Looking for hearth pad ideas.

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chris-mcpherson

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Jun 9, 2010
107
Virginia
Right now I have a slate pad in front of my gas logs that's too small for the new stove (HS Heritage) and will have to be replaced. This part of the stove/chimney install is my responsibility. I'm considering a prefab hearth pad but they seem needlessly expensive for what they are, though it would be just a matter of plunking one down on the floor (I'm assuming).
I haven't priced materials to build one myself yet but will be doing so in the next day or so. I'm guessing I build a frame, lay down some sort of backer board then tile...right? I'd love to just dry fit some flagstone.
If you've built one and have progress pics please show me what you did.

Simple and cheap are the goals for this part of the project!
 
You will have to get your hands on the install manual & see what the R-Value rating is for the floor protection under your stove.
Most people want to just use good ole stone. It IS fire proof, but it will transfer heat to the flooring below it, so it's NOT SAFE
in nominal thicknesses. To meet prescribed R-values, most stone needs to be 2, 3 even 4 inches thick OR MORE.
Your BEST bet is to read the manual, find the R-Value & get the materials that MEET that R-value.
Once you've gotten an approved design, THEN you can add whatever non-combustible finishing material you want.
I've said it before & I'll say it again. FIRE will do two things. It will HEAT your house, or it will EAT your house.
It doesn't care which & it doesn't care what you want. In fact it doesn't give a SH*T about you.
It just wants to consume whatever is there that is consumable.
As proof, fire departments save a LOT of basements EVERY Year...
Harsh? You bet. But them's the facts.
 
What stove Chris?
 
Ah, thanks I missed the HS Heritage. Needs an R 1.2 hearth. The rest is what he said. You can certainly build your own, but it needs to meet or exceed the stove spec.
 
That's right...the Heritage.

Update...my wife found a hearth pad that she likes enough to spend the money on. Less work for me and she gets to make a decision on this project... I win twice. I'll make sure the pad the she likes is suitable.
I really am appreciating the patients for my questions. There's nothing like being an informed consumer. Thanks guys.
 
Just a heads up, make sure the pad really is R=1.2

When I was checking these out for my project (VC Defiant 1910), the prefab pads tended to be R=1.1 to the thermonuclear version at R=3.

Will it make a difference missing the R=.1? Probably not. If you want that, an inch of common brick under the hearth pad gives you the R=.2, just make sure it's not grossly out of whack like R=.5
 
Back to the drawing board...the one she liked is discontinued. So...I'm back to building my own. Like I said originally, I'd like to keep it simple and cheap.
Thanks tiber and BeGreen for the R value info.
Do you think cement board and stone tile will do the trick? That's what all these prefab pads look like.
What about outdoor landscaping pavers?
I'll also do a search on this forum for ideas.
 
Thanks for the link.
BeGreen said:
Here is the Durock spec:

“Space-saving Durock® brand cement board is listed by Underwriters Laboratories, Inc., for use with UL-listed
solid-fuel room heaters and fireplace stoves. Used as a wall shield, Durock cement board reduces by two-thirds
the manufacturer-specified clearance (minimum 12”) between the room heater or stove and a combustible wall
surface. 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 ≤ 0.84 Btu in./(ft. ² h °F) in the minimum dimensions specified by the room
heater/stove manufacturer.)”
http://www.usg.com/USG_Marketing_Co...d_Submittal_Sheets/CB198_Durock_Cement_Bd.pdf

The R/K value specs are here on page 2:
http://www.usg.com/USG_Marketing_Co...ts/DrckCement_Board-Submittal_Sheet_CB399.pdf
1/2” Durock R= .26, K value = 1.92
Click to expand...

If I'm reading things right...it looks like I can use 5 layers of 1/2" Durock and achieve an R value of 1.3 plus whatever thin set and stone tile add (probably not much, if any).
Is that the type board you used? If not, what was and how many layers?
But...as it stands now, I'll do the 5 layers...finish with a tile of my choice and then edge with trim and be done with it.
 
I too used gypsum board, it's a good choice. I used one 5/8ths inch sheet with 3/8ths inch tile on top. VC Defiants (my stove) don't need an R requirement for the floor, but most stoves require at least R=.5 by my research which this meets (R=.56). Guess you picked a winner. ;) Tile gives you an R of 0.02 per quarter inch, so it's effectively useless for thermal resistence. I spent the extra $2 for "fire rated" gypsum since it's going to have burning material on top of it (hopefully always in the stove). You're doing The Right Thing by checking the manufacturers spec sheet, you're on the right track.

The thin set - just make sure it's some variety of the "high temp" stuff to put up with the expansion and contraction. Most "shower and sauna" stuff fits this category. You'll have popped tiles/stones if you cheap out. The same goes for the grout. I avoided latex modified grout simply because I didn't feel safe with it, so my grout was slow setting old school sandy stuff. I wish I hadn't tossed the tubs of grout and thin set or I'd post the brands. That tile was from lowes and the gypsum, grout and thinset was from home depot.

The surface requirement for noncombustable will be met if you're using stone or tile. If you're using cultured stone or river-rock, ask if you can use it in a firepit. Some of it is hollow and will explode, some of it is painted, river rocks can have pockets of water. If you go the tile route, ask the same question since some of it is little more than hard vinyl or rubber. If it says porcelain or glass it's entirely safe.
 
