Stone slab hearth on wide plank floor

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slab

New Member
Sep 11, 2022
3
Greenland, NH
Hi,

I'm new here and have a question that I haven't found a clear answer for after scouring the forum. I'm trying to install a wood stove (Pleasant hearth 1800) in my living room. The house is old (1860s) and the living room has wide plank floors-- no sub flooring, just joists. I would like to get a soapstone or granite slab to serve as a hearth pad with the stove sitting on top.

I am not sure how to attach the slab to the floor. Do I need a membrane like ditra to allow the slab to expand/contract with heat separately from the floor? Additionally it's an old house and the boards aren't totally level-- what should I use to level the hearth slab?

Thanks! Any ideas are appreciated.
 

begreen

Mooderator
Staff member
Nov 18, 2005
96,422
South Puget Sound, WA
Start with the insulation requirements for the stove first. According to the manual:
The floor protector must be a durable noncombustible material with a minimum thickness of 0.5” and an R value of “1.06”.
A slab of stone will need an insulator underneath it to meet this requirement.
 
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slab

New Member
Sep 11, 2022
3
Greenland, NH
Good point. I could put down a 1/2 inch micore fiber board underneath which should get me an R value of 1.47.

Any recommendations as to how to attach the fiber board to the floor and to the slab?
 

begreen

Mooderator
Staff member
Nov 18, 2005
96,422
South Puget Sound, WA
It would be passive and just sit there. Micore is too fibrous to attach to. It would need a layer of cement board on top. That sandwich could be screwed down. Or two layers of 1/2" Durock NexGen (the lighter-weight concrete board) would get the R value close. This can be screwed down per mfg directions, then the slab can be set with a coat of latex-modified thinset on the cement board.
 

71montess

New Member
Mar 27, 2021
65
Base camp
If the stove manual says ember protection is only needed, the correct size slab of stone on the floor is all that’s needed. No need to adhere it to floor either.
 
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EbS-P

Minister of Fire
Jan 19, 2019
3,553
SE North Carolina
Are you planning a single piece of stone or tiling stones?
 

begreen

Mooderator
Staff member
Nov 18, 2005
96,422
South Puget Sound, WA
If the stove manual says ember protection is only needed, the correct size slab of stone on the floor is all that’s needed. No need to adhere it to floor either.
That is not the case here.
 

Ashful

Minister of Fire
Mar 7, 2012
17,633
Philadelphia
Wouldn't gravity and a 600 lb. stove atop the slab be sufficient to hold it in place? I'd not be too anxious to put even more holes in an already old floor.
 

begreen

Mooderator
Staff member
Nov 18, 2005
96,422
South Puget Sound, WA
Wouldn't gravity and a 600 lb. stove atop the slab be sufficient to hold it in place? I'd not be too anxious to put even more holes in an already old floor.
Yes, but it will need an insulation layer in order to meet the hearth requirement.
 
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