Thinset under hardwood

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  #1  
Old 07-05-15, 11:50 AM
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Thinset under hardwood

I'm planning to tile a hearth in front of my fire place. The rest of the flooring in the room is 3/4" oak hardwood. In the pictures, you can see that around the hearth, there is a border of hardwood. The board closest to the hearth has nothing underneath it. Before we removed the old hearth tile, there was some old concrete/thinset under the wood bordering the hearth.

Before I install the new tile, I want to get something under the hardwood so it's supported. The board is about an inch wide, and there is about an inch between the board and the concrete below it. Could I just pack this gap with some thinset?

Or would I be better off cutting a 1/2 or 3/4 piece of wood as a shim, and then packing some thinset or concrete underneath the shim?

Hope this makes sense.

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  #2  
Old 07-05-15, 12:08 PM
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Depending on how deep the space is I would use 3/4 or 5/4" wood as a support under the hardwood. I don't think filling the space with thinset is such a bad idea, but you need to let it cure before you put pressure on it. Either way, you definitely need support there.

I looked again, and you are on a concrete substrate, so the thinset may work best. Hang in there as our other pros will check in and offer good advice as well.
 
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Old 07-05-15, 01:30 PM
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Got a royal mess there.
Hardwood laid over a concrete rough slab?
 
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Old 07-05-15, 01:31 PM
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Before I install the new tile
Are you planning on building up the area in advance of the tile? or are you going to tile direct to the concrete? Seems to me that you would want the hearth to stand proud of the level of the wood or at least flush. Therefore you must build it up with something. Give us a little more detail of your plan and we can tweak as needed.
 
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Old 07-05-15, 01:57 PM
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Yeah, let me clarify. The only portion of the hardwood floor that is over concrete is the single board surrounding the hearth, where the hearth meets the hardwood. The rest of the floor in the room is a typical old house set up: hardwood is nailed to wood subfloor, which is nailed to joists. There is a basement below the room.

The hearth has wood somewhere below it, but that concrete you see is a couple inches thick.

My plan was to build up on top of the existing concrete. I was planning for tile to be flush with the surrounding hardwood, or slightly above. So I was going to smooth out the concrete, then build up with plywood.

Before I do that, I want to get something underneath the border hardwood for support.
 
  #6  
Old 07-05-15, 02:21 PM
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So I was going to smooth out the concrete, then build up with plywood.
That is why I asked, you can not tile direct to plywood, you need a buffer like cement backer. But it doesn't make sense to put cement backer on cement. I would use a self leveling compound to raise the whole slab to your desired height and then tile on top of that. Keep in mind that you need to use a self leveling primer before application of the self leveling compound or you will have adhesion issues. The self leveling will also take care of your crumbled area under the wood border.

Read the instructions on the self leveling compound and make sure the brand is capable of a pour as thick as you need it to be. Some varieties can only be poured to 1/2" in a single session, others to almost 1".

Tape off the edge of your hardwood to protect it and mask the rest of the room. The primer takes about 2 hours to set up and you have to pour withing a window of setting up or you have to start over. Have a trowel handy so you can assist the compound to level out - don't just pour and walk away, it needs to be massaged. Works great if you have dowels or metal bars of the correct pour thickness that you can put down as a screed to gauge depth of the pour. And lastly, you may need to isolate the SLC from the hardwood to keep it from touching. If you pour it tight up to the hardwood it may impact the ability of the wood to expand and contract with the seasons.
 
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