Carbon steel sheet is called “galvanized” when coated with a thin layer of pure zinc. Galvanized metal must be thoroughly sanded to give the epdm some “teeth” to grip into otherwise the product will lose adhesion. Regarding galvalume roofs have a clear protective coating applied to it and the Liquid Butyl Rubber will not adhere. One was to determine this is to scratch surface--- if no zinc comes off then a clear coat exists and the Liquid Butyl Rubber cannot be used. If areas show some rust corrosion that is an indication of the absence of a clear coat and the Liquid Butyl Rubber would work.
Liquid Butyl Rubber will not work on Galvalume. Depending on the age of the roof you may be able to scratch the metal and see if a clear coating comes off or not. Galvalume-coated steel will be less likely to rust than normal galvanized steel.
