I'm going to install a new quadrant shower tray (900x900mm) in our re-fitted ensuite bathroom. Being made of stone resin (acrylic coated) tray is ***king heavy and is going down on standard t&g floorboards (upstairs room).
Instructions say to lay it down on a sheet of marine ply and bed onto a sand/cement mix. Presumably this is to insure a firm and even base. Anyone any experience of doing this? How thick would the ply have to be, and what ratio of sand/cement should I use? Would this be sufficient to hold it in place?
I have got really heavy marble slate tiles on the floor and walls. Each tile is about 60cm x 30cm and 1cm thick and must weigh 20kg and there are dozens of them. This lot must weigh a tonne at least. I bought the house with the en suite and bathroom done like this and have the receipts from the previous owener of the house that it cost near on £25 grand to have done. I was worried by the weight of this stuff upstairs but there are no cracks or anything in the downstairs ceilings. It's been like this for two years so I'll keep you posted !!
Don't worry about it. The size of the tiles doesn't matter, only the thickness and most bathrooms these days have a good 1cm of stone or ceramic cladding their every surface. A tonne really isn't that much to a well built house, especially spread out on largely load bearing walls.
I did a similar job a few years ago and the method I used was thus:
1 Laid, levelled and screwed a piece of 20mm (3/4") WBP plywood onto the floor the size of the base.
2 Cut three strips of 25mm x 13mm (1" x 1/2") ply wider than the newly laid board and laid them one close to each end and on in the centre on top of the same (adjust the quantity and spacing to suit your job as needed).
3 Mixed a dry mix of sand and cement to the following ratio 3 sand, 1 cement with just enough water to bind it when squeezed in the hand.
4 Laid and levelled the above between the pieces of previously cut strips of plywood and used these to 'screed' to level a finish to the sand/cement mix - and then left them insitu for the following operation.
5 Place the shower base gently on top of the sand/cement and plywood strips, adjust the base to where it has to go, gently remove the ply strips by pulling them out one at a time, give the shower base a little twist back-and-fore to settle it in place and then leave the sand/cement to set. Don't bother trying to fill the gaps left by the strips as they will not affect the strength of the work.
Remember, that this base has virtuall no adhesion and it will be possible to move the shower base if it is carelessly handled or kicked after the compo base has set and before tiling or joint sealing.
AIUI, the boiling actually refers to localised boil spots that occur when damp plywood is in direct sunlight. Non WBP ply can't resist such spots, causing delamination. I may be wrong, but that was my understanding.
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