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We want to spray our basement ceiling rafters black. We also want to sound insulate using spray on foam between rafters.

boese | Posted in General Questions on

My question is can we paint the sprayed on insulation and will paint stick to it.

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  1. GBA Editor
    Martin Holladay | | #1

    Exposed spray foam is a fire hazard. Building codes require that you cover the spray foam with a layer of 1/2-inch drywall as a thermal barrier (for fire safety).

  2. Expert Member
    Dana Dorsett | | #2

    Spray foam is fairly mechanically rigid, and as long as the subfloor is already air tight it won't sound proof as well as fiber insulation.

    Similarly, fiber insulation that is dense-packed and mechanically pressing against the subfloor won't soundproof as well as low density stuff.

    Having the assembly air tight as possible (on both sides) is job-1 in the soundproofing biz, but mechanical decoupling is the next most important factor. If you're doing it with open cell foam for air tightness loosely install a kraft faced low density R11 or R19 against the subfloor (or just below the subfloor- giving it 1/2" of space with the kraft facer pointing down, and foam the facer with a 1-2" shot of open cell foam.

    But installing some furring strips below the batt (using UNfaced sound abatement batts, or cheap contractor roll
    R13s) and installing half-inch wallboard onto the furring using vibration absorbing adhesive (eg Green Glue tm) would provide more sound abatement than the spray foam for less money, and would be easy to paint black. If sound absorbing adhesive breaks the budget, (not that it's anywhere near as expensive as foam), air-sealing the edges of the gypsum with inexpensive acrylic painters caulk prior to painting will still make a measurable difference against un-caulked wallboard. Tape & mud the joints in the gypsum board using the conventional purpose-made materials.

  3. Stockwell | | #3

    Spray foam is not a good soundproofing material. As Dana said, it only helps in sealing gaps that may allow sound to pass. If you are not putting any drywall on the ceiling, save your money and put nothing between the rafters. It's a waste. Read up:

  4. Expert Member

    It will also look absolutely horrible.

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