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Community and Q&A

Closed-Cell Spray Foam vs. Mortar for Setting Bathtub

jmidway22 | Posted in General Questions on

We are setting two tubs in a remodel (Kohler acrylic drop in and an alcove). Typical install I would say just use mortar bed but always looking for a better method and so I am debating using closed cell spray foam. Seems it might form a better bed and also insulate and sound deaden.

I am seeing some anecdotal stories about its use and my plumber says they have had it specified on high end houses. Just wanted to see if anyone else had done this and if there were any tricks or things to look out for.

My understanding, you have to get it level first then fill it with water, then you can spray foam it, otherwise it might lift the tub instead of going out the sides.

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  1. Expert Member
    Michael Maines | | #1

    I've done both. If you use foam just be sure to fill the tub with water first, and go easy on how much foam you put down at once.

  2. Patrick_OSullivan | | #2

    Closed cell from a single part can or some two part kit?

    Either way, sounds super messy and annoying to do. If you have to fill the tub with water before you put the foam under it, it will be a pain to get to all the parts that need foam.

    Also, I would fear that anything that takes off spray foam overspray would also damage the acrylic tub.

    I have a Kohler acrylic tub and it's set in a mortar bed. Solid as a rock, quite literally, and I wouldn't do it any other way.

  3. jmidway22 | | #3

    Thanks for the input guys. I think I am going to shy away from the experiment and stick to the tried and true mortar bed. Kohler doesn't offer any technical paper or advice on it.

    Also one complication I realized was that my drop-in tub is not supposed to be supported at the lip (only the feet). So to use foam, I would have to manually level the feet, put weight or water in the tub then spray it. Seems a little easier to just set it in the mortar to level and bed it without.

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