National Coatings Blog

Can I Coat Metal Roofs?

How Do I Coat Metal Roofs?  

Coating metal roofs using the AcryShield Roof Maintenance System, ARM, is relatively easy.  But first, it is vitally important that the roof be evaluated for the type of metal and original coating used (if any).

If the roof is not coated, it is important to know the metal type.  If the roof is galvanized steel, aluminum, or Galvalume, the roof can easily be coated after a thorough pressure wash, rinse and drying.  Weathering of these metals causes a tough "scale" to develop on the surface which actually increases the adhesion of the coating to the metal.  Two coats of AcryShield roof coating are then applied.  AcryShield A500 or A510 is recommended for colder climates, while A400 is recommended for warmer more temperate climates. (See Metal Roof Membranes for more information.)

If the roof is steel and there is no "red rust" (iron oxide), then the roof can be coated as above.  However, if there is "red rust" present, this must be removed with a wire brush or wire wheel fitted to an electric drill.  After the rust is removed and wiped clean, RustShield A120 primer is immediately applied.  The RustShield primer contains a unique additive that prevents "flash rusting", discoloration of the coating due to the fresh steel's chemical reaction with the waterborne coating. 

If the metal had been previously coated, the roof is first cleaned as in the uncoated metal coating procedure above, and then coated with the AcryShield coatings.One key distinction: If the coating is Kynar or other PVDF coating chemistry, then AcryShield A130 normally recommended for coating PVC roofing is applied at 0.5 gallons/ SQ.  This acts as a primer to provide adequate adhesion of the AcryShield topcoat to the underlying coated metal.   

Details Seams and Penetrations:
After cleaning, details such as fasteners, penetrations, lap seams and standing seams are made watertight using butyl caps (applied to exposed fasteners) and butyl tape applied to lap and standing seams.  As an alternative, AcryFlex A150/151 and polyester mesh T272 can be applied to seams.

For additional information on metal roofing, download our FREE Metal Roofing Brochure and check out some of our Metal Roof Case Histories – U.S. Coast Guard Hangar at LAX, Hundley Hardware Co., GateGourmet, and Sears Warehouse.

To begin this article, we’d like to explain the term metal roof paint and metal roof coatings often referred to each other as the same. While this is fine with us, we will use the term metal roof coating because the word “coating” is the proper terminology as these products are thicker, more flexible and last longer than traditional paint. A paint could not provide the protection and durability a roof needs in order to survive the sun’s UV ray exposure, as well as, other harsh elements a roof endures throughout the year.

Now, back to the question – Do metal roof coatings reduce corrosion on my metal roof? YES! Coatings are excellent at reducing and inhibiting further rust from developing. The RustShield A120 is an excellent primer for metal roofs because it was specifically engineered to combat flash rusting and provide outstanding corrosion protection.

Next you are probably wondering how do you restore a metal roof that has rust corrosion? Well, on a typical aged metal roof, rust exists. In these areas, the rust must be removed either by cutting the sections of metal out that have rusted all the way through or by using a rust-inhibiting primer (RustShield A120) to stop the rust from spreading further. Butyl tape is then placed on all seams and screw penetrations and a polyester fabric is then embedded into the base coat at these areas to ensure a fully sealed and waterproof roof membrane. Lastly, an AcryShield acrylic topcoat with high reflectivity and durability is applied.  These topcoats can be color matched to your liking (see the picture below). Our topcoats provide excellent UV protection, longevity and are formulated for superior dirt pick-up resistance.

For additional information on metal roofing, download our FREE Metal Roofing Brochure and check out some of our Metal Roof Case Histories – U.S. Coast Guard Hangar at LAX, Hundley Hardware Co., GateGourmet, and Sears Warehouse.