RE: Questions about subfloor for hearth

[firefighterjake]

I'm hoping to tackle my hearth this weekend. Basically I only need ember protection, but I'm going to put down at least one 1/2 sheet of Durock and then do tiles on top of this.

Right now I have 1/2 to 3/4 inch of plywood and then 3/4 inch particle board followed by the padding and carpeting. My thinking was to remove the pad and carpeting. Screw the Durock into the underlayment with a boat-load of screws and use latex-added thinset for the tiles.

Questions:

1) Should I remove the particle board and replace it with plywood or is this a non-issue? One fellow that I spoke with said he thought I should remove the particle board in case moisture gets to it, causing it to swell and crack the tiles . . . but then again he also admitted that he has always laid tile directly to plywood and has only used cement board when working in bathrooms.

2) Is there a better way of securing the Durock or is screwing it down to the subfloor OK?

3) Is there anything else I should be doing . . . or doing differently?

As always, thank you for your advice.

 

[fossil]

Spread a layer of thinset with your tile-setting trowel onto the particle board, lay the durock and screw it down. Rick

 

[ScottF]

As a contractor I would never leave particle board underneath. It moves and swells with the least bit of moisture change. It will move the durock and crack the tile. No good wood floor contractor would ever leave particle board down either under wood floors for the same reason. Believe me remove the fall a particle board. Its a disaster waiting to happen. It will be well worth the time. I have seen many times tiles pop and crack because of particle board below.

Also FYI, never thinset tile directly to plywood. I have seen a million time. The floor gets water. plywood swells and pops tile. Durock is the buffer between that allows wood to move.

 

[ScottF]

also screwing the durock to the sub floor is good. Try to go every 6 inches square for a great job.

 

[fossil]

Scott's advice is unquestionably the best way to do it. If you're willing to go the extra step to remove the particle board and replace it with a like-thickness sheet of plywood, then thinset & screw the durock down, then set your tile atop the durock. I'm not a pro, but I've done a heck of a lot of DIY tile installations on floors, walls, and countertops. I've never set floor or countertop tile directly on anything other than durock. Rick

 

[ScottF]

Good point fossil. I forgot about setting the durock in thinset. That is definately the way to do it.

We had a friend who set $8000 worth of marble in thinset over a plywood floor in a bathroom. Toilet overflowed , Moisture got to all the plywood and popped all of the marble. No longer any good because you cant get the thinset off the marble. Durock would have prevented this. We saved it by setting each piece back down individually with boat building epoxy. Left the thinset right in place.

Particle board swells if you breath on it too hard.

 

[fossil]

Yeah, in a wet location it's a disaster waiting to happen. Beneath a woodstove, I wouldn't be quite as concerned about it, but removing the particle board removes all doubt. Rick

 

[begreen]

I still wouldn't put a wet material - thinset, on particle board as it will likely swell from the moisture. Add a layer of plywood on top of the particle board or skip the first thinset layer. With the durock screwed every 8" with the proper screws, it is not going anywhere.

 

[firefighterjake]

Based on the feedback here and bandying about ideas for a hearth with my wife I have modified my plans.

Now I'm working on building a "portable" hearthpad . . . although "portable" might not be most accurate word since I've only put the plywood base together (two 1/2 inch pieces of plywood screwed and nailed every 6 inches) and the corner install dimensions are something like 56 x 56 x 38 x 24 (or something close to these figures) and this thing already weighs a ton.

I'm picking up the Durock today (HD in Waterville doesn't carry Durock for some reason whereas the Bangor HD does) and will be using Flexbond thinset to "stick" the Durock (along with screws) to the plywood sheets. After the Durock sets up I hope to lay out some slate tiles (gauged 1/4 inch) that I was given several years ago) and use the Flexbond to set them in place before grouting and then sealing up the slate and adding the wood trim to the outside of the "portable" hearthpad.

Thanks again for everyone's advice.

 

[fossil]

I hope you're building it where it's gonna sit, because it sounds about as "portable" as the stove you're going to set on top of it. Rick

 

[HearthKB]

Based on the feedback here and bandying about ideas for a hearth with my wife I have modified my plans.

Now I'm working on building a "portable" hearthpad . . . although "portable" might not be most accurate word since I've only put the plywood base together (two 1/2 inch pieces of plywood screwed and nailed every 6 inches) and the corner install dimensions are something like 56 x 56 x 38 x 24 (or something close to these figures) and this thing already weighs a ton.

