Shower tray base

[Hawksley]

I'm about to refit my shower tray due to movement and leaks.

I have a new marine ply base with cement (wedi) board on top. I intend to use rapid set flexi tile adhesive to sit the shower tray on.

My question is; should I seal the cement board with an SBR primer or is that step not necessary?

 

[simplesteve]

There's 2 answers to your question:-
1. You don't need to SBR Cement Board : Rapid flex loves it and will adhere no problem. Give it a wipe with a slightly damp sponge first though.
( I would use a 6mm trowel for a very thin bed between the Ply and the cement board though, before you screw it down )

2. Another trane of thought is that the weakness here is in the rapidflex (not)adhering to the bottom of the tray. Most installers would simply forget about the C.Board, and just put on a good dollop of a sanitary silicone in rows and columns 6 inches apart.
This will 1. Definitely grab the board 2. Definitely grab the underside of the tray, and 3. Make it easier to level it once its lowered down. Obvs leave it for a minimum of overnight to cure before you stand in it.

 

[Hawksley]

There's 2 answers to your question:-
1. You don't need to SBR Cement Board : Rapid flex loves it and will adhere no problem. Give it a wipe with a slightly damp sponge first though.
( I would use a 6mm trowel for a very thin bed between the Ply and the cement board though, before you screw it down )

2. Another trane of thought is that the weakness here is in the rapidflex (not)adhering to the bottom of the tray. Most installers would simply forget about the C.Board, and just put on a good dollop of a sanitary silicone in rows and columns 6 inches apart.
This will 1. Definitely grab the board 2. Definitely grab the underside of the tray, and 3. Make it easier to level it once its lowered down. Obvs leave it for a minimum of overnight to cure before you stand in it.

Ok, that's interesting, thanks. Would sanitary silicone still work if the bottom of the tray is not level? It bulges slightly in the middle so rocks a bit.

 

[simplesteve]

Yes it would, that's the whole point of using it. Trays are never flat on the bottom.

 

[Hawksley]

Yes it would, that's the whole point of using it. Trays are never flat on the bottom.

ok, looks like I've been overthinking things.

 

[simplesteve]

Just make sure when you apply the silicone 'whirls ' that they're at least an inch high.