tiling existing slab

10 years ago

we have exposed concrete floor in our house that we would like to tile. when the house was built we asked for concrete to be a finish floor so it is very level and smooth. it is sealed with solvent based sealer. now i understand that sealer needs to be removed, unless you guys tell me different.
also during first month the slab developed hairline cracks maybe 1/16" thick here and there and concrete is level going over the cracks. do i need to worry about them? the slab is now 5 years old and there were no additional cracks developing or any other problems.
after i remove the sealer, can i just lay directly over the bare concrete? for removing sealer on part of the slab i have used chemical that i dont remember the name but it seemed to remove it good as when i spilled water after it would soak in within minute or so. before it would sit on the sealer for at least 5 minutes. i am just hoping i dont need to use scarifier.
also what groutline thickness is recomended for 12x24 tile. i would like the thinnest. 1/8" ok. and what trovel notch size?
any help appreciated

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Comments (3)

live_wire_oak
10 years ago
The concrete needs to have the sealer ground off. Chemicals drive the sealer further into the slab and interfere with the adherence of the bedding mortar. You need rectified porcelain tile with a medium mud bed (NOT thinset) to lay large format tile with a small grout line.

This is NOT a DIY job unless you are a very experienced tiler. Even then, you'll have issues. All large format tile installations even by pros have some issues because the floor isn't usually as flat as people think it is, and because of the inherent nature of the tile having a bit of a droop that translates to lippage. Thus the recommendation to do the medium bedding mud rather than thinset by manufacturers. It's easier to address lippage that way.
brankulo
Original Author
10 years ago
oak,
i have installed tile in my previous house over concrete floor and it went fine. i also did both showers. the tilesused were smaller 12x18 vs 12x24 i am installing now. i used thin set. the sample for this 12x24 tile says to use latex modified thin set too on the back. it is rectified tile. i am not sure what you mean by lippage.
thanks for help
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StoneTech
10 years ago
Live Wire is correct about the sealer being driven into the slab. It needs scarification.

As to the cracks...Horizontal displacement can be addressed while vertical displacement precludes a tile floor, it just does. If the former, I would Ditra or Greenskin the floor, assuming it's flat. Variation shouldn't be more than 1/8" over any ten foot span...or you'll need to grind/fill to achieve this.

Both of the above products act as a decoupling membrane to accomodate any lateral movement and cracks developing in the tile.

Measure the smallest and the largest tiles you can find. Whatever the size variation, multiply that by three. That number is the MINIMUM grout width that can be used. (1/8" variation equals 3/8" minimum joint)

Smallest trowel is about 1/4x3/8" Try that, put down a couple of tiles and remove one to check for coverage....shoot for 100%....80% is acceptable. If less than that, move up one trowel size. "Flat Burn" the tiles before setting....