Install self leveling concrete ontop of backerboard then install tile?

benshouse

Hi,

I have a wood subfloor and I laid down backerboard last night. Today, I notice that the one piece is a little higher then other piece. There is maybe less then 1/8". My floor wasnt that level to begin with either. The backerboard feels solid so i dont think i have a problem with voids. Can i level with the thinset while installing tiles or will that create a bigger issue with the tile?

The directions said not to put the self leveler on the wood subfloor without metal/plastic lathe. I thought i might get it level with the thinset and backerboard, which it seems better but its not perfect. Can I now do the self leveler on the backerboard?

my tiles are 3"x6" marble

thanks,

ben

firehawkmph

Ben,
I don't think I would use floor leveling compound on top of the cement board. If it is just one seam, why don't you try and grind that piece where it is sticking up. If it's less than 1/8" it shouldn't take much. If you don't have any ridges sticking up, you should be able to get the tiles to lay flat. Use a 1/4" notched trowel and watch how you set them. That should provide you with enough adjustment.
The other thing Ben, how big an area are you tiling? Is the rest of the floor flat or do you have a number of dips? If the area isn't that large, you could take a 4' straight edge (level works) and find your high spots. You could mix up some thinsets and use it to fill in the low areas, checking with the straight edge as you go. If it's an old level, use it like a screed and pretend you are doing concrete. Let it dry overnight, scrape of any ridges sticking up and start your tile.
Mike Hawkins

tpolk

what hawk said

benshouse

Thanks mike...

The area is a small half bath (4ft x 3ft). Oh so you can put the thinset on a dried layer of thin set? Cool.

I am going to do a dry run later tonight and set up my lines and where i need to make cuts. So i guess i will see how much lippage (if that is a word?) i actually have in that area.

firehawkmph

Ben,
If the room is that small, I wouldn't worry about the slight mismatch. Put a piece of the nylon tape made for cement board on it and level the whole section with thinset like I said before. Should be pretty simple.
Mike Hawkins

Earthmaster

You could also step up to a medium bed mortar which will allow you to float that area rather than just try to level it. As you are using marble anyway it would be a better choice and you could use a 1/4x3/8 nothch trowel that should put enough mortar down for you.

hopefully you did put mortar under the backerboard and tape the joints.

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sourek

I do tile for a living.. Hope there is thinset under the board, tape seams. If the seam isn't that high like you said, just grind it and retape and mud it. The 1/4 by 3/8 will give you more adjustment of the tile. Make sure you have at least 90% coverage on back of tile if its stone. You don't need a lathe for Custom Building Products self-leveler sold at homedepot. Just a primer. Some levelers do require it though. Custom Building Products says no to the self leveler on top of the cement board. Next time you should level the floor before putting down the cement board. Hope this helps, Tony