Hearth pad help

[prestonmoler]

I am building my own hearth pad for a new woodstove. I have access to Micore 300 in 5/8th inch thickness (4x8 sheets). I am wondering if I build my frame and cover it with the micore then tile, or does it need plywood on the frame then micore, then tile? Also, would there be any reason to add a layer of sheet metal and if so, at what level in the pad? Will liquid nails hold tile to micore, or do I need to use thinset or some other adhesive?

Should I use cement board as the material directly below my tiles?

Does anyone know the R-Value of Micore 300 in 5/8th inch thickness? If I figured correct, it is 1.28.

How many layers of the Micore should I use so the pad could be used with any stove down the road?

Would 5/8th inch firerock be of use to me in this project?

I'm open to all ideas.

Thank you in advance for your input.

PJM

 

[begreen]

Craig has Micore 300 listed at R 2.33/inch. .625 x 2.33 = R 1.46.

What stove is this for? A lot of stoves don't have high R value hearth requirements so it is difficult to predict any stove down the road.

Micore itself is not structurally strong. It would not be a good tile underlayment. For a strong hearth you could have a layer of plywood, then the micore, then cement board (not fire rock), then the tile. Liquid nails is definitely not a good idea to use for tile setting, particularly not for a hearth.

Or if you want a completely non-combustible hearth it could be made using metal studs, 12" OC, with a steel skin attached to the tops, then the micore followed by 2 layers of 1/2" cement board. That would accommodate almost anything due to the increased R value created by the air space.

 

[fossil]

Yeah, what stove is it? And tell us more about what you call your "frame"...materials and configuration. And answer all the rest of BB's questions. And be quick about it. %-P Rick

 

[prestonmoler]

I have never worked with metal studs. Would an air space created by wood studs give the same effect. Hypothetical - 2x4 wood frame with 12 inch centers, 3/4 plywood, one layer of 5/8th micore 300, one layer 1/2 inch cement board, then tile. Would this be more than enough protection? I am down to the PE Summit, Quadr Fire 5700 Step Top, Quadra Fire Isle Royal as my top three.

 

[fossil]

Find the most restrictive R-value requirement from among your top three stoves and build to that, then you're covered for whichever one makes it to last stove standing. Rick

 

[prestonmoler]

I was looking at Quad manuals online. They give a required K value, I think it was .84 for the two Quads I mentioned. How do I change that to R value?

 

[fossil]

If you use combustible materials to create the airspace, then the R-value of the airspace doesn't count. The R-value must come from the combination of materials between the bottom of the appliance and the closest combustible material below. Rick

 

[prestonmoler]

Well using the wood materials covered as I described, will this be a good R value ie: Micore, cement board, tile

 

[Delta-T]

I was looking at Quad manuals online. They give a required K value, I think it was .84 for the two Quads I mentioned. How do I change that to R value?

k to R conversion:

R= 1/k x inches of thickness

 

[Delta-T]

my handy dandy Woodburning Hearth Systems Reference Manual (3rd edition) lists Micore 300 as R value of 2.18

 

[prestonmoler]

2.18 for what thickness sheet? The sheets available in my area are 5/8 in thick

 

[begreen]

I'm not sure where web got the R=2.33 from. But just to throw a monkey wrench in the calculations I went to USG's site and got the official R=2.06/inch for Micore 300.

So for 5/8" Micore 300 the R value is 1.29. Don't sweat it. You are ok with the hypothetical plan mentioned above. Go for it and use a decent thinset like Versabond for the tile bed.

 

[Delta-T]

ah, you gotta love "reference" material, LOL.
PJM- I think R values are always given "per inch thick"