I'm picking up the Durock today (HD in Waterville doesn't carry Durock for some reason whereas the Bangor HD does) and will be using Flexbond thinset to "stick" the Durock (along with screws) to the plywood sheets. After the Durock sets up I hope to lay out some slate tiles (gauged 1/4 inch) that I was given several years ago) and use the Flexbond to set them in place before grouting and then sealing up the slate and adding the wood trim to the outside of the "portable" hearthpad.

Thanks again for everyone's advice.

I just ordered a Woodstock Fireview and plan on building my own hearth as well. On the Woodstock website it says to use 3/4" plywood, 1/2" Durock then tile on top. It didn't mention that I should use 1" plywood like you did, nor did it mention using thinset between the durock to the plywood.

So... Is it ok to just go by what the Woodstock website says, or should I use 1" plywood and thinset between the plywood and Durock?

 

[begreen]

You can get 5/4 plywood which is nice and rigid. That's what we used as underlayment for our tile floors.

 

[fossil]

Yes, you should thinset and screw the Durock to the underlayment. Rick

 

[firefighterjake]

I hope you're building it where it's gonna sit, because it sounds about as "portable" as the stove you're going to set on top of it. Rick

Well I've built the plywood base in the garage . . . but very soon (after cutting and fitting the Durock and side trim) I will be moving the wooden base into its new home since I think moving this monstrosity will be quite the challenge if I put the Durock on to it.

 

[firefighterjake]

Based on the feedback here and bandying about ideas for a hearth with my wife I have modified my plans.

Now I'm working on building a "portable" hearthpad . . . although "portable" might not be most accurate word since I've only put the plywood base together (two 1/2 inch pieces of plywood screwed and nailed every 6 inches) and the corner install dimensions are something like 56 x 56 x 38 x 24 (or something close to these figures) and this thing already weighs a ton.

I'm picking up the Durock today (HD in Waterville doesn't carry Durock for some reason whereas the Bangor HD does) and will be using Flexbond thinset to "stick" the Durock (along with screws) to the plywood sheets. After the Durock sets up I hope to lay out some slate tiles (gauged 1/4 inch) that I was given several years ago) and use the Flexbond to set them in place before grouting and then sealing up the slate and adding the wood trim to the outside of the "portable" hearthpad.

Thanks again for everyone's advice.

I just ordered a Woodstock Fireview and plan on building my own hearth as well. On the Woodstock website it says to use 3/4" plywood, 1/2" Durock then tile on top. It didn't mention that I should use 1" plywood like you did, nor did it mention using thinset between the durock to the plywood.

So... Is it ok to just go by what the Woodstock website says, or should I use 1" plywood and thinset between the plywood and Durock?

It sounds like the Woodstock Fireview is a lot like the Jotul . . . I pretty much only needed ember protection, but figured if I was going to make a hearth then I would add in the 1/2 inch of Durock for the R-rating (figured it couldn't hurt things and with me peace of mind is a good thing) and to give me something to "tile" to vs. applying the tile directly to plywood.

The reason I went with two 1/2 sheets of plywood is due to the fact that a few folks said they would recommend having at least 1 1/4 inch base to avoid potential flex. While I could have gone with a 3/4 inch sheet of plywood and the 1/2 inch of Durock I opted to go with two 1/2 inch sheets since a) the size of my base would require at least two plywood sheets (and I figured it would be a stronger base if I tied the two pieces in with a second plywood sheet on top), b) I already had one 1/2 inch sheet of plywood kicking around so it was cheaper to buy a second 1/2 inch sheet vs. buying a 3/4 inch sheet of plywood and c) I figured the extra 1/4 inch can't hurt things in terms of flex.

The reason I will be using thinset between the plywood and Durock is that it seems to be the suggested practice based on what I've gleaned here by looking at the various threads.

 

[fossil]

I hope you're building it where it's gonna sit, because it sounds about as "portable" as the stove you're going to set on top of it. Rick

Well I've built the plywood base in the garage . . . but very soon (after cutting and fitting the Durock and side trim) I will be moving the wooden base into its new home since I think moving this monstrosity will be quite the challenge if I put the Durock on to it.

Good idea, Jake, because if you finish it in the garage, that's where it's gonna stay, and NFPA 211 says you can't have a woodstove in the garage. :lol: Rick

 

[ScottF]

Putting the thinset between the ply and durock isnt absolutely neccessary but it does make a much better job because it fills all the potential voids and thus eliminates any flex that could crack the tile. It is a good idea.