to load, etc.


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## begreen (Jul 16, 2007)

There ya go! Have fun and  take some pictures!

What are you going to use for the top surface of the hearth?


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## webbie (Jul 16, 2007)

Please see this thread for my current opinion and questioning of air spaces in hearth constuction:

https://www.hearth.com/econtent/index.php/forums/viewthread/8320/


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## Gooserider (Jul 16, 2007)

Webmaster said:
			
		

> Ah, Goose, I did a bit of spell check and got that table looking good the only easy way.....took a screen shot of it in text editor and now it is a graphic - looks pretty good, though. Thanks for the effort - I will definitely link to it from our existing clearance articles.
> 
> https://www.hearth.com/econtent/index.php/wiki/Hearth_Design/
> 
> I'll eventually put some pics and scans in there also, to dress it up a bit. We can even link it to some hearth construction pic and threads that are in the forum pictures areas.



I agree, the table does look MUCH better now - the only question is how hard will it be to edit the table in the future?  I'm hoping that over time we might be able to add more materials to the table, or get better sources and "official" values for the materials listed - I might trust Tom, or the folks on the forum, but numbers credited to them are not going to be as convincing to Elk's buddies as a Mfgr website or published standard listing.



> BeGreen:
> Goose, given that the cost difference is negligible, why would one choose anything but the best for the job, no questions asked?



Agreed, but define "best"?  I'm seeing glowing reccomendations for HardieBacker from Elk, and claims from the Mfgr website (which I do take with a grain of salt) about how HardieBacker is superior to other forms of cement board, so one could argue that it IS the best...  I'm trying to resolve that.

One of the constraints that I'm operating under in designing my hearth extension is that raising the level is NOT acceptable, as I want to keep that part of the floor useable for other things when we aren't running the stove.  Now examining the manual for the Defiant Encore 0028, it does not have extreme R-value requirements, but I do believe in following my own advice on overbuilding to accomodate possible future stove upgrades, and want to make sure the extension has as high an R-value as I can reasonably get.  That pretty much means Micore, some form of cement board, and tile or stone.  I'm not sure if I'll want to remove the decking to get the extra space or not, I think I will make that decision if I'm ever able to figure out what is under the bricks on the existing hearth - I get no benefit from exceeding the existing hearth's construction with the extension. 

Gooserider


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## Highbeam (Jul 16, 2007)

BeGreen said:
			
		

> There ya go! Have fun and  take some pictures!
> 
> What are you going to use for the top surface of the hearth?



The wifey and I are choosing between slate and slate looking tile. The same tile will be used for the doorway to the front door and maybe also some countertop backsplash so I am leaning away from slate for fear the dark "dust" of it will be tracked into the house as is discussed on the John bridge tile site. Plus being a first time tiler I would prefer the ease of installation of plain old ceramic tile. The wall behind the stove is plain painted drywall at least 7" away. Maybe in the future we'll stick tile to the wall but for now just paint.

I will try and provide a similar step-by-step as Don did. Same stove, similar hearth design, and similar tile. The top front corner of the tile is going to be a challenge. Some folks like Don let the horizontal tile hang over but I want the corner to be a plain 90 degree one. Anyway, I'll fumble through it. I look forward to learning this skill.


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## begreen (Jul 16, 2007)

Avoid Home Cheapo slate. It will flake regularly and make a constant mess. There is a fabulous world of tile and stone out there. Lots of choices.


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## elkimmeg (Jul 16, 2007)

I'll second do not buy tile from home cheapo A customer picked out the tikle I installed in her bathroom there were spmany chips of the ceranic coating I had to rip it all out and start over
 Home Cheapo sell  crap seconds in tile. I will never buy tile from there again  And while I'at their bher paint sucks too poor coverage poor color pigmentation and has the dendency of lifting

Another product I will never buy there again


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## Highbeam (Jul 16, 2007)

Thanks for the tip guys, I happen to live within walking distance of the HD here so frequently stop by there on route to other places. It has been very handy but I had no idea that there ceramic tile was also a bad purchase idea. We have some floor specialty stores that sell nice tile but I want to be sure not to find some rare stuff that I can't replace in the event of a cracked tile. I will buy extras for sure. A pretty small tile purchase so I can afford to use a higher priced tile. I need to buy it soon so that I can do the layout and build the hearth to match the tile size.


