Flooring Tile - Ceramic tile floor in basement

I am in the process of refinishing my basement and was thinking of putting down a ceramic tile floor in the new bathroom. Do I need to build a sub floor before tiling or can the tile be put directly over the cement floor that exhists now. I don't have water problems (not yet), but do need to consider moisture problems in the summer. The floor seems to pretty level. Any recommendations on quality of tile, adhesive, grout and sealer to use as well?

You can tile directly to the concrete slab. The concrete slab must not be painted or sealed. You can check to see if the slab has been sealed by putting a few drops of water on the slab and seeing if the water absorbs into the slab. If you have any cracks in the slab they may have to be addressed. Post back and let us know.:)

OK. Unfortunately the floor is sealed and painted. What are my options now?

Rent a floor grinder and remove the sealer and paint. No chemical strippers.

I will try that. Thanks for the advice.

I found this on the subject:

Q: I'd like to tile my basement floor, but there's a coat of paint over it. Someone told me I'd have to sand the paint off. Is there any alternative that's not so messy, or should I go to another type of flooring?
— Daniel, Mineola, N.Y.

A: Joe Ferrante replies: Sanding would be a big mess, that's for sure, and even then you can't be sure the tiles will hold. Here's what I would do.

Scrape off any loose paint, then scuff up what remains using a pole sander and 80-grit paper. Vacuum up the dust. Now use a notched trowel to spread thinset adhesive mixed with a latex additive over a section of the floor. Place a sheet of 1⁄2-inch cement board into the adhesive and beat it into place with a wood block and a hammer. Keep spreading thinset and bedding sheets of cement board until the entire floor is covered. Be sure to stagger the boards and cover the joints with a layer of fiberglass reinforcing tape and thinset. Leave the floor alone for several days, then tile it following standard methods.

Even if the bond between the thinset and the basement slab eventually fails, the boards will "float" in place and the tiles will stay secure.

Joe Ferrante is a tiling contractor in Massachusetts


I will probably try this in my area, since it is pretty small, 5 x 9.5 bathroom. It is definately not ideal, but it may work for some applications.

Wrong wrong wrong - no cement board over a concrete slab.

Johnny is absolutely right. I have no idea where that guy from Mass came up with that method but it is not approved by any tile trade association nor the manufacturers of the cement board. Ignore that post.

When do you ever put 1/2" on any floor? closest word I can think of for cementboard on a concrete deck is redundant.

When do you ever put 1/2" on any floor? closest word I can think of for cementboard on a concrete deck is redundant.


The closest word I can think of is failure, as in "Bound to happen".
The cement board must be mechanically fastened to the subfloor below it by means of galvanized roofing nails or backerboard screws, set at 6 to 8" intervals through the body of the board. Thats why cement board is only used over plywood subflooring. Some will say "How about Tapcons into a cement slab subfloor"? The heads of the screws must be set flush with the surface of the board, difficult to do with a Tapcon given the nature of their head, and do you really want to drive 60+ of them in per board? Then if the head countersinks it will tear through the board rendering its mechanical fastening ability useless. And then, if the board is not set in a bed of thinset to fill out the voids between the cement board and the subflooring then better off not putting it down at all.

1/2" can be used on a floor if you want the extra height buildup to transition to something else but otherwise it is not needed and does not offer any additional strength to the floor in place of a 1/4" cement board, which is lighter and easier to handle.

More confused than before!!! I am back to square one and having to rent a floor grinder? Can't I just put down new plywood floor (1/4"), cement board and then tile?

Sorry to add to your confusion. I would normally follow the manufacturers recommendation. Joe Ferrante is the tiling contractor on "this old house", search his name and tile. This Old House is not exactly known for cutting corners and doing things the easy way. You should give Joe a call and ask his opinion, he is in Linwood. I may still try it and if it fails its my own fault. I have a couple of months to decide.

More confused than before!!! I am back to square one and having to rent a floor grinder? Can't I just put down new plywood floor (1/4"), cement board and then tile?


Grinding is the most practical option. Paint and sealer will inhibit the bond of the thinset to the slab floor, in fact the thinset wont even be in contact with the concrete, it will layered over the paint and sealer. If the thinset wont bond with tile over it, what makes you think it will bond with a cement board over it. Thinset is not used as a bonding agent under the cement board in a normal application, the nails or screws do that and the manufacturers warranty calls for them to be used. The thinset under the board is also required by the manufacturers and is used to fill open voids between the cement board and the plywood subloor , which if left unfilled could cause the tile to crack when subjected to a point load weight condition where the tile is not strong enough to support the weight above it over the span of that void, so it cracks under the weight.


You cannot put plywood down directly on the cement floor, it needs to be screwed into some wood framing that is set at 16"O.C. joist spacing and anchored to the floor. The plywood would have to be 3/4" BC grade exterior glue, then you could put a 1/4" cement board over that. This would be at the minimum for a floor to be acceptable to set tile on as per the Tile Council of North America in their Handook for Ceramic Tile Installation. Anything less or anything improperly done will set you up for tile failure down the road.

There are no tile police, only the practices in the book mentioned above, so you can do whatever you want. Johnny, myself and a few others use the methods outlined in the handbook when giving advice but if you choose to use a home brew remedy, which may work fine in certain instances, you can take the credit if it works out and you can trake the blame if it all falls apart.

Thanks all of you for your advice and tips. I end it up going "old school" and got on my hands and knees and sanded the paint off with 16grit sand paper. I was able to get 5" wheels to fit my hand drill, which made it bearable.

Took me a couple of hours, but did the job. Now I could use some advice on what kind/grade of cement and tile I use use. Any thoughts?

Use a high quality modified thinset. Tec's Full Flex or Super Flex are great. Custom's FlexBond sold at HD is also very good.
As for tile, go to a tile retail store where you will see a much larger selcetion and better quality than what is at the big box stores. Porcelain 12" tile will be very low maintenance at a decent purchase price.