Hi all, I'm looking for some advice installing a stone resin tray.. Previously when I've installed these I've bedded them into tile addy on top of ply but they've always been the flat bottomed design. The tray I've installed on this occasion has a recessed/contoured bottom and it's on top of a timber platform topped with 18mm marine ply. I contacted the manufacturer (Simpsons) who stated that the tray would need to be bedded into a sand/cement screed. I asked if this needed to be a solid bed of a given depth, or spread using an adhesive trowel and I was informed that an 18mm trowel would be ideal. On Tuesday, I installed the tray using a wet mix (4:1), but I'm concerned that it's going to fail. Having installed the tray I put what was left of the cement on some scrap ply as I wanted to check how well it adhered and gained strength. The cement on the scrap ply when examined today is set but is not strong - there's no strength to it at all and it can be crushed back to sand with minimal effort. My concern is that the cement under the tray is in the same condition (weak and poorly adhered to the ply) so I'm considering relaying it. Question is, how should I do this given that I've followed the manufacturer's instructions already to this point? Thanks.