Galvanised Metal Primer



The world would be a better place if all metal were galvanised (zinc coated), and galvanized metal primer was properly applied prior to painting. It this true? Probably not. But where galvanized metal is used, proper preparation of the metal surface is critical in order for the pain to adhere in the long run. Galvanized steel must be etched with a special primer in order for paint to achieve adhesion to the layer of zinc that coats the ferrous metal.



New galvanized metal that has not been painted typically has an oily film that helps the galvanized coating resist oxidation. Painting directly over this oil film with an alkyd/oil based paint can result in saponification between the oily coating and the alkyd binder. The paint will eventually start to peel and come off. The oily film needs to be removed with the proper solvent. Some primers or paints for galvanized metal that don't require a primer might allow painting directly over this oily film, so check on that.

Weather conditions vary across the US. In the Northwest, the climate varies between cool and wet in western Washington State to temperate and dry in eastern Washington State. The part of the state west of the Cascade mountains has a lot of cloud cover most of the year, and Oregon is even cloudier. But the temperatures do not hit extremes for either hot or cold. In Eastern Washington, nights can hit sub zero in the Winter, and 90's in the Summer. This is a great climate for growing apples, but houses with sheet metal roofs still need to be protected. In the cool moist and shaded environment, an aliphatic urethane has been recommended as a paint for sheet metal roofs.

IN the Southwest US, weather conditions are typically bright, sunny and hot. The conditions mean Summer days can reach well over 100 degrees with little humidity. Galvanized metal roofs are popular in this kind of climate. Sometimes they are not painted, but when they are, an acrylic urethane or a silicone alkyd coating is popular. Painting over galvanized metal can result in adhesion failure if the metal is not treated first. Treating is best attained with a primer that will self-etch the metal to achieve adhesion. Then, the final coat of paint is applied over the primer, resulting in a multi-layer coating that sticks, is durable, and offers color.

Metal Wall Shelves