Hearth Pad Plan

[Tahoe]

Hi Everyone,

Thanks for your help so far in selecting a stove, chimney, etc. I've decided on the Progress Hybrid from Woodstock. The chimney will be exposed double wall black stovepipe extending to the ceiling/roof, and on up from there to meet clearance requirements. The chimney sweep came out today to scope it out and will do the stove/chimney installation. Now, I've just got to make a nice looking hearth pad.

Here's the plan for the hearth pad:

• Bottom layer: 3/4” plywood, R value 0.94
• 2nd Layer: ½” micore 300, R value 1.04
• 3rd Layer: ½” plywood, R value 0.63
• Layer of Thinset, 1/8”
• 4th Layer: 0.42” Hardibacker cement board, R value 0.2 (using this instead of durock out of concerns that the new lighter durock has something meltable in it and/or could break down when exposed to heat)
• Layer of Thinset, 1/8”
• Layer of tile, ¼”

Total Thickness: 2.42”
Total R value: 2.48
Required R value for Woodstock Progress Hybrid: 0.8
All front/back/side clearances will be appropriate per manufacturer recs.

Does this seem reasonable? Is there anything I'm forgetting about?

Thanks for your help!
- Adam

 

[jetsam]

Hi Everyone,

Thanks for your help so far in selecting a stove, chimney, etc. I've decided on the Progress Hybrid from Woodstock. The chimney will be exposed double wall black stovepipe extending to the ceiling/roof, and on up from there to meet clearance requirements. The chimney sweep came out today to scope it out and will do the stove/chimney installation. Now, I've just got to make a nice looking hearth pad.

Here's the plan for the hearth pad:

• Bottom layer: 3/4” plywood, R value 0.94
• 2nd Layer: ½” micore 300, R value 1.04
• 3rd Layer: ½” plywood, R value 0.63
• Layer of Thinset, 1/8”
• 4th Layer: 0.42” Hardibacker cement board, R value 0.2 (using this instead of durock out of concerns that the new lighter durock has something meltable in it and/or could break down when exposed to heat)
• Layer of Thinset, 1/8”
• Layer of tile, ¼”

Total Thickness: 2.42”
Total R value: 2.48
Required R value for Woodstock Progress Hybrid: 0.8
All front/back/side clearances will be appropriate per manufacturer recs.

Does this seem reasonable? Is there anything I'm forgetting about?

Thanks for your help!
- Adam

You only have R0.2 between the stove and combustibles. The plywood is combustible.

Move the micore up to the top, right under the hardieboard. You can ditch the plywood unless you just need the height.

 

[Tahoe]

You only have R0.2 between the stove and combustibles. The plywood is combustible.

Move the micore up to the top, right under the hardieboard. You can ditch the plywood unless you just need the height.

Crap, good call. Will thinset stick to microcore? I'm also worried that it'll be squishy and allow for movement in the tile/grout. Maybe two layers of hardieboard with microcore sandwiched between?

Thanks... glad I asked!

 

[begreen]

No micore is too porous. The proper way to build this is with the plywood base, then micore, then cement board then tile. Durock NexGen has pumice in it. Hardibacker has a cellulose filler.

 

[jetsam]

Crap, good call. Will thinset stick to microcore? I'm also worried that it'll be squishy and allow for movement in the tile/grout. Maybe two layers of hardieboard with microcore sandwiched between?

Thanks... glad I asked!

Like I said, micore goes right under the hardieboard. Use a polymer modified thinset if you're worried about flex. You can put plywood underneath, but if it's going on a nice flat wood subfloor, I don't think it matters. If it's going on top of wood flooring, yes plywood because the flooring is possibly not real flat, and its flatness can change more over time even if you level it.

I don't have a strong opinion on durock vs hardieboard. I've torched both with mapp gas and they both put up with it fine. Hardie has cellulose in it and durock has fiberglass ends now. Hardieboard is tidier to work with, durock is cheaper. Both want special fasteners.

 

[Tahoe]

Thanks guys for your help! Seems like cellulose would be a bad idea. I’ll stick with the durockmost folks use. I may end up leaving the micore out entirely. I talked to Woodstock and they said it was a bit overkill.

 

[begreen]

Thanks guys for your help! Seems like cellulose would be a bad idea. I’ll stick with the durockmost folks use. I may end up leaving the micore out entirely. I talked to Woodstock and they said it was a bit overkill.

If a double layer of 1/2" Durock NexGen was used then the hearth would be close to the required insulation value.

 

[jetsam]

Thanks guys for your help! Seems like cellulose would be a bad idea. I’ll stick with the durockmost folks use. I may end up leaving the micore out entirely. I talked to Woodstock and they said it was a bit overkill.

Something that you can run a mapp gas torch on is not going to catch fire when it gets a coal on it. hardiebacker is cement and non combustible.

(broken link removed to https://www.jameshardie.com/product-support/resource-center/technical-documents/fire-prevention-faq?loc=refresh)

Hardiebacker, durock, and wonderboard are all fine for this application.

 

[begreen]

Hardiebacker, durock, and wonderboard are all fine for this application.

If you can find the original Wonderboard it's ok, but Wonderboard lite has styrofoam pellets in it. Do not use this.