I moved in a apartment building built around 1992. It currently have carpet for the flooring that installed by the builder. I am thinking to lay ceramic tiles in living room so I removed carpet. What I found underneath is concrete subfloor with some kind of white paint on it. I am not sure why the builder paint the subfloor before carpeting it? Most likely what is this white paint, is it some kind of primer? Can I use thin set on it directly, or should I use a paint stripper to remove it?

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    It is possibly a waterproofing membrane or moisture barrier if it is a ground level or basement concrete floor. Depends on its makeup, whether it is cementitous or not will depend on if you can go over it or not with tile. Most likely you can but need more info for a good answer. First thought, do not remove it. – Jack Mar 26 '17 at 6:20
  • It would be a huge and very messy job to remove that coating to get down to bare concrete. And then you must prep the concrete for thinset for ceramic tile. Consider a floating floor of prefinished hardwood/engineered wood, i.e., a floor which is not adhered to the coated concrete. Where is this apartment located? – Jim Stewart Mar 26 '17 at 10:16
  • @Jack the best I can tell about the paint it feels porous. – xbtsw Mar 27 '17 at 4:28
  • As I removed more carpeting I realized this paint is not intentional, I think it was the splash of them spraying the patterned ceiling. – xbtsw Mar 27 '17 at 4:48

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