When we had acrylic shower units installed in our house apparently our employee did not know that they require concrete support under their floors. We learned about this the hard way when one of them broke with use, and we were obliged to replace it. We've used the others only infrequently since making this discovery.

Obviously it would be difficult to put concrete between an installed unit and subflooring now. Additionally, a warranty claim is not possible due the installer being under our employ (we paid him hourly), this problem is now ours to fix. Is there a product that could be used that would provide sufficient support? I assume we need something that would expand slightly to completely fill the gap with exerting too much pressure on the acrylic shower unit.

Thanks for your answers or suggestions!

  • 1
    What access do you have to add any material? Expanding foam could work, but how would you get it to where it needed to go?
    – JPhi1618
    Commented Jul 3, 2019 at 21:09
  • @JPhi1618: Thanks for responding. I can remove a strip of drywall from the base of the wall of an adjacent room. I was just looking around the 'net for possibilities and came upon the polyurethane foam that's used for supporting fence posts. Is that what you have in mind?
    – Bill Bell
    Commented Jul 3, 2019 at 21:14
  • Why can't you just go back to the contractor and seek warranty repair work? Depending on how long ago this occurred, this could be an option.
    – J Crosby
    Commented Jul 3, 2019 at 21:23
  • @JCrosby: Thank you. Please see my comment to J Raefield's answer. Put briefly, I need to solve this for myself.
    – Bill Bell
    Commented Jul 3, 2019 at 22:17
  • 1
    Pump mortar back in there via the removed drywall strip, using a grout bag. You could use bent cardboard to create "forms" to hold it till it firms up...? Commented Jul 4, 2019 at 3:41

1 Answer 1


The problem with expanding foam products is that you cannot effectively "control" the expansion, so it may expand in the gap to the point of damaging your acrylic from the other direction! The type that would be less likely to do that will also not really provide meaningful support; it will just compress with the flexing of the acrylic and you are back to square one.

I think a warranty claim against the installer is your best option. He did it wrong, he should make it right. He will not like it though because it will likely be impossible to remove the shower units without damaging them, they usually adhere them to the walls with construction adhesive.

  • Thank you. In most circumstances, you would likely be right. However, this work was done quite some time ago, and the individual I referred to as a 'plumber' was working for me on an hourly basis. This is my own headache to deal with. I take your point about what would be likely be expanding foam. I have no experience with it myself.
    – Bill Bell
    Commented Jul 3, 2019 at 22:15
  • 1
    Cans of expanding spray foam should be relatively safe if you use a little at a time. The danger is the foam needing to expand but having no where to go. Then it can reform the shower.
    – JPhi1618
    Commented Jul 3, 2019 at 23:29

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