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Q&A Forums Registered User
Posted: 1/02/2012 2:48 PM EST


Foam holding water, rusting metal substrate.
A friend of mine owns a large commercial metal building that he CC spray foamed in 2002-2004. The foamer put down 2-3 inches of foam and coated it with some kind of "moisture barrier paint." My friend tells me that all the steel girders and purlins under the foam are RUSTY. Bad rusty. The room in question had high humidity from some steam producing factory equipment. My friend's theory is that the moisture got through the paint and into the foam and then didn't have a way to dry out, causing the metal underneath to rust out.
When I want to help customers who have metal buildings with high humidity operations (like the last guy I talked to who had an egg-washing facility with the biggest washer system in production) then I want to know how to control their humidity and keep it out of the foam and off the metal.
Educate me guys. I'm struggling here.


Posted: 1/03/2012 8:39 AM EST


RE: Foam holding water, rusting metal substrate.
Ferrous metal must be treated before application of spray foam. Typically this includes sandblasting and priming with a rust inhibiting primer followed by a top coat. If the metal is already primed and coated then be sure rust has not set in. You can check this out by spot checking the metal by scrapping off the paint and looking at the metal.

If rust is on the metal, the foam will not stop the rust from continuing to spread. If there is no rust on the metal and the metal has been treated, there should be no problems with rust attacking the metal.

Rule of thumb when using spray foam on metal from the inside. When in a hot humid environment a vapor retarder coating over the foam will minimize the amount of water vapor transmitted through the foam and reduce the potential for condensation against the metal/foam interface. But if there is moderate temperatures and humidity within the building, then the vapor drive goes in both directions such as is typical with most buildings then you would not use a vapor retarder coating over the foam.

In this case, I assume the inside temperature and humidity would be higher than the outside a large majority of the time, so a vapor retarder coatings would be in order. The coating should be installed uniformly to the correct thickness without holidays.

Check out SPFA's technical guidelines AY 103 Insulating Outdoor Service Vessels and AY 134 Insulating Metal Buildings with SPF and AY 118, Moisture Vapor Transmission Paper for more detailed information and instructions.


Q&A Forums Registered User
Posted: 1/03/2012 5:52 PM EST


RE: Foam holding water, rusting metal substrate.
Thanks Mason!

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