Replacing shower tray (already) - advice needed

[motormad]

As part of my build, I fitted an acrylic shower tray. I built a frame to support the edges of the tray, then installed 50mm of PIR to support the drain pipes (internal). For the tray, I bonded 9mm marine ply to the underside of the tray to give support, then used 3mm underlay between the PIR and the ply to give good even coverage. This cracked after 4 uses where the tray floor met the tray upstand in an area that would not be stepped on.

The factory that made the tray was destroyed in a fire a year or so ago, and there are no stocks of the original tray. I found a company that make the same shape of tray (ish) in fibre glass, and ordered a replacement (5x the original cost). The floor of the tray is convex (lifting in the middle) by 16mm (measured on the underside against a straight edge corner to corner). I have challenged this, and the advise they gave is to use non-setting mastic to bond the tray to 6mm carpet underlay, and bond the underlay to the floor (or the PIR in my case) to both pull the tray into shape and to give flexible support thereafter.

I have not seen any information anywhere else about installing trays on underlay, so I am a little dubious about this method. However, I have already had one tray crack, and have no desire to have to strip the van back to this level ever again. Looking for views / advise / help please??

 

[SquirrellCook]

I suspect your GRP tray will fail in time too, it doesn't like being flexed. You can make semiflexible mouldings, but I doubt if many GRP companies will have experience of this.
Your soft support won't help.
Back filled with rigid expanding foam should help.

Mark

 

[motormad]

I suspect your GRP tray will fail in time too, it doesn't like being flexed.

This is my concern as well. I have not seen any information about anyone installing a shower tray on underlay. However, this is what the manufacturer recommends (challenged them 3x on this topic). If I install on a rigid base and it fails again, I have nowhere to go (albeit the GRP tray is significantly more durable than the acrylic one)

 

[SquirrellCook]

Like many production methods, profit is king.
If the acrylic was thicker, it would be more durable. Though slower and more expensive to mould.
Polypropylene would be best, though doesn't look as shinny. Also takes a very skilled vacuum former to work with anything over 2mm.
GRP, using woven fabric and epoxy gel coats would improve the product. Though expensive again.
Trevor's your grp man, I don't think much of his work has sunk!

Mark