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I have a concrete floor over which I would like to install ceramic tile. The only problem is that the floor has several coats of paint on it. My first thought was that thin set would not adhere to the painted concrete, necessitating laying down cement board or some other porous substrate, adding expense, and raising the floor height. This option is not my first choice. A coworker said that I would not need to do that, that all I needed to do was “score” the concrete. I can imagine scoring the concrete with some kind of saw, but does anyone know of some other way to make this concrete more appropriate to use as a tile substrate? Any advice is appreciated.
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You would not need a backer board to adhere a portland cement thinset mortar to a portland cement slab. Scoring is not the correct term here as it connotes a different procedure for preparing the concrete for tile installation. The more apt term is scarify. As in to roughen the concrete surface.
You can use chemical or mechanical. Mechanical means is more in the realm of DIY. Use a belt sander with course grit or grinder with grinding cup or diamond blade.
No matter the method used in preparing the concrete for tile installation you will still have to address the concern of concrete cracking. Use a mat type slip sheet bonded to the concrete as a crack supression membrane.
If no active cracks, not too much worry; if you don't mind slight slab cracks propogating through the tile, no worries.
*Most backerboard manufacturers state that their products are not to be installed over a slab.And make sure the crack isolation membrane you use is compatible with the brand of thinset you use (check mfg instructions.)