Need help with my hearthpad :plywood and durock leveling

[prtp3warrior]

So I am building a hearths for a woodstove .

I have the location and clearances all figured out.

Under the stove I need .5 r. I chose two layers of durock on a plywood pad. That gives me .78 r so I am good.

The problem is that the plywood underlayment is not exactly level. There is about 1/4 inch of "play" between the edge of the plywood and the exsisting wood floor.

This means when you walk on the edge of the plywood it moves. I am afraid that once the durock and tiles are on, the thing will either flex and crack tiles when walked on or be wobbly.

Any suggestions?

 

[prtp3warrior]

Bumped because I changed the title and question. Hopefully I can get some help.

The last time I installed a stove this place was awesome.

 

[begreen]

That is going to depend on the source of uneveness and its nature. Do you know whether the floor surface is out of level or the plywood is slightly warped? If it is the floor is it cupped, off at just one end.? They make a self-leveling compound for uneven floors, but i've never used it.

 

[prtp3warrior]

I think that the plywood is slightly bowed.

 

[bholler]

Screwing the plywood down would be the easiest option

 

[begreen]

Yep. If you can put a straight-edge on the floor and it's level, just screw down the plywood to the floor.

 

[FTG-05]

Screw down, replace or delete the plywood. You know what you need to do Silver..... Don't paint over grease.




(broken image removed)

 

[Simonkenton]

Yes, I would locate the joists below, and get some 3 inch decking screws, and put screws `12 inches apart into every joist.

 

[prtp3warrior]

Screwing into the floor is Not an option. I do not want to tear up the wood floor. I went to home depot and all the plywood is a little bowed. Looks like I will be building a frame. Oh Well.

I wanted a raised hearth anyway. Wife wanted a lower profile.

Tried her way now I will do it my way.

Any advice on the proper thinset for the Durock?

 

[begreen]

If you want this to be free floating then it will need at least 3/4" plywood. They make 1 1/8" plywood if you want it extra flat. Two layers of Durock screwed down to the plywood should help stiffen it and flatten it out. Screw it once every 8". There's no need or benefit for thinset between the layers, just use the thinset for the tile. Latex modified thinset works well. The full pad assembly will be quite heavy. Have a couple helpers if you need to move it into place.

 

[Simonkenton]

You need to study up on proper installation of tile. If you don't screw that plywood into the joists, you are liable to wind up with cracked tiles.

 

[cableman]

Make a level frame as high as you want, fill with mud, (cement/sand mix). Maybe place some screening inside too.

 

[prtp3warrior]

Went ahead and built a frame.

Here is the frame.

(broken image removed)



And the Durock mortared down and taped.

(broken image removed)

This is my first experience with with mortar.

 

[jkranes]

I can't tell from the photo: did you put a sheet of plywood under the Durock?

 

[prtp3warrior]

Yes. 3/4 inch plywood base. It was the same piece that was slightly bowed. The frame totally fixed that issue. I will put one more piece of Durock down over the current one to give a r = .78 value. It will have the seems all offset by a good bit.

 

[begreen]

Looking good.

 

[prtp3warrior]

Ok so a bit of a snag. For my top layer of Durock, does it need to be screwed into the plywood or can it just be screwed into the base layer of Durock. I ask because it seems the screws going all the way into the plywood would allow heat to transfer into the plywood. I am planning to use thinset under the top layer.

 

[firefighterjake]

As long as you have tile or stone going over the top of the Durock I wouldn't worry too much about heat transfer myself.

That said . . . the goal is to mainly make sure the hearth will not move . . . unless it moves as an unit . . . to avoid causing any tile or stones to lift up.

 

[prtp3warrior]

Final layer of Duroc down.

(broken image removed)

 

[DougA]

The screws will not matter, just don't use a few thousand.

 

[begreen]

According to USG the Durock should be screwed down every 8". It should be thru-screwed to the plywood. Use proper cement board 1 5/8" screws. Don't worry about the heat transfer. It will be inconsequential in this application and diffused by the hearth tiles.

 

[fossil]

screws going all the way into the plywood would allow heat to transfer into the plywood.

This should not be a concern. Rick