Setting wedi shower on plywood base. - Tile Advice

[PeteBristow]

Hi Folks,
if I could pick your brains for an opinion Id be very grateful.
I'm building a bathroom over here in NL In my attic.
Ive battoned between the floor joists, and set 2 layers of 18mm plywood under the shower area. I primed the plywood with a waterproof primer, then set the wedi fundo Rialto shower tray on a layer of wedi 320 tile adhesive.
I ensured it was level then set some weight on it until it was dry, and didn't step on it for nearly a week.
As I was preparing the wedi boards for the walls I noticed the wedi cement beneath the shower tray had cracked and the tray wasn't bonded to the plywood anymore.
If I press on the shower tray I can see a tiny bit of movement between it and the floor, so I plan to lift it this weekend (I don't think I have any choice, had, for a tiny moment considered spray foam in the crack!) and hope I can clean up the tray and reuse it if, It's not damaged.
but before I reset it, what should I do differently? should I be using wedi 320 tile adhesive to set the tray onto plywood (this is what they show on the wedi website), or use wedi 360 flexible cement?
Many thanks for your help folks, I'd supply beers if I could!!

kind regards
Pete

 

[Perfect Tiling]

Good morning Pete. Some plywoods out there these days aren't good at sticking to even when primed. I had a similar issue years ago and found out that the adhesive used to make the plywood (marine ply) was oil based....nothing sticks to oil. The tray should be ok to go again if you remove any excess adhesive from it.
I often overlay the floor with hardibacker cement board so you could put a 6mm layer 0ver the existing ply or remove a layer under tray and put down a layer of 12mm. However.....it may be that the adhesive has stuck to the plywood and not the tray as some trays have a coat of like chalk dust under them or are a fibreglass style that doesn't stick well to adhesive. Also, some trays say to bed down with a weal cement and sand mix.....this is so they sit level...not to stick them down so you need to see what tray instructions say.

You won't really know the problem until you get the tray up and see what the addy is stuck to....

 

[Dan]

Good morning Pete. Some plywoods out there these days aren't good at sticking to even when primed. I had a similar issue years ago and found out that the adhesive used to make the plywood (marine ply) was oil based....nothing sticks to oil. The tray should be ok to go again if you remove any excess adhesive from it.
I often overlay the floor with hardibacker cement board so you could put a 6mm layer 0ver the existing ply or remove a layer under tray and put down a layer of 12mm. However.....it may be that the adhesive has stuck to the plywood and not the tray as some trays have a coat of like chalk dust under them or are a fibreglass style that doesn't stick well to adhesive. Also, some trays say to bed down with a weal cement and sand mix.....this is so they sit level...not to stick them down so you need to see what tray instructions say.

You won't really know the problem until you get the tray up and see what the addy is stuck to....

Upgraded your account you now have access to the tilers forums arms. Mines a pint of guinnes.