For a bathroom project, I plan to use backer board on walls and floor.
Backer board used on walls will go directly against studs and for the
floor it will lay on top of 3/4" ply. My local warehouse store carries
backerboard only in 5/16" and 1/2" sizes. Due to size restrictions and
other issues, I'd prefer to use 5/16" for everything. Can anyone see a
reason why this would be a problem?

A DIY book I was reading said the floor should be at least 1 1/8" thick
using backerboard no less than 3/8" (over ply). I'll be 1 1/16" total
thick with only 5/16" backer board. 1/16" isn't anything to worry
about, right?

Thanks for your opinion.

"Mak Wilson" wrote in message
oups.com...
For a bathroom project, I plan to use backer board on walls and floor.
Backer board used on walls will go directly against studs and for the
floor it will lay on top of 3/4" ply. My local warehouse store carries
backerboard only in 5/16" and 1/2" sizes. Due to size restrictions and
other issues, I'd prefer to use 5/16" for everything. Can anyone see a
reason why this would be a problem?

A DIY book I was reading said the floor should be at least 1 1/8" thick
using backerboard no less than 3/8" (over ply). I'll be 1 1/16" total
thick with only 5/16" backer board. 1/16" isn't anything to worry
about, right?

Thanks for your opinion.


1/2" on the walls and 1/4" over proper subfloor on the floor. You decide if
the 1/16" is important or not. I find that following or exceeding the
minimum recommendations usually gives the best long term results.

Colbyt

If I could find 1/4" for the floor I might use it, but so far nothing
local can be found.

It's so tight I won't know until I try it, but I think I can get away
with 1/2" on the walls. I guess that will offer better support
considering there'll be nothing behind but the studs. Thanks for the
reply.

I believe the floor thickness of 1 1/8 refers to the total thickness of
the subfloor (excluding the baker board). What is between the plywood
and joist? The concern to how much flex the floor has. If the 3/8 on
the floor is solid when you jump on you probably okay.

There is nothing between the plywood and the joist. In my case the DIY
book I have (Ceramic Tile by Creative Homeowner sold at my local Big
Box store) it's clear the reference is for the total thickness of
subfloor and underlayment. Whether or not the book is right is open
for debate, but your jump test seems like a good idea either way.
Again and for the record, I won't be using 3/8, I'll be using 5/16 but
I think your point is the same. Thanks for your thoughts.

Try this site for your question: www.johnbridge.com

You'd better double check what your book says. I'm pretty sure the
NAtional Standards for ceramic tile require 1 1/8" thickness of
subfloor (i.e. plywood) to prevent any movement. Even 1/2" Hardibacker
doesn't provide any significant structural support, so including it in
the 1 1/8" could lead to cracked tiles down the road. Since you have
space restrictions you could make the floor stronger by adding 2x6
supports perpendicular between the joists. And do apply thinset under
the backer board for added stability.

I have checked my book. It not only states 1 1/8" total thickness but
even shows it in an illustration. Perhpas I'm confusing terms and
that's getting me into trouble. My understanding is that the SUBFLOOR
and the UNDERLAYMENT together must be at least 1 1/8". I thought the
backerboard counted as underlayment. If it does not then that's where
I'm wrong. Can anybody clear this up for me?


Here's Home time's definition of the 1 1/8" which again seems to
suggest 1 1/8" total including the backerboard which they (further
down) describe as underlayment.
http://www.hometime.com/Howto/projects/ctile/tile_4.htm