6mm ply under tray former to make my levels correct?

[ollymonkeynuts]

Hi, Over the main bathroom floor im using 18mm WBP over joists with added noggins. On top of that will be 10mm Marmox board on a 2mm addy bed. Total 30mm.

The shower tray is a AKW tuff form tray (22mm). I wasnt going to put UFH over this tray just over the rest of the floor but looking at the levels if I was to put 6 or 8mm ply under the tray it would bring it in line with the rest of the floor. Then I could UFH and SLC over the whole floor.

If this ply is correctly primed (under & edges) would it be OK?

The other options are a) is not to have UFH over the tray, just to lay 18mm ply over all of the floor, put the tray onto this, then elsewhere 2mm addy, 12mm Marmox, 3mm UFH under 4-5mm SLC.
b) lay the tray direct to the joists then dont use Marmox just lay the UFH onto the ply and 1mm SLC to get it to the tray level.

Which would you do? Thanks.

 

[Ian]

Why not use 6mm cement board to help get your levels correct, ply that thin is far too risky in a wet environment IMO.

 

[ollymonkeynuts]

Why not use 6mm cement board to help get your levels correct, ply that thin is far too risky in a wet environment IMO.

Thanks, i was thinking the ply would be a bit susceptible at that thickness. 6mm cement board could be the answer.

 

[ollymonkeynuts]

Ive ended up going with 25mm WBP and will use 18mm WBP under the Tuff form tray, this will leave the rest of the floor 2-3mm above the tray. Better that way for drainage. Sorted. I doubt there will be deflection issues after the 25mm is put down, its proper sturdy stuff!

 

[White Room]

With the tuff 2 former I sat on joists with extra noggins after removing a section of the floorboards....

 

[ollymonkeynuts]

With the tuff 2 former I sat on joists with extra noggins after removing a section of the floorboards....

Even when the tray is 22mm thick Im not convinced it wouldnt give a little over time as its plastic. Im learning to be 'better safe than sorry' when it comes to tiling rather than my normal 'a short cut is a good cut' attitude. Ive just ordered £350 of marmox! im taping all the joints not just in the wetroom shower area, stainless screws.....etc etc.

 

[PHG Dave]

Even when the tray is 22mm thick Im not convinced it wouldnt give a little over time as its plastic. Im learning to be 'better safe than sorry' when it comes to tiling rather than my normal 'a short cut is a good cut' attitude. Ive just ordered £350 of marmox! im taping all the joints not just in the wetroom shower area, stainless screws.....etc etc.

Good to hear you're doing the job properly
Re the use of ply under the tray, if you had still been planning that route then it should not have been a problem as no water/moisture should be getting under the tray or associated waterproofing. If it does then you will have a lot more to worry about than than ply de-laminating!