Bonderized/paint grip steel
Bonderized steel is a Galvanized G90 that has been put through a phosphate bath and has a layer of Chromate applied to it and then dried, leaving it ready to accept paint. The process produces a dull gray colored finish.
Bonderized steel is commonly referred to as Paint Grip steel. Paint Grip Steel is meant to be painted as it holds paint very well. Typical uses are for rain gutters, downspouts, roof flashings, and roof valleys. In recent years, architects have used Bonderized steel for roofing and siding without applying paint to the steel. This is done to achieve a beautiful dull gray weathered look.
There are some things to be cautious of when using Bonderized steel for metal roofing and siding:
Bonderized steel is not a warrantied product.
Bonderized steel can range in color from an almost black color to a light powdered gray. There is no guarantee that one shipment of Bonderized steel will look like the next. If repairs are done after an initial installation available coils are likely to be of varied colors that will not match the original material.
Bonderized steel has scratches on it that occur during the processing and manufacturing cycle as well as during installation. This product is meant to be painted. Bonderized steel may turn a dull gray and scratches may be less apparent after installation due to exposure to the environment. This is the weathered appearance that makes this material an attractive product.
Bonderized steel may develop white rust. A prolonged period of wet and humid weather during the construction period may create conditions that promote white rusting. White rust does not indicate serious degradation of the zinc coating nor does it necessarily imply any likely reduction in the expected life of the product.