Now the ply floor issues have been settled, I'm thinking it might be a good idea to use one of these mats?

Looking on the ditra site under the plywood advice section, it says...

' Butt joints must be tongue and groove and they must be glued'

I'm confused again, I thought a butt joint was where 2 square edges met so how can it be tongue and groove? So do I need to glue the edges of the square edge ply to make them stick together.....I saw advice elsewhere that said to leave a small gap.

If I do use a mat, does it go only on the area to be tiled and not under the bath or am I as well laying it everywhere to help with any potential moisture issues?

What else do I need to know about these things? Are they simple enough to use? I'm quite practical as long as I'm clear about what I'm supposed to be doing, lol.

(Ply floor will be 25mm and tiles are 300 x 600 porcelain in case it's relevant.)

The information given can be misread and I would agree to butt joint requires a square edges.
Unless the tounge and groove issue is one for the weyroc/chipboard style of flooring or indeed wood flooring boards.
I haven't followed your earlier posts so I'am not up with your progress so far.
Given that you have floor joists and are using 25mm plywood as your flooring grade substrate - is there any further covering going down before your ditra or other decouplig membrane. If not you will have t ensure that your plywood is solid without any movement.
For the amount it will cost to fully cover your room it may be worth going under the bath area and having a watertight situation.
Follow their advice on installation with a flexible fast set adhesive and 3/4mm 'v' trowel to stick the Ditra to the floor and overscreed the top with a flat trowel - again with the same adhesive.
Its a Great product and well worth the money.

Timeless John.

PS - Early finish today - rained off!!!!!!!

Ditra is a good product but Durabase Ci is cheaper...and is an un-couplig membrane as well.

Originally Posted by timeless john

Given that you have floor joists and are using 25mm plywood as your flooring grade substrate - is there any further covering going down before your ditra or other decouplig membrane. If not you will have t ensure that your plywood is solid without any movement.

No there wasn't going to be anything else. It's taken days of questions to get to the point where we laid the 25mm. Please don't tell me we should be doing something else.

I thought the 25mm plus extra noggins was ok? What else should we have considered?

I'm a bit like this right now > .

Think I'm opting for the Durabase. Best place to buy?

I think one of our sponsors, Wetdecs, supplies it Gill
http://www.diy-wetrooms.com/