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## elkimmeg (Jul 17, 2007)

Tip highbeam rent a wet saw to cut your tiles  the end results will look so much more professional

Tip two purchase plastic spacers  If using square tile the mark the center lines so that all edges have even mangins  
do a dry run placement with the spacers first to see the mag rgin differences. If that does not work out then can you add to the platform or design the platform to match the tile size

 It might pay to purchase the tile and lay it out  before building the hearth remember there is no, penalty for exceeding requirements just an added safety margine.

PS latest NFPA 211 now requires 18" in front of loading doors not 16" That change occured in the 2006 edition


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## Gooserider (Jul 17, 2007)

elkimmeg said:
			
		

> Tip highbeam rent a wet saw to cut your tiles  the end results will look so much more professional
> 
> Tip two purchase plastic spacers  If using square tile the mark the center lines so that all edges have even mangins
> do a dry run placement with the spacers first to see the mag rgin differences. If that does not work out then can you add to the platform or design the platform to match the tile size
> ...



Actually what I've heard some suggest is that rather than renting a wetsaw, one get one of the HF cheapies, use it for the job then sell it on E-Pay - total cost less than the rental, no worries about rushing through the job in order to get the saw back in time, etc...  The HF tool may be a junker for long term use, but it should last long enough to use it and pass it on to some other [strike]sucker[/strike] purchaser.

On the NFPA 211 change, does that now mean that US and Canadian setups will have the same value?  If so I need to change the Wiki article.

Gooserider


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## Highbeam (Jul 17, 2007)

For crying out loud, the requirement is 18" now? I feel like a canadian at heart eh so that's okay. I had planned for that and even a little more than 18" as I was going to shoot for 18" from the front of the ash lip but cripes, I would have been pretty upset if I did my best to use the manufacturer's specs and picked 16". Then even more ticked off if I had used the 0.92 R value per 1/8" of air space only to find that that was also in error.

Thank goodness for this site. 

I'll take a look at the HF saw too. I will pick up the tile and spacers before even buying the metal studs. I want to minimize the cut tiles.


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## Highbeam (Jul 25, 2007)

Okay, the steel studs are in. I used a lot of these studs since they felt really flimsy and with lots of studs came lots of machine screws so lots of little high spots to set the durock on. I set the durock on and screwd it frequently to the stud flanges. Then cut the side skirts and screwed them to the sides of the studs. 

Steel studs are not very strong. The durok for the skirt was especially bad about not being rock solid since it floats around as the web of the steel stud flexes. Securely screwed these things aren't solid like a wood stud. 

I taped and mudded the seams just as I would do a sheetrock job but using special mesh tape and mortar. Then lscrewed down the second layer or durock with stagerred seams and a full bed of mortar applied with the notch trowel. This really made things stronger. The steel studs allow some creeks and noise but I hope that the weight of the stove, tile, and more mortar tighten things up. 

The durok is great to work with using an abrasive wheel on my circular saw. Very predictable but heavy. The steel studs were hard to find. Not at HD or Lowes, a Mclendons hardware store had them after calling several other hardware stores. 

The hearth looks big now. I mudded all the seams on the top and the pad is starting to look solid now. 

I checked for level and everything is spot in in both directions. I have pictures at home for the inspector.


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## babalu87 (Jul 25, 2007)

Not running the flag up the pole for Home Deep-ho but I have used their wetsaw on two jobs using porcelain tile and it still in great condition.
I second buying one and then re-selling...... though I have never re-sold a tool in my life and rarely borrow tools, I just get it if I need it.


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## Highbeam (Jul 25, 2007)

I have the regular old tile snapper in hand right now. I am learning by doing here so I have designed my pad for only straight cuts in places that are concealed. It's just a big rectangle, nearly 4'x6'. The tile is labeled as porcelain but it has a base material and then a glaze so that it looks like a ceramic. I don't know but in reading the porcelains are known for better strength and durability.

I will do some practice snapping tonight.


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## rodstabile (Oct 1, 2007)

Micore 300:


Mantels Direct - http://www.mantelsdirect.com/s.nl/it.A/id.52283/.f?sc=18&category=304


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## Highbeam (Oct 1, 2007)

"For items shipped via freight carrier to residential addresses, a $65 fee will be added to your order. There is no charge for delivery if we can deliver to a commercial business address not in a residential area or if the mantel can be picked up at a nearby freight terminal."