Instead of stacking 5 sheets of durock, why don't you use some metal studs on end and build a platform (maybe 12" on center?)? Cover the platform with a layer (or two) of 1/2" durock, plus thinset/tile. The air space along with the durock/tile cover will achieve your required R-value. The air gap alone will give you an R value of 1 (from quick r value chart i googled).
The hearth pad will end up being elevated a bit more than 5 sheets of durock, but will save you on overall material costs, and non-stove weight (the 3x5' sheets of durock are pretty heavy ~90lbs?) - 5 full sheets would be close to 500lbs, without the stove in place.

Dead-space air acts as a pretty good (and cheap) insulator!
 
They are 90lbs a pop. Trust me after moving that Defiant I can tell you picking up sheetrock is a cake walk.

I agree about the air with one caveat: The air has to flow under the hearth. The "dead air" arument I don't think holds water and that's why the "wall shields" portion of the code indicates that "at least 50% of 1 inch below and above the wall shields is open for air flow".
 
tiber said:
I too used gypsum board, it's a good choice. I used one 5/8ths inch sheet with 3/8ths inch tile on top. VC Defiants (my stove) don't need an R requirement for the floor, but most stoves require at least R=.5 by my research which this meets (R=.56).
Click to expand...

Did you mean R = .26? 1/2' cement board is R=.26
 
chris-mcpherson said:
Thanks for the link.
BeGreen said:
Here is the Durock spec:

The R/K value specs are here on page 2:
http://www.usg.com/USG_Marketing_Co...ts/DrckCement_Board-Submittal_Sheet_CB399.pdf
1/2” Durock R= .26, K value = 1.92
Click to expand...

If I'm reading things right...it looks like I can use 5 layers of 1/2" Durock and achieve an R value of 1.3 plus whatever thin set and stone tile add (probably not much, if any).
Is that the type board you used? If not, what was and how many layers?
But...as it stands now, I'll do the 5 layers...finish with a tile of my choice and then edge with trim and be done with it.
Click to expand...

That is one way to do it. Or you could use a sheet of Micore or similar insulation board under one sheet of Durock. Or you could use an air space with two sheets of cement board on top (double sheets to add rigidity) like VTHC suggested.
 
Hope not. That's wallboard!
 
BeGreen said:
Hope not. That's wallboard!
Click to expand...

It's not "wallboard" as in "plain vanilla gypsum covered in paper", he's doing the right thing in my opinion, and yes I used it.

Yeah, gold bond is the top of the line fire stuff (exceeds "type x"). However type X is a designation whereas Gold Bond is a brand which exceeds Type X spec. It's got little fibers in it which make it a real PITA to cut, have a drywall blade and a razor ready and cut whatever fibers bind up the drywall saw.

All about the fire standards and gypsum products:
http://www.nationalgypsum.com/resources/faqs/gypboard.aspx
http://www.nationalgypsum.com/resources/safetyinformation/

Keep in mind you still have to meet the surface requirement for nonflammable which gives you a nonflammable assembly for a given R value.

EDIT: Micore 300 has a staggering R=1.03 for a half inch. Per the spec sheet ( http://literature.usg.com/pdf/IW803.pdf ) it still has to be covered in noncombustable material.
 
Tiber stole my thunder.. I was looking into this a bit of time ago and I found that Micore 300 was the best bet.. Unforunately I have no idea where to find it. I found a place online, but shipping is a killer.


If anyone knows of a good place to find Micore 300, please let me know. (although I have a cement slab for a floor so I would only be interested for curiosities sake)
 
Bobforsaken said:
Tiber stole my thunder.. I was looking into this a bit of time ago and I found that Micore 300 was the best bet.. Unforunately I have no idea where to find it. I found a place online, but shipping is a killer.

If anyone knows of a good place to find Micore 300, please let me know. (although I have a cement slab for a floor so I would only be interested for curiosities sake)
Click to expand...

Home depot wanted $75 for a 4x4 sheet, special order. I went back to gold bond. :(
 
Okay...I feel like I'm narroing in on a solution.
I didn't realize the Durock is so heavy...I don't wanna add ~500 to the job.

I found this:
https://www.hearth.com/econtent/index.php/articles/k_values_what_does_it_all_mean

I think I found a local supplier for the Micore 300.

Once I remove the existing hearth pad that's too small I'm sure it will just be subfloor underneath.
By the looks of it, I can use two sheets of 1/2" Micore 300 or four sheets of 5/8" fire rated gypsum board on the subfloor then finish with tile/stone...correct?
 
It depends on the subfloor. If it's plywood it's probably thin stuff. If you know how thick it is, you can figure in the R value of the plywood: http://www.sizes.com/units/rvalue.htm If you don't know you might want to overbuild.

You need R=1.2, so one layer of half inch won't do it since half-inch micore 300 is R=1.03. Close, but it could be closer on the cheap.

If you put 5/8ths gold bond under it (or on it), you get R=0.56, and then 3/8ths inch tile fits nicely on top making the whole thing 1.5 inches thick with an R of 1.61 (tile is R=0.02).

You could put down plywood also - MORE PLYWOOD - half inch is R=.63 for a total of 1.68 - you get the idea...
 
Not sure why you're even referencing the R-value of plywood. Plywood is a combustible material. All of the required R-value of a non-combustible hearth is supposed to reside between the stove and the nearest combustible material. Plywood can certainly be beneath the hearth, but it most certainly cannot be factored in as a part of the hearth's R-value. Rick
 
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