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I'm looking to replace an old carpet in my finished basement with tile. I've removed the carpet and found a surface with some peeling paint, which I've read needs to be removed since the thinset for the tiles needs to bond to a solid surface.

I've tried attacking a small area with an angle grinder with a sanding attachment and a coarse grit sanding disc, and I've found that there seem to be a number of layers on top of the slab:

slab after grinding an area small 3" area

It looks like there are at least two layers of paint, and then the green layer is pretty resistant to coming off. Below that there is this red, which I thought at first was maybe some weird color of cement, but if I really leave the grinder there it seems to get through to gritty looking concrete.

What do I need to do here to be able to tile on top of this? It seems like the green / red layers are very well adhered and I wouldn't be worried about them coming up, but they also will not absorb any water, so I'm not sure if the thinset would bond?

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That's a strange problem indeed. What kind of tile did you have in mind? –  Lars Dec 7 '12 at 4:34
    
Ideally slate, but I haven't fully decided yet. If not, then likely normal ceramic tile. –  Paul D Dec 7 '12 at 5:14
    
How would you feel about adding a layer of subflooring to give you a smooth clean surface to tile over? –  The Evil Greebo Dec 7 '12 at 16:07
    
What would that involve? –  Paul D Dec 7 '12 at 17:32
    
If my Googling serves me, that'd essentially be framing a floor with 2x4's and covering that with plywood. I'm not sure I can afford the to lose 4" of height without it starting to be a little too cramped. –  Paul D Dec 7 '12 at 17:40
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2 Answers

up vote 2 down vote accepted

Putting tile over a painted surface can be risky. Sure looks like removing all that paint would be a chore and maybe hazardous (lead based paint if pre 1978). We have put tile over such surfaces by roughing it a bit and putting a scratch coat of "floor patch and leveler" over the entire surface. This is a good bonding agent on stable subfloors.

Another very good alternative is to use one of the new no-mortar interlocking tile products. These are tiles mounted on an interlocking plastic base that just snap together. They are very quick and easy to install. There are several different brands, tile material and backer types available. There is an article about these type of tiles, on Good Housekeeping.

Google "no mortar tile". Lots of articles on the subject

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I did use a lead check kit and wiped the test unit over all the various layers and it came up clean. I think based on your answer, I may grab a grinding cup to replace my sanding disc, and try and remove as much as possible, then use the leveler. I was likely going to have to do that anyway, as the existing floor while pretty flat isn't as flat as the 1/8" over 10ft span requirement for slate tile. These conrete-based leveler compounds should bond OK even though the surface will probably still be pretty non-porous? –  Paul D Dec 7 '12 at 16:04
    
yes, it should bond well. We use it over vinyl, tile, whatever. As long as the base is stable, the leveler allows you to lay new tile over it. –  shirlock homes Dec 8 '12 at 11:13
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I wouldn't bother with the floor leveler, there is no need in introducing a second product that needs to bond to the paint. Rent a rotating floor buffer with 18 sanding pads rough the surface up the best you can. If it's that difficult to get up it will be fine, the only issue you might have is if water gets on it. Which will be a problem if you use self leveler too. If the paints bond loosens whatever is bonded to it will loosen as well.

Use a good quality thin-set such as ultra flex 2. Don't go for economy grade thin-set no matter what you decide. You want a good bond to the self leveler or the paint.

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