John Grabowski wrote:

"Dante M. Catoni" wrote in message
...
My bathroom floor is constructed as follows from the bottom up
2" X 8" joists 16" on center
3/4" X 7" boards running perpendicular to joists
1/2" x 7" boards running parallel to joists (very wavy)
3/16" plywood?
ceramic tile

Within a few weeks of buying this house the tiles started cracking and
the grout popped out. I just took out most of the tiles by hand.

I was planning to remove the 1/2" boards and put down
5/8" exterior grade plywood
thinset
1/4" Hardibacker
then tile again

The floor will end up a little higher than it is now which is about
even with the hall, but it might still be ok. Would it be better to go
down to the joists and start with 1" ply? If I put thicker plywood on
the joists can I go directly to cement board or are there two layers
for a reason? Is there anything else I should consider? I want to do
the job right and make it last.


*It sounds as though you have a decent subfloor. What I would look at
is the joists. How long of a span do they have without support?

Something else to consider is that the previous owner may have put down
a fast and cheap tile job to sell the house. The tiles may be popping up
because they were not installed properly.

Had almost the same substructure you have when I did a bathroom tile
floor about 10 years ago. If the 1/2" & 3/4" boards are relatively flat
you can screw all of them down tight to the joists and even take out
some of the humps at the same time. Lay a layer of mud and 1/2" cement
board on top and screw it down. While you are screwing it down you can
really tweak the floor and level it out as the mud will hold up the
cement board in the low places once it dries. I put a latex additive in
the mud which supposedly added gripping power and made it less
susceptible to cracking. Used the same additive when it came time to
put the tile on top and haven't had a bit of problem with cracking.
Suspect as someone else said it might have been a quick job just to make
it more sellable. Just my 2 cents