Tile over cement slab

Old 05-06-05, 03:33 PM
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Tile over cement slab

Thanks in advance for any advise you can give. I would like to tile (12x12 porcelin) a part of my cement basement floor. The floor to tile, about 25ft x 14ft, is about 20 years old with a small hairline crack. Water has never been an issue. It has never been painted or had any other type of flooring on it. It is as smooth as glass with minimal slope to a floor drain at one end. I don't know if it has ever had a sealer put on it. What type of floor preparation will be needed? Do you recommend thinset for this application? What would you suggest?
Old 05-07-05, 11:10 AM
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Splash a glass of water on the floor here and there (where you intend to tile) and see if it beads-up or soaks in, first of all. If it beads then more than likely the floor has a sealer but to tell you the truth I would doubt it, especially on a floor that old. If it does have a sealer then the sealer would have to be removed mechanically before you could expect the tile to stay.

Next is that hairline crack and the definishion of "hairline".
If the crack has noticeably opened and closed with seasonal changes then you may not be safe in simply tiling over it.
It would be a good idea (considering the cost of the investment) to address that crack with an isolation membrane material of some kind.

Thinset would be the only thing to use for the adhesive, "Modified Thinset".
Old 05-08-05, 07:24 PM
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Thanks for the info! The crack does not seem to change, but I would rather be safe than sorry. Does Lowe's carry this isolation membrane or will I need to go to a tile store? Is it only necessary to cover the crack or would it be better to cover the whole floor with the membrane.
Old 05-09-05, 09:54 AM
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There are several crack isolation products available. Check your local tile stores for Noble CIS, Protecto wrap or Laticrete blue 92 Anti fracture membrane (might be at Lowes) or Redguard at HD. IF you use the Redguard, you will need to get 6" fiberglass drywall mesh tape and embed it in the first coat of redguard and then apply a second coat. Usually the minimum estension of a crack suppression membran is at least the diagonal measure of a tile on either side of the crack but it may be more depending on what you use.
Old 05-09-05, 05:20 PM
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Thanks for your help!

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