Crazy idea - foaming a tub - thoughts?

[Mculik5]

Planning a bathroom reno and looking at tubs. We have a standard 60" x 30" alcove situation. Going to go with an acrylic tub - probably a Kohler Archer - so as not to have to deal with the weight of cast iron.

I'm a bit concerned about the strength/flexibility of acrylic and have also heard they don't hold heat well (important to me, as I have two young daughters who will be using this tub for the next several years).

Separately, I know most guys set tubs in mortar.

Thinking about all of this, I got an idea.

What if I built a form to enclose the open sides of the tub and then filled the underside of the tub with two-part, closed-cell foam (leaving room for the drain and overflow connections, of course)? Kind of like this - https://www.bertram31.com/proj/tips/foam.htm.

This would stiffen the tub, insulate it, and provide a planar surface to sit on the subfloor. And since the foam would expand up, it wouldn't deform the tub.

Based on my rough calcs, I'd need about $150 in foam, which isn't too bad. And since the foam would be pre-cured, I wouldn't be gluing the tub to the floor and making life miserable for the next guy (probably me in 20 years).

Thoughts? I'm posing this as a hypothetical at this point. Been thinking about it and decided I'd see what everyone else thinks.

Thanks.

 

[Jadnashua]

The mortar used to bed a tub doesn't typically stick. In fact, to make future replacement easier and to make it work better, you can put a sheet of plastic both under and over the piles of mortar. The mortar is there to help level the tub and to provide support so it doesn't deform from a point load when standing in it. That helps prevent stress fractures and increases the longevity of the tub.

Foam degrades over time. MIght work, might not.

 

[Sponsor]

 

[Terry]

I originally started using mortar to set tubs in when I had some issues with expanding foam pushing the bottom of a tub upward. It was an uncontrollable force that was deforming the bottoms of the tubs. Manufacturers started to build their tubs with more structure to prevent that from happening. The Archer by Kohler is a good tub. Still, the mortar set I developed has worked well for me and others. They have even included it in the instructions that come with the tubs.
They also make an expanding foam for insulating that is less expansive. Better just for insulating, and not for supporting.