stone resin shower tray help please

[bobber-job]

Hi - Im just fitting a 1600mm x 900mm stone resin shower tray and was wondering if I could get away without using mortar- the underside has a lot of ribs and I was thinking of using grip fill or similar just on the ribs- approx 5mm between bottom of ribs and plywood surface- using 4x2 timber and 18mm plywood. many thanks Mart

 

[flameport]

The purpose of using mortar is to fill any spaces under they tray so the whole thing is properly supported. Lines of adhesive will not do that.

It might be OK without the mortar. Or it could crack and be destroyed in a few weeks/months time, then it's buying a new tray and wrecking the tiling to fit it in there.
For the tiny cost of the mortar it isn't worth the risk.

If you haven't used or mixed mortar before, then just get a bag of ready mixed stuff which only needs water adding: http://www.wickes.co.uk/Blue-Circle-Quality-Assured-Mortar-Mix-20kg/p/153706

 

[chappers]

yep as above they are rarely perfectly flat or even

 

[bobber-job]

off to Wickes then ! - many thanks