Fitting shower tray to floor

21 Jun 2011
Reaction score
United Kingdom
I'm just about to install a quadrant shower tray directly onto the floor(access to trap available in cupboard directly below) which will be bonded to the WBP using mortar but wondered if I needed to prime/seal the WBP ply before laying the mortar or will the mortar bond to the ply ok?

Secondly, the shower trap has a large rubber seal that fits on the underside of the shower tray. Is it recommended to double seal with silicone sealant or will the rubber seal be good eneough?
Sponsored Links
I use powdered floor adhesive rather than cement, I know it says mortar but cement on wood just crumbles no mater what bonding or seals you use.
Silicon on seal can have adverse effect, it lubricates so if over tightened the seal can distort causing leak.
A wipe of silicon around the flange of the waste outlet above the tray may be of benefit, but, as above, silicon on the washer underneath can lubricate it enough to make it pop out as the joint is tightened.

The idea of using a weak mortar mix under the tray is to support it evenly on a cushion conforming exactly to the shape of the tray, keeping it clear of the flooring, which may, or may not be exactly true and flat. Bonding the bedding mortar to the flooring is not necessary or desirable, as the timber will swell and shrink with changes in humidity.

You could stick the tray down so it can't rock about on any small high spots in the flooring, but that can lead to it cracking as the timber swells or shrinks.

A full bed of plain sand would be enough to support the tray evenly, so it can't rock or move providing the floor is up to the job in the first place.
The cement is just there to stop the sand from trickling out around the edges.

Gravity usually does a pretty good job of holding a tray down, and the sealant around the edges is enough to stop it moving sideways.

with sand/cement mortar, and there's a chance of getting the tray out again without too much damage if you ever have to. Use flooring adhesive, and you are stuck with it - literally!
Sponsored Links
Thanks for the tips. I think I'll go with the mortar mix and then use sealant to secure it in the corner walls. I think the floor should be ok as it's 37mm thick now that I've overboarded it.

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local