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Thread: adding spray foam under installed tub

  1. #1
    DIY Junior Member ta240's Avatar
    Join Date
    Jul 2013
    Sacramento, CA

    Default adding spray foam under installed tub

    I was working in our one bathroom, which is very much torn apart, and can see through the wall to our other bathroom shower/tub and there isn't anything under the assembly other than the couple little feet supporting it. Since we are using that shower/tub now I've really noticed it flexing underneath me as I move around.

    I know I've seen on here were some manufactures say not to support their tubs and this one has no brand name on it. But I was wonder if it wouldn't be a bad idea and also if it is even possible to get spray foam under that one while I have some access to it.

    Has anyone ever extended the nozzle on a can of spray foam? I only have access to it from the end so the extension would need to be around 4' or 5' to get down the length of it. Can a small rigid tube be added to the end of the spray nozzle?


  2. #2
    In the trades Dana's Avatar
    Join Date
    Jan 2009


    It would take a heluva lot of cans to get there with can-foam.

    A 12 board foot FrothPak (or two or three) would have enough do something useful though. An inch of closed cell foam sprayed evenly over a fiberglass monocoque adds some structural rigidity, and 2" adds even more. To avoid stressing the tub you want to spray it in lifts of an inch or less. Too much expansion between the bottom of the tub and the subfloor could warp it or make it lumpy- the idea is to stiffen up the tub (and insulate it, which keeps the tub water warmer longer), not to support it on thin or uneven foam fulcrum point. The big box store home centers carry FrothPak kits- its' a 2- part 1.75lb density polyurethane, comes with a spraying gun and hoses,etc. It'll cover 12 square feet at 1" nominal thickness, and you can spray it from a couple feet back if you have to.

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