Cement Backer Board on Cement Subfloor?

I'm planning on tiling the entryway around the cutout door to my basement (about 3' x 6') and a hearth in front of a fireplace. (about 2' x 4'). Both are going to be ceramic tile, and are going to be surrounded by wall to wall carpet on 3 sides. Right now, the floor is an unfinished cement floor, and the carpeters are coming in a week or two, so I need to get moving on the tile.
After talking to a guy at the store, we agree that I probably need a backerboard under the tiles, so that the height is proportionate to the surrounding carpet. (Moderately thick pile on top of a 3/8" moisture resistant pad). So I bought some 1/4" Durock cement backer boards, and was getting ready to start slicing them up and putting them down, when I thought of some more questions.
1) Do I need to (i) tape the seams and/or (ii) put down some moisture membrane on the area by the door, or can I just seal my grout and figure that it's cement all the way down?
2) How should I attach the backer board to a concrete subfloor? Will thinset be enough to hold it in place, or should I mess with masonry bits and screws, and if I need to screw it down, what kind of bit and screw should I use?
3) Is there a good way to figure out if I've got the tile at the right height? Would I be happier with 0" of backerboard (i.e. none), or 1/2"?
Thanks, TM
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I am not a tile pro just a DIY tile guy.
Thinset is not going to be enough to hold this stuff in place. And that is a lot of masonry screws.
You will need to float it of level if it has the tapered edges. Over concrete I doubt that tape is of any value.
My advice is to not bother. No one is going to really notice a half inch of difference. Your raw floor is stronger and more stable than what you are about to create.
Spend the money you are about to waste on some reason nice transition trim to cover the joint. The place to start looking would be where you are buying the carpet. A better deal may be available elsewhere but their installers may not want to install it if they don't get to sell it.
Colbyt
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scary snipped-for-privacy@hotmail.com wrote:

My primary trade is installing tile.
don't use durock, you want the tile to feel flat with carpet when it is being walked on, not just if it looks level.
use a sealer/blocker on concrete.
use premium adhesive/thinset/mortar it even mixes creamier than cheapo bag.
after grout cures (2 weeks +,-) use a 7 - 10 year sealer, this will keep the grout easy to clean and fresh looking for years.
Happy Installing
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Strictly speaking, you don't need backerboard, the tiles can be set directly on the concrete but unless you want a very thick bed of mortar, the cement board is the best material to use for a build up. It depends a lot on the thickness of the carpet and pad you plan to use
There are also metal beads for outside corners, edges and a ramp shape for floor transitions if you want to go that way.
As long as the concrete floor is in good condition, probably any thinset will hold it in place without nailing, it is just a small area (<30SF) with little traffic afterall . Premium thinset will bond better but a bit overkill IMO. Concrete bonding adshesive painted on the concrete before mortaring would probably help as well especially if the concrete is presently painted. If it is open clean concrete, you could use masons mortar (under the board, not for the tiles) and be OK. This is not as critical as setting stone on a cieling, gravity and similar materials will all work in your favor here. With no risk of floor deflection, you don't need a flexible mortar either.
1. No, a membrane would prevent the thinset from sticking to the concrete. Tapiing the saems is unnessary sionce the underfloor cannot deflect. Just smooth it over with some thinset until you are ready to set the tile. Fiberglass tape won't hurt if you have some. Tile and thinset are a moisture barrior.
2, No, just stick it to the floor
3. Build a mockup using a sample of tile, plywood and a sample of carpet and pad. Stack it up and see how it looks. Given the thickness you described, it will probably be fine with 1/4" board. Add the tile thickness to ~1/4" of thinset plus the board thickness and ~1/8" thinset under the board for an estimate.
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PipeDown wrote:

ever use a bucket of vynal glue on ceramic tile on concrete?
looks like it would never come up (not without a crowbar)
(its my secret weapon)
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