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TOPIC: Painting/Coating metal roofs

paint types??

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I recently called a metal distributor that a friend uses in his metal roofing business. He offered a product that he says is better and it was cheaper than my other inqueries. He started getting into all the "Lingo" and started to lose me. What is G90 metal and Galvalume? He also said the paint system was Kynar 500. What is the difference between that and acrylic coated Galvalume? Thanks
Guest User

10/22/2002
Steel is coated with a Metalic coating to provide resistance to rust. The weight of the metailc coating is measured per sf . The minimum recommended for painted metal roof systems in Galvanized (ZINC) is designated as G90. The product recommended for uncoated roofs is Galvalume (45% Zinc/Aluminum) designated as AZ50. As the exposed Galvalume coating stains with processing machinery oil and even oils from handling, they now offer it with a clear acrylic treatment called Galvalume Plus which allows it to be rollformed oil free and be handled in the field without staining. The acrylic is designed to dissipate off the material within months leaving the natural hue of the Galvalume. One of the best pre paint finishes available is a PVDF based product made from Kynar/Hyplar resin which must include 70% resin to designated "500". Yes it is a top performer and typically comes wth a 30 year finish warranty. As to price, there are so many thichnesses and profiles that it is unfair to make comparrissons. You may be comparring apples and oranges. Look for standard colours and profiles which will keep the costs down. Hope this helps.
Allan Reid
Dura-Loc Roofing Systems, Inc.

10/22/2002
rustoleum makes oxidizing paints for rusting metal. Some say that other than a caustic power wash, no sanding is really necessary. I plan to wash, prime, and paint my standing seam roof myself. Is it advised to forget rustoleum products with anti oxidizing compounds and simply go with kynar resin based paints ?
Guest User

11/18/2002
You have a couple of different issues here. First it depends on the degree of rusting that you are experiencing on your roof. If it is a light surface rust thorough cleaning, drying, and a primer (rustoleum or others) designed to work over this should do an adequate job. If the roof is severely rusted more aggressive rust removal (i.e., mechanical removal) may be necessary as heavy rust presents an area where a more brittle type of rust has occurred. In any case, for maximum adhesion and corrosion protection it is recommended that you remove the rust to bare metal before priming. Kynar (if available in an air dry topcoat) would be used over the primer as with any good quality top coat material. Top coats should not be used directly on the bare metal, rusted, or severly weathered areas as adhesion could be a problem. There are some products that are intermediate and are consided Direct To Metal coatings that incorporate some aspects of primer and some aspects of top coat into one coating. Generally these are a compromise to the life and weatherabily in an exterior application and will have a shorter service life. A two step primer and top coat as you have suggested will offer better performance. Also, if you are using a caustic power wash, be sure to completely rinse the caustic from the surface after cleaning as this may react with the components of the primer. It would be good to discuss your issue with a local paint store for thier recommendation as to proper primer and top coats. Sherwin Williams, Duron, PPG, MAB, or others, deal with these issues regularly with their commercial paint contractors.
Guest User

1/8/2003