I am attempting to replace carpet in a half-bath (toilet & sink only) with ceramic tile. I've done a little ceramic tile work before but am still basically a novice.

When I removed the carpet and pad, I found that the floor is just a single 3/4" layer of plywood. Further, the top layer of the plywood floor is delaminated (split along the grain and raised) in places.

I've read numerous posts on the Internet that say that you should have a minimum floor thickness of 1-1/8" for tile, and that the best surface to use is cement backer-board. However, I'm not sure how to apply that advice to my situation.

My questions are:

1) What do you recommend to prepare the floor for laying ceramic tile so as to minimize the height of the new floor (it abuts a carpeted hallway and I don't really want people stubbing their toes entering the bathroom).

2) Whatever new layer you recommend, can I apply it directly on the existing somewhat-damaged plywood floor, or do I need to tear up the existing plywood and put down a new subfloor?

Thanks for your help.

De laminating means the layers of plywood are coming apart. What you described sounds more like cracks and shrinkage of the outer ply or layer. It happens the grade of plywood used for flooring. If that is the case just put the 1/2" cement board down and install the tile. That should put you at just about the same height as the carpet.

I agree with Harold but would use 1/4" Hardiebacker which is screwed and glued to the ply. Spread modified thinset with a 1/4" square notched trowel and then lay the borad and screw every 6" in every direction.

Why 1/4 Bob? I usually figure 1" for carpet and pad.

1/4" backer ends up 3/8, then 1/4' of thinset and a 1/4 tile = 7/8", carpet compresses a little so we aren't trying to be even with it.

These guys are both correct. There is one more option, and that is to use ditra membrane. But, if you have some imperfections in the floor, patch them first, then you apply some thinset, with ditra on top.

It's an orange membrane, but it's a bit expensive, so it might be better to go with what Ball and Harold suggest. The do have a 1/4" wonder board and it's easier to cut. There are also some thinner "pad like" options, but I cannot vouched for them because I have not used them.

You already have some good advice. If you do use wonderboard (thin cememt board) check your door measurement at the bottom of the door to make sure the is room to open after applying the measurements Ball and Harold gave you. You may have to shave or cut a bit off the door.

Add: One more thing... make sure this is real real ply and not that part. Board often used for carpeting sub. You want to ensure that this ply is also not loose anywhere. Walk on it and secure it so that it will not move or bounce.
Good luck.

A foot note here. Should you bath floor end a little high there are marble handicap thresholds available. One edge is beveled to make the transition. Probably have to go to a tile outlet like Dal tile to find.