"Abe" wrote in message
...

"Abe" wrote in message
.. .

So I talked to him, he said he'll use 1/4 hardy board. He said it's
like a cement board but the particles are finer. I asked him if he can
do 1/2 hardy (or cement) board and he insist those are used on walls
and not on floors.

He did not talk about a layer of plywood under the bardy board, and I
didn't ask him either since I am just reading this now. Is a 1/4"
hardyboard enough? How important is the plywood layer? He said there
will be another layer of cement (thinset) on top of the board so
having a 1/2" cement board is too tall.

No, the hardyboard alone is not enough. You need 3/4" structural
plywood with a sanded face underneath it. A vapor barrier should go
between the subfloor (shown in your pictures) and the plywood. The
plywood should be screwed down or nailed down with ring shank nails
every 8 inches in all directions. The hardy board 3/8" or prefereably,
1/2", not 1/4", is then screwed to the plywood (nails are not used
here). Then the tile is set with the proper setting material on top of
the hardy board.

You left out a decoupling membrane
How can you know what he needs if you dont know the joist spacing?

I'm assuming standard 24" O.C. joists. You're right, I shouldn't
assume.

Thanks. Thats explains why I thought most of the floor advice I saw was way
thicker than needed. My joists are 18".