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Site mixed sand/cement mortar has only poor cohesive strength: it will shrink and crack.
Dual shrinkage compensated grouts are available. -
Found the pics of when I did mine of a similar size - frame under marine ply, then weak sand/cement mix to support the tray.
Having a friend help out was invaluable.!
mespilus
Dramatic_Hammer
@BrickMan
Ok 1st time installing a MASSIVE shower tray. 1400 x 900mm. Biggest I've done before was maybe 1100 x 700.
Its ABS resin stone (concrete with a ABS cap on it) weighs 40-50 kg.
Going to be raised above floor due to joist and waste constraints.
MFTR seems to suggest consolidate the floor, so big sheet of ply, screw it all together, 12x of their big plastic feet in the correct locations stuck to underside of tray. Plonk it down, make level. Done?
I'm a little skeptical. 3/4" ply onto old school near 1" thick pine boards that are already screwed to joists that haven't moved or made any movements in decades is a very solid base already, much better than a new build chipboard job. However its the 12 plastic feet, they are of good quality and seem to be enough, I can stand on one and it won't deform. But its over time, something is going to move and cracks will happen.
My method... terrible drawing attached.
Tray
Sand cement (weaker mix, more for support than anything as underside of tray is not like glass) 10mm approx.
3/4" ply
12x plastic feet in right locations under the ply, screwed to it,
3/4" ply, screwed to feet above, and floor/into joists below.
Some kind of trim to cover the 85mm-95mm void at front of tray.
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