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Community and Q&A

Prepping a Metal Roof for Spray Foam

HLCC | Posted in General Questions on

How do I prep the tin roof on my barn before using spray foam (closed Cell)  does it need to be washed and dried, or do I need to use a cleaning agent of some sort. This barn is about 16 years old and the underside of the roof is smoked up, and dirty.      Thanks in advance   Joel Halfmann

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Replies

  1. Expert Member
    Akos | | #1

    Joel,

    Polyurethane spray foam is the stickiest material I've worked with. It seems to adhere to everything, the hard part is keeping it off building surfaces.

    If you want to be sure, you can buy one of the small 15 board foot two part spray foam kits and try it on a section of your roof.

    Usual problems with adhesion comes when applied to either a too cold or wet surface.

  2. Expert Member
    BILL WICHERS | | #2

    I agree with Akos about the stickiness of spray foam. I got some "spray foam mist" on some of my extension cords and the case of a wire puller years ago, and it's still there, and I cannot get it off no matter what I try to do. We may call it "insulation", but it sure seems to think of itself as an adhesive! :-)

    You just need to clear off any loose debris or oil films. You don't need the surface to be as clean as you would if you were painting. What you don't want are cobwebs, anything that will flake off or seperate over larger areas (a little spot here or there isn't usually a problem), stuff like that. Oil films do mess up adhesion, and excessive moisture content is a problem for that too. Things that flake off will let go when the spray foam hits, and can sometimes result in voids or "dropped" lifts of spray foam in severe cases. Things like cobwebs get compressed into a sort of paper that interferes with the spray foam adhering to the substrate in that area in the cobwebs are thick enough.

    Brushing with a broom to clear loose debris will usually be enough, and you often won't even need to do that. I would at least do some spot checks for things like thick cobwebs or surfaces that might peel or seperate when small amounts of force are applied though.

    Bill

  3. krom | | #3

    I would put up fabric, cardboard, or cut and fit sheets of thin rigid foam, incase you ever need to take off or replace a sheet of tin in the future.

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