I was trying to prep my bathroom floor for tiling and decided to use Killz on the floor due to mildew and molds after ripping off the vinyl. I did scrape off all the adhesive and particles stuck to floor before applying Killz. I wanted to waterproof the floor and apply a sealer to preserve the concrete. After talking to two guys at home depot, they told me that Killz was the wrong product to use on the floor prior to tiling and suggested that I buy a floor stripper to remove Killz. I find that a bit odd because Killz didnt change the surface of the floor much and the argument that the two guys from Home Depot raised is that the tiles wont stick to that surface. Is this true? Do I need to strip off Killz from the floor? Can I just add something else to make the surface suitable for tiling? Please advise. Thanks.

I have never tiled over a painted concrete surface, so I can't tell you the results. But I learned a long time ago from pro tile setters, that if there is any paint on the concrete, it must first be removed before the tile goes down.
So I like to think I learned the 'easy way'. And that's just a practice I continue to use. And I'm real clear with the drywallers and painters about that situation before they get started, that the floor requires protection, and to include that in their bid.

Thanks for replying. I really appreciate your input.

So I guess I am going to learn the hard way...but at least the bathroom floor is not that big in size.

What kind of solvent or product can I use to clean off the mildew off of the concrete floor prior to tiling?

I found this solution from another website and would like someone's input or feedback on it.

Please read the answer given to Les from the floor expert. Thanks.

Advice On Painted Concrete Surface

Keep in mind - all message boards (including this one) have people who know what they are doing and people who think they do, but don't.

Don't paint the floor. If there is paint there, strip off as much of it as you can. Kils is certainly not the right product for a floor sealer. if you are worried about mold, then kill the mold with a bleach based product. Rinse well and let dry. Then install your thinset and tile directly on top of the concrete.

Good advice on the bleach...that's what I should have done in the first place if I have known that paint is a no-no for tiling.