2.0 R Factor Hearth Pad for 13 NC

[BamaRama]

Having a problem finding the correct way to put a hearth pad together. I'm trying to keep it simple as possible and still have a pad that won't crack. I have found a lot of opinions, ideas, and methods, stack-ups etc, but none on the way I want to do it. The pad is going on to 3/4 sheathing with 16" OC joists and i want to cover with porcelain tile.

I want to make it 48x48. I have two 5/8" Micore 300 pads of this size, so I have my R factor.

How do I stack it up to reduce the risk of cracking tiles? I worry about the Micore compressing under the stove.

From the info I've found, I think I need to go with Micore and 1/2 Durock screwed to floor, then Micore and 1/2 Durock screwed to the 1st layer of Durock, then modified thin set and tile.

The only Durock I can get is 1/2" 3x5'.

And it stands to reason that leaving the pedestal on the stove (rather than installing the legs) will reduce the risk of cracking tiles.

Any input is greatly appreciated.

 

[Jags]

I happen to know for a fact that durock is manufactured in 4 x 8 sheets as well. Not sure about your availability but you might want to check a real drywall yard instead of the home improvement stores.

 

[BamaRama]

I saw the 4x8 on the spec sheet. Building supply said he had never seen any. Do you think solid sheets of Durock would be better than orienting the seams of the layers 90* apart?

 

[Jags]

There is no problem with seams as long as they meet on a 2 x.(4,6,8), but as I understand, this is not how your build will go. I would look for a solid sheet if possible.

 

[BamaRama]

Other than avoiding the seams, any other suggestions? I was considering starting with 3/4 plywood so the screws can get more bite. I have a tendency to make stuff bomb proof.

 

[BamaRama]

I found the solid sheets about an hour away... 1/2 and 5/8... thanks for the suggestion.

 

[TheRambler]

Definitely go with 3/4 ply as the base, then 2 layers of micore with durock on top screwed down to the ply. Should have no issues with cracking. If your real concerned you can use grout and thinset with a bottle of the latex additive stuff to give it more flex/ crack resistance.

 

[BamaRama]

then 2 layers of micore with durock on top screwed down to the ply.

Would layering the Micore be better than sandwiching Durock between? My thought is the layering would help alleviate the compression with the Durock taking any load transferred through the first layer of Micore. Just trying to learn here.

And using your suggestion, do you propose dry stacking and using screws with mortar only under the tiles?

 

[Poindexter]

My stack is in a corner of walls with a chunk of angle iron across the front to keep the stack from sliding.

I put the floor part under the carpet by taking the pad out from underneath, rather than trying to cut a groove in the micore.

 

[TheRambler]

Alternating micore and durock wont hurt but i doubt it will help either. If you have a 3/4 plywood base and everything screwed securely then it will be fine. You only need thinset under the tiles.

There are alot of ways to accomplish the end goal, but they all achieve the same end result IMO. I would go withwhatever method you are most comfortable with.

 

[Jags]

No need to alternate the stack. No reason to thin set between durock sheets.

 

[BamaRama]

I initially miscalculated my materials. I have 3/4 Micore (R1.53) and 5/8 Durock (R.49) going on a plywood base so I only need three slices for my sandwich. I was about to install a 4.04 r factor heart pad.

Life is good