Bathroom Floor [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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01-12-2003, 07:48 PM
I am attacking a water problem with an upstairs bathroom. The 1" square mosaic floor tile which was 15 years old was shot. Water had been leaking through for quite sometime. Stains on the ceiling which had been painted over.

I have removed all the tile, except for under the toilet (which I will do after I pull it). The bathroom area to be tiled is only 36 sq ft. I think I have 3 questions, maybe more.

First, there is a small cabinet, holds the sink, and the tile is under this also, but the edges on the tile only stick out 1/4 inch. Do I need to pull the cabinet and tile everything?

Second, the wall has a tile baseboard which is in good shape. Should I pull this, or can I put down additional plywood and cement backerboard and build up beside of it?

Third, the floor is plywood, can't tell how thick but very sturdy (doesn't bounce) except in a corner that is bounded by the tub and wall (where the water damage is). It gives when I step, discolored, and is kind of brittle. This area is about 12" x 18." Will plywood (1/4?, 3/8?) and backerboard across the whole floor strengthen this enough so it doesn't flex? It is right where we step in and out of the tub.

Thanks, any help would be most appreciated.


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Andy Lester
01-12-2003, 09:39 PM
Have you determined the source of the leak? Toilet? Shower? Tub? Before going any further you should try to determine where the problem is coming from. I will attempt to answer your questions, but first, I suggest you pick up a copy of the newest Tile Council of America Handbook on standards for ceramic tile installation- it contains many of the details related to proper floor thickness, etc. Go to You should also pick up one of the good tile books out there, such as the one by John Bridge (forum moderator) or Michael Byrne. Both are available from and offer a wealth of information on proper installation methods.

1) Yes, you will need to pull the cabinet and the sink (and the toilet) to properly re-tile the floor. Even if you had enough perfectly matching tile to work around it, it's a big pain. I would take everything out.

2) Does the floor tile run underneath the "tile baseboard", or does it meet it? You can probably leave this in place, but without seeing it I can't say for certain. Either way you will need to include movement joints where the floor tile meets the wall.

3) This points to larger issues... at a minimum you will need to replace this section of plywood, and verify that the joists beneath are still sound enough to hold new plywood (and tile). It seems like there's a leak related to the tub (is this a tub/shower?) But like I said above, try to determine where the leak is coming from before proceeding any further.

It seems this is a plywood subfloor- when you're removing the current tile, are you pulling the tile off the plywood or simply taking everything out down the the joists? After correcting the leak, you will probably need to remove everything down to the joists, and then install 5/8" exterior grade ply followed by 1/2" backerboard (to reach the 1 1/8" minimum floor thickness). What is the size and spacing of the joists?


01-12-2003, 10:39 PM
Covering a potential problem does no good.

I would remove the cabinet, the tile baseboard, and repair the substandard floor beore proceeding with the tile.

Once the leak is fixed and the subfloor is fixed, prep / tile on!!!


01-13-2003, 06:35 AM
Thanks for the advice. I have determined, I hope, the leak was coming from the area of floor tile where the water damage is. Last year I replaced the tile around the base of the tub, and it still looks good. We also tried to be very sure the shower curtain was in place. No leaks for months and then a spot reapeared in the ceiling.

I started examing the floor and found it mushy. I poured water on the spot (don't laugh) to see of I could tell where it was going. I couldn't see a specific spot, but the water just soaked right through, a couple of cups worth. We have continued to use the toilet, with no leaks. The spot in the ceiling is not directly over the leak, infact its not over the bathroom. I am guessing it is just running downhill before pooling.

Not sure the thickness of the plywood floor and the spacing of the joists. Probably have to wait for the weekend. There was nothing under the tile but plywood.

Not sure how to cut along the base of the tub and wall in order to get the peice of rotten plywood out, but I will think of something.

Thanks again


01-13-2003, 07:09 AM
John, Rent a toe kick saw. Now,as for subfloor.Use a good quality 3/4" Plywood.Followed By either an SLC or CBU.
5/8 Plywood with CBU lacks the strength as CBU adds no structural strength to your floor.Given the room,i would go for 2 layers of plywood.3/4"+ 1/2" + 1/4" CBU
Once you have your entire subfloor installed, If you are concerned about moisture problems,You could use a paintable waterproofing membrane over the entire floor and up the walls an inch or 2.C-Cure Prored 963 is easy to work with and for your small area a gallon would be more than sufficient.
I'll keep an eye on your progress!!!!

ok gotta run,gotta couplea miles of quarry tile to put in as cami so elequently put it :)