We have bought a low profile solid shower tray. The bottom is completely fl at. Our other one had ridges and I installed successfully using mastic to s tick it to the flat ply floor.
I used the same technique on this one but think that because the bottom is flat the mastic wouldn't spread evenly and net result was some give in the tray. I have now lifted it up again and wonder what the best option is to f it it?
One option might be to put many thin beads of mastic with spacing to help t he spread but wonder if I will get the same issue. The manufacturer has an alternative of putting sand and cement on top of the ply and fit the tray o n top (unclear whether this is a dry or wet mix and what thickness)
Any advice appreciated.