[JazMan]

You do not install Ditra over CBU, one or the other.

Tell us how the framing and subfloor is built, including species and grade of the joists if possible.

Jaz

 

[JazMan]

OK, 5/8" is very cheap a** of the builder. The fact of 2 x 10" joists means nothing without the span.

Need the whole thing. Please add the spacing of the joists and the span to the inch. The grade would be helpful too.

Jaz

 

[JazMan]

kiteman,

You're correct that;

The span tables for here say that grade and spacing is good to 15' 5".

But, you're not considering the correct type of flooring. That spec, (40lb/10lb live/dead load), is good enough for vinyl or carpeting, It's not so good for ceramic tiles. I recommend you use 50/20. :thumbsup:

So, if these are regular SPF (not south), you meet minimum at about 13' 0". That of course is if they're installed correctly and still in perfect condition.

So. you gonna add another layer of underlayment? What type of tile backer will you use?

Jaz

 

[JazMan]

5/8 t&g plywood as a subfloor does meet minimum specs in home building, but it scares us to install a quality floor over it. Schluter also says 5/8" ply exp. 1 subfloor grade is ok, but it still needs to meet L360 deflection specs. Do you know if it does? How you gonna check?

It's best to install an underlayment grade ply over to stiffen it up a bit. The thinnest you can consider is 3/8". But I recommend min 1/2" preferably thicker. The more the better. So the 1/4" stuff you have belongs at the curb.

Todd thought your underlayment was luan since it used to be a common product to use under vinyl. Yes, luan will delaminate fast if it gets damp. You never ever tile over luan.......ever.

Jaz

 

[JazMan]

How you add the bench only changes the centering of the drain. What's the size of the floor less the bench and where's the drain?

Jaz

 

[JazMan]

Most showers I've done go in with a curb. I've always framed or used concrete blocks, covered with tile backer as needed then waterproof with Kerdi, a few time liquid membrane. I've never used Kerdi board to make a curb less shower floor.

The last time I used 1/2" Kerdi board on shower walls, I later wished I had used 5/8" instead. It actually works better to transition to installed drywall. Stiffer too.

I only watched as a bench, (not shower) was built when I attended the workshop at The Ceramic Tile Education Foundation in '09.

Jaz