It'll be pricey but it is a source. Good detective work Java.


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## michaeldd (Jan 2, 2011)

Hello All,

I've been lurking for a while gathering information, making plans, finding new info, revising plans...   ad infinitum it seemed at times.  The time has finally come when it has all nearly reached a finish.  The hearth is built, my VC Defiant I stove is in place, and the house is warmer!  Thank you all for your valuable help.

Here is what I did...  

I had problems gathering some firm information about the R values for my stove so I made the best estimation I could adding what I thought were decent safety margins.  I did the same for wall clearances since the Defiant I manual wasn't all that clear and I was unable to get a copy of the Installation and Planning Guide from VC.

Originally I planned for a hearth that would have given a wall clearance of 36".  When I laid that out on the floor I found it blocked most of a doorway and a window...   ok, so no go.  Back to more research.   My stove came with a rear shield, and with proper wall shielding I could reduce clearances to nearly 12".  Ok, that could fit and for good measure I gave the stove 16" clearance from the wall placing it angled toward the room, 45 degrees to the walls.  The hearth ended up at 68" x 68" with the corner extending into the room clipped at 45 degrees and 20" out from the stove front.

With planning finished I started construction by stripping the carpet from the floor and:
1.  One layer of 3/4" exterior plywood nailed down with 1 1/2" galvanized roofing nails.
2.  One layer of 1/2" Micore 300.
3.  One piece of 24 ga aluminum which extended to within 4" of the edges.
4.  Two layers of 1/2" Durock.
5.  One layer of bright white 6" x 6" tile.
6.  Four bricks of 8" x 8" x 4" size under the feet of the stove.
7.  One sheet of 24 ga aluminum sized to fit under the stove, on top of the bricks.
8.  Flex-bond between all layers.
9.  1" galvanized roofing nails used on all layers from the Micore 300 and up.  I thought 1" would secure each layer to the one below, but help prevent heat transmission to lower layers.

When working on the placement of the layer pieces I'd first thought to cut a 4' wide pieces, as long as would fit, then cut other pieces to fit the remaining space, rotating the layers so seams were not one on top of the other.  I didn't like this because I always ended up with a bunch of small pieces cut to fit the increasingly smaller gaps.  Then I had an idea...   what if I cut a 4' x 4' square of material and placed it in the center like a diamond with the points reaching out to the corners.  wonderful!  In a stroke of great fortune the hypotenuse of a right triangle with two 48" sides was 68", the exact length of the hearth sides!  Now the seams wouldn't lie one above the other...    one layer with a 48" square diamond in the middle, then the next with four triangles with the points in the center.  To make it easier to visualize, try to picture this: firstly cut one 4' x 8' sheet into two 4' x 4' pieces.  One of these is placed in the center.  Cut the remaining square into four triangles to fit the remaining corners of the hearth.  Secondly cut a 4' x 8' sheet into two 4' x 4' squares, then cut each square into two triangles resulting in four triangles dimensioned 48" x 48" x 68".  These were placed on the hearth with the 68" edge on the outside of the hearth and the points in the center.

I realize some of this is over engineering it a bit, but lacking in hard data I decided to make SWAGs that erred on the side of caution.  I've read that an aluminum layer, while once required, is no longer, but I decide to include it anyway, terminating it well away from the edges to prevent any heat from making it to the edges of the hearth and it's wood trim.

The stove sits on top of four bricks that are raised above the top of the tile by approximately 3 1/4", thereby lessening radiation gain some more.  On top of the bricks, and beneath the stove, I placed a sheet of 24 ga aluminum as an additional heat reflector.  I also used bright white tile to reflect as much heat as possible vice absorb it.

I have started placing Durock on the walls which will eventually extend 8' up from the hearth surface. Eventually I'll add tile to it as well, perhaps with a mosaic of Prometheus bound in chains with the great eagle feeding on his liver...

I've attached a photo of the nearly finished installation.  The wood you see on the hearth is drying from the recent snows, it will be moved shortly.  Nothing will be placed on the tile for the long term.

I'd be happy to hear your thoughts, comments, etc.


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## begreen (Jan 2, 2011)

Welcome Michael. Good to see your progress. Can you start a new thread on this topic so that we can follow your work exclusively? 

I think you can lose the top brick and heatshield aluminum. Clever solution, but you are adequately covered by the nice hearth. One thing to check though, the Defiant needs large clearances. There should be 36" between the load door opening and the wall. The walls look like they might need wall shields and the curtain should go. 

PS: The manual for older VC stoves is posted in two parts here:
https://www.hearth.com/econtent/index.php/wiki/Vermont_Castings_Older_Stove_Models/


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## tjwarren (Jan 2, 2011)

[quote author="Highbeam" date="1191268005"]"For items shipped via freight carrier to residential addresses, a $65 fee will be added to your order. There is no charge for delivery if we can deliver to a commercial business address not in a residential area or if the mantel can be picked up at a nearby freight terminal."

It'll be pricey but it is a source. Good detective work Java.[/quote

That's where I ordered from and it's was free shipping to my door. I just clicked on the link and added to cart md it says the same thing.I also have found on Ebay


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## Highbeam (Jan 2, 2011)

Holy old thread batman. 

Michaeldd, your post deserves its own thread. 

Thanks for the blast from the past.


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## Renovation (Jan 2, 2011)

elkimmeg said:
			
		

> Goose  one can got to bare joist but they have to replace the load bearing some how I wouls suggest 2/8  2/10 0r 2/12 solid blocking frush with the top of floor joisr between the floor joist spacing. Ususlly this should give you 1.5" to work with for a flush  configuration of the floor.
> 
> Of the products out there cement boards  I would opt to work with Hardi Backer board every time . It is much easier to work with, easier to cut.
> '
> ...



Could you say more about Hardi Backer board's workability & strength characteristics?  I want to put a noncombustible surface on the underside of a ceiling, and want something that won't sag, etc.  So far it seemed Durock was the stiffest/strongest choice.


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## CHIMENEA (Jan 3, 2011)

java said:
			
		

> Micore 300:
> 
> 
> Mantels Direct - http://www.mantelsdirect.com/s.nl/it.A/id.52283/.f?sc=18&category=304




I ordered Micore for my hearth from there. Arrived in good shape via ups free shipping.


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## michaeldd (Jan 3, 2011)

BeGreen,

Apologies if this thread isn't appropriate.  I wasn't sure where to post so I decided to post in a thread from which I gathered information and in which the Defiant, Micore, and hearths were topics of discussion.

Re the curtain, clearances, etc., the photo which shows the curtain was taken immediately after the stove was placed.  More work was accomplished afterward as can be seen in a different photo.  

I search all over the 'net using as many variations of Installation and Planning Guide as I could think of without success, then tonight I picked up a copy of a Defiant user's manual which I had misplaced and lo and behold, there it was, stapled to the back!  Anyway, clearances from the corners to the wall (not the Durock shielding) is 18 inches; the stove has a rear heat shield.

Yeah, I could probably lose the square footing bricks, but now they're mortared and grouted in place, and I don't feel like moving the stove at all to remove the aluminum until summer when I'll rebuild the stove.  One of the reasons I wanted to share that particular item is because I hadn't seen or read about such a thing and wanted to share it with the community.  Perhaps it could be useful to someone.


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## GlennMike (Jan 3, 2011)

Does anybody know what those 2' x 4' standard ceiling tiles that you see everywhere are made out of???  I just finished my install a little bit ago, used micore, but when I was browsing at home cheapo I took a good hard look at em and it looked very similiar to micore???  for like $2 a pop


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## begreen (Jan 3, 2011)

michaeldd said:
			
		

> BeGreen,
> 
> Apologies if this thread isn't appropriate.  I wasn't sure where to post so I decided to post in a thread from which I gathered information and in which the Defiant, Micore, and hearths were topics of discussion.
> 
> ...



Hey Michael, no problem. I found your planning somewhat unique and thought it deserved it's own thread for posterity and easier searching. You deserve good feedback for doing the research and photo documentation. Thanks for posting these good details. 

If you can scan the VC installation guide and send it to me via a PM, I will add it to the wiki docs.


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## michaeldd (Jan 3, 2011)

Gotcha.  I'll new thread it soon with pics.


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