Typical requirements for a hearth pad

[dnichols822]

Hello,

I need to replace my tile under my woodstove and in doing so I noticed there is plywood underneath it that is scorched. So I wanted to redo it right. Does anyone know how to make it safe? I've heard Durock but how thick and how many sheets should I use?

 

[begreen]

Yikes! Good you discovered this. Hearth requirements vary from stove to stove. What's the stove make and model?

 

[dnichols822]

My make and model is .... Bullard FSA-104 Falcon . I can't find any information on this woodstove online and I have no manuals to look at. And for the record I still don't know for sure what to use to bond the porcelain tiles to the cement board underneath the woodstove. I tried a tile forum and got 3 different answers.

 

[dnichols822]

I found the following thin set that is sold at home depot by me. Is this ok?

FlexBond Fortified Thin-Set Mortar is a polymer-modified, premium mortar offering exceptional flexibility and bond strength. Protects against tile cracking from minor surface movement. Can tile directly over cracks up to 1/16 In. without repairs. Exceeds ANSI A118.4, A118.11 specifications. Polymer-modified for strength, just add water and mix, no additives required. Eligible for a lifetime warranty.

* Polymer-modified, premium flexible mortar
* Exceptional bond strength and flexibility
* Outstanding bond to wood floors, glass and porcelain tile
* Protects against tile cracks up to 1/16”

 

[Elfin]

Flexbond is a very good product. HD also sells Versabond, which would also work just fine (and it's lots cheaper).

 

[begreen]

Ok, I can't find anything either. Can you post a picture of this stove?

It obviously is radiating a lot of heat downward. That makes it hard to give you useful info about how to rebuild the hearth. Adding a layer of Durock may be insufficient insulation. The last thing you want is to rebuild a time bomb that is still cooking under the stove. As a possible solution, I am thinking of adding a heat shield to the stove as well as building up the hearth.

 

[fossil]

Yeah, latex modified thinset's what you want to use to set the tiles on the tile substrate (presumably Durock)...but before you start thinking about that, you need to start thinking about constructing a hearth that has some insulative value between the stove and the nearest combustible material. If you know nothing about the stove, and can't find out anything about the stove, then I suggest you be very conservative (go overboard) on the R-value of the hearth you put beneath that thing, lest one day your subflooring begin to smolder. Rick

EDIT: If you can find nothing about your stove, you need to default to the requirements of NFPA 211 Section 12.5, and then how you construct the hearth depends on the clearance between the bottom of the stove and the floor. A bottom heat shield for the stove would certainly be a good idea, too. We really need to see a pic of the stove.

 

[Brian VT]

Sorry to cut in, but it's on topic and my searches didn't find an answer.
I have my VC Resolute Acclaim 2490 temporarily on one of those black Imperial stove boards which is on vinyl(?) flooring which is on a concrete basement slab floor.
It's "rugged" vinyl like what might be used in an institutional setting. Not the thin stuff like those square tiles in a box.
I downloaded the stove's manual and it doesn't give very specific info for bottom clearance/etc. other than saying "most installations require the use of the bottom heat shield" which I don't have. Am I okay or can heat through the board cause an issue with the flooring ?
I'll make a nice hearth base if this setup works for us but it's an experiment for this winter so I don't want to get too involved except for safety concerns.

 

[begreen]

Get the bottom heat shield for the stove Brian and you'll be ok. From the manual:

"Most installations will require that the bottom heat
shield be attached. Only when the stove is placed on a
completely noncombustible surface such as unpainted
concrete over earth may it be used without the heat
shield."

 

[dnichols822]

I have posted a picture of it in a different thread. The link to it is below. The stove is almost 6 inches off the ground.

https://www.hearth.com/econtent/index.php?ACT=24&fid=2&aid=13118_SmZli58DuwUPYAktT1NJ&board_id=1

By the way, I am building a heat shield on the back wall...

 

[Brian VT]

Get the bottom heat shield for the stove Brian...

Will do. Thanks.
If this works out I hope to make a nice hearth and set an Alderlea there. :cheese:

 

[begreen]

D-nic, that helps. Short legs, no ash pan. This stove must get pretty hot in the belly. The safest thing I can suggest is to put a layer of bricks or 4" cement half-blocks on the existing hearth and then a layer of sheetmetal on top of the bricks.

 

[fossil]

Oh yeah, I remember this installation now. So, that raised hearth was originally built up with wood except for a tile surface on top? Not good. You need to rip out that whole hearth and start from the floor up with non-combustibles. Maybe 4 layers of 1/2" durock, with a sheet of 24 gauge steel sandwiched in, and then put your new tile on top...something like that. Then you can sleep at night (and wake up in the morning!). Rick

 

[dnichols822]

Yes, the wood stove was completely out of code. The back of the wood stove says the hearth needs to extend 18 inches and the heart only extends 13 and then the tiles are placed directly over plywood. I wanted to avoid tearing up the hearth if possible to save time.

 

[dnichols822]

D-nic, that helps. Short legs, no ash pan. This stove must get pretty hot in the belly. The safest thing I can suggest is to put a layer of bricks or 4" cement half-blocks on the existing hearth and then a layer of sheetmetal on top of the bricks.

Umm, what? A layer of bricks? I have no idea how to do this? How about if I put several pieces of durock? What does the sheet metal do? Help disperse the heat?

 

[begreen]

A layer of bricks means just that. You would need enough bricks to create a solid bed of bricks under the stove. The sheet metal will serve to reflect and diffuse the heat before it reaches the bricks. Durock might work, or it might not. The objective is to remove speculation.

 

[fossil]

Bricks, Durock, it doesn't matter...it's all non-combustible "masonry". What does matter is that the installation be done safely. Just stuffing masonry into the 6" space beneath the stove is not the appropriate solution. The stove sits ~6" above whatever it's resting on, and what it's resting on should then provide an additional significant insulative value between the stove and the combustible floor beneath. In the case of an unlisted stove that sits with not less than 6" of ventilated space beneath the bottom of the firebox, NFPA 211 calls for 2" of masonry topped with 24 gauge sheet metal, extending not less than 18" beyond the stove on all sides. There are a lot of ways to meet or exceed that requirement in a pleasing way. There are a lot of very displeasing ways of failing to meet that requirement. Rick

 

[dnichols822]

Ok, so I put the sheet metal on top of 4 layers of 1/2 inch Durock? Can I put it under a layer so I can lay the tiles on top of Durock? How do I bind the sheet metal to the durock...good ole thin set again?

Thank you all for you help in getting my hearth and home safer!