Tiling over existing thinset

Old 03-21-17, 10:37 AM
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Tiling over existing thinset

I am replacing the tile in my kitchen and am wondering if I can smooth the existing thinset rather than scrape it down, then add the new thin set and tile over that. My house 30 years and is over a basement. I think the tile is 12-15 years old and previously the house probably had vinyl flooring. My current subfloor has to layers of 3/4" plywoood with cement board installed with thinset and nails. I am using a hammerdrill to remove the tile. I tried to remove a section of the cement board but it was very difficult. I tried to scrape or smooth the thinset down to the cement board with the hammerdrill and hand scraper, but dug into some of the cement board. Both were difficult time consuming. Both the cement board and thinset seem pretty solid. As I don't want continue to damage anything else. Can I smooth over the existing thinset with floor leveler or new thinset, then add the new layer of thinset and tile? My newtile will be 12x24. I also have a few low spots I will need to level out anyway.
Old 03-21-17, 10:53 AM
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If the substrate and thinset is solid then you can go over the top with new. The big issue is going to be the smoothness. Without a somewhat smooth surface it will be difficult to properly trowel out new thinset. This could lead to difficulty getting the new tiles level and fully supported by the new thinset. Another issue I've run into is if a bit of the old thinset breaks off when troweling on the new. The chunk, if not removed, holds the tile up and prevents you from leveling it or mushing it down properly to bond into the thinset.
Old 03-21-17, 04:26 PM
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With tiles that big you will have to back butter them which will help but fully agree removing the mortar is best approach. Even gouges in the CB are preferable to rough mortar.
Old 03-22-17, 01:16 PM
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Yes you can prime and self level if the existing mortar is well adhered. I have done it may times to smooth out mud beds for reinstallation of new tile. Large format tiles need a super flat floor so keep hat in mind as well.

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