"RicodJour" wrote in message
...
On Oct 22, 10:46 am, "Sammy bin Snoozin"
wrote:

I see. My building vocabulary is not that good. It
already has 2x6 boards on the joists, if that's what
underlayment is. They are in good shape.

If you do not understand the terminology you will have a
tougher time
asking questions and deciphering what is meant by the
answers. Google
'construction glossary' and you'll find a good place to
start to fill
in the blanks.

Underlayment is a plywood (or approved equal) layer on top
of the
subfloor. In a typical tiling situation the house might
have 3/4"
plywood or OSB as the subfloor. The underlayment is meant
to smooth
out the surface in preparation for the tile. If your
subfloor is
strong enough you don't need an additional underlayment -
you can bond
the cement board directly to the subfloor.

Well, thanks....it's been a month since I posted the
question. Since then I learned some of the terms, already
installed the cement board - like you say, directly to the
subfloor. (I'm not laying tile, by the way).

I don't understand how you could have 2x6s as a subfloor
unless your
joists are spaced far greater than the typical 16". Tile
installations live and die by how much the floor will
deflect under
load. If you subfloor or joist spacing is unusual the
normal advice
doesn't apply.

Too late -- the floor's already fixed, but they were
tongue-in-groove 2x6's. From what I gather, it's std 1961
tract home construction. Again, no tile invovled.

Post pictures on one of the free hosting sites and link to
them in
your next post.

R