Linx has had numerous inquiries regarding the painting of galvanized duct surfaces. To accurately respond to these inquiries, we have compiled extensive research on this topic.
Some of the most important points for your consideration are listed below:
- The use of a “paint grip” or “mill phosphatized” surface is not necessary to facilitate surface painting.
- Linx recommends using “DTM” (Direct to Metal) paint products. These paints are available through all major paint manufacturers and are specifically designed to adhere to galvanized steel surfaces.
- Regardless of what paints or surfaces are used, it is critical that all surfaces are cleaned of surface contaminants before applying paint. It is commonly recognized that today’s paints adhere equally well to a galvanized or “paint grip” surface, provided all surface contaminants, such as