Replacing shower tray (already) - advice needed

motormad

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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??
 
Support for the floor part should if needed (why) be solid not underlay etc, this was mine.

1721741816109.jpeg
 
Thanks, I did have a browse through your pics and saw this. This is very similar to my first version other than I bonded the bottom sheet of wood to the tray. Still can't understand why if failed, but having un-done over a year of construction to rectify, I REALLY want to make sure this never fails again
 
If you put something soft under the tray it will flex and crack, you did, and it did, put it directly onto a spotlessly clean floor no adhesive or anything other than perhaps a tiny line of sealant around the very edge to stop any grit etc as it will work it's way under and through the floor as you bounce along the road.
 
A fibreglass tray will be a lot stronger than an acrylic on Kev.

16mm sounds a lot to me, to push/pull that down it has to go somewhere, it won’t shrink into itself. It will depend how many layers of matting they have used, if it’s thick it won’t be a problem unsupported but I suspect it will be thin. Can’t be sure without seeing it in the flesh but I would be rejecting it unless it’s around a quarter of an inch thickness or more
 
My meaning was all the support it needs should be a clean floor assuming it has a flat base.
 
nabsim said:
A fibreglass tray will be a lot stronger than an acrylic on Kev.

16mm sounds a lot to me, to push/pull that down it has to go somewhere, it won’t shrink into itself. It will depend how many layers of matting they have used, if it’s thick it won’t be a problem unsupported but I suspect it will be thin. Can’t be sure without seeing it in the flesh but I would be rejecting it unless it’s around a quarter of an inch thickness or more
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The fibreglass is 3.3mm thick (where I drilled out the drain holes), but certainly seems a lot stronger than the acrylic tray.
When I spoke to the supplier (3 times) about the shape of the tray, they gave me the impression I could take it or leave it, but they did not consider this a quality issue, and each time gave me the same instructions about bonding it to a carpet underlay, and bonding the underlay to the floor. When I suggested that the underlay may delaminate from the force of the tray, they stated that this would not be a problem...

My problem is that by the time this has been bonded down to this extent (and sealed against the wall cladding etc.) then this is never coming out again regardless of the shape of the floor.
 
The bottom of the tray should be reasonably flat or sloped towards the drain. It shouldn’t be ‘domed up’ in the centre by 16mm. If it was me I would be leaving it and getting money back unless you want to lay some more resin and mat on the underside to strengthen. At a quarter inch or so you can hit it with a hammer, it’s strong stuff.

A boat repair place should be able to make you one, if you have your old tray still they can make it the same as that.

In fact if there are any boat repair/fibreglass specialists near you take the new tray to them and ask their advice. It’s ok me saying something but if I actually had it in front of me it may be different to what I am imagining.

You can get a stainless one made to your spec as well
 
I have got to the stage where I am now committed to this tray (trimmed and drilled), so realistically I can send it back until I have fitted according to their guidance and it doesn't work. The other challenge is that to change tray design would probably mean destroying the rest of the bathroom to accommodate something different. Half of me is thinking better to strip everything out and start from scratch rather than reinstate now and have to rip everything out later, the other half is hoping that the manufacturer know what they are talking about, and the strength of the tray will support the movement they are recommending that it has
 
It's not inconceivable to make your own to fit the layout you need/want, make it in place.

Just watch a few videos to get your head around how to do a neat job.

 
motormad said:
I have got to the stage where I am now committed to this tray (trimmed and drilled), so realistically I can send it back until I have fitted according to their guidance and it doesn't work. The other challenge is that to change tray design would probably mean destroying the rest of the bathroom to accommodate something different. Half of me is thinking better to strip everything out and start from scratch rather than reinstate now and have to rip everything out later, the other half is hoping that the manufacturer know what they are talking about, and the strength of the tray will support the movement they are recommending that it has
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Can you put the underlay in position then put the tray in place then get in it and see what happens?
 
I don't understand why you would need underlay at all, it allows the tray to flex, and flexing enough will lead to cracks and leaks which will rot the underlay and the ply underneath it.
 
nabsim said:
Can you put the underlay in position then put the tray in place then get in it and see what happens?
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This is my next plan, albeit I will not be able to bond the tray down to counter the "bulge" - just waiting for the underlay to be delivered
 
motormad said:
Thanks for the suggestion, but this is definitely not the direction I wish to go in. I have tried using fibreglass before, and never achieved the finish that I desire
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It is easy to do but it's not easy to get a quality finish if you're not used to doing it, it was just a suggestion.
 
Pudsey Bear said:
I don't understand why you would need underlay at all, it allows the tray to flex, and flexing enough will lead to cracks and leaks which will rot the underlay and the ply underneath it.
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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)
 
Who is the manufacturer, do you have a link?
 
motormad said:
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)
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In my mind I am seeing that sponge like material, did they say what type of underlay? What I am imagining won’t allow it to bond flat so I must be thinking of the wrong stuff. Underlay will give cushioning between the base and the floor but not sure it can actually pull something flat bonded, not what I am thinking of anyway lol.

If you follow their instructions then you should have comeback if it doesn’t work if nothing else 👍
 
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