shower tray mortar bedding

Large shower tray (1420x900x70) to fit. The documentation states it should be bedded on 5:1 mortar ensuring the base and walls fully supported. This is about 130kg of mortar (if it was a solid lump). Google searches have pulled up shower trays with adjustable feet or trays bedded on thin screeds and none about mortar beds 50mm+ thick.
Are there any pitfalls in this volume of mortar with chipboard floor and the fiberglass on the remaining surfaces? Any views/recommendations/tips e.g. lay polythene membrane over the chipboard, an off the wall suggestion "put the mortar in aluminium take away trays - crush down and easily placed"
Even sliding into place on removable battens is going to be a problem with 3 walls in situ and a mortar bed going from say 5mm at edges to around 50mm over the rest. If the top surface of the shower tray is 20mm thick would it be reasonable to assume that voids left by 3*2's pulled out after sliding the tray in on them would be insignificant (or in fact I'll need them to allow levelling of the tray) ?
Peterk

PeterK wrote:
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Seems a pretty thick layer... when I did mine I followed the instructions and am pretty sure it was not as deep as that. But I IIRC the bottom of the outer rim of my shower tray was level with the bottom of the main area of the tray so there was no disparity in the depth of the mortar - it was definitely uniform throughout, whereas it sounds like yours isn't?. Think the battens I used were something like 1.5" x 1", stood on edge, so the voids left when removing them were pretty trivial.
David

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It was a SHMBO purchase on offer in a shed. Best described as a "sink & drainer" tray. Just checked the supplied waste fitting and it looks like its centre lines up with the middle of the floor. I'm now very tempted to take 30mm off the skirt all round to avoid to 2 bends in first foot of waste pipe.
Peter K

PeterK wrote:
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I presume 5:1 here is the cement to sand ratio, and not the depth requirement.
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12 - 19mm of mortar would be more common for a shower tray.
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The usual base for a tray is 1/2" or 3/4" WBP ply. In a number of cases this needs to be raised a little above floor level to allow for pipework.
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I found a couple of bits of 15mm plastic pipe were usually adequate!

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How do you summise a 50mm+ bed of mortar. The mortar does not have to go up inside the void between the tray walls and tray sides, I think that is where your thinking is coming from, only the underneath of the tray base and the wall bottoms need to be supported. I have installed dozens of these things and always bed them on approx 1/2" thick. I use 1/2" square timber and space these out so I can 'float' the motar to a constant thickness and the after the tray is in slide the battens out. It can be tricky getting the tray into a three sided alcove but it can be done, with a helper if the tray is as big as yours!
Cross section of a typical tray ________ / _tray_ | / / X | | ---------/ / XX | | ----------/ XXXX | | YYYYYYYYYY | | YYYYYYYYYYYY
XXX area doesn't need mortar YYY area does
Hope that turns out OK after posting.
John

John wrote:
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Indeed, the only function is to make sure the tray doesn't rock around or shift..
I used up some surplus floor tile cement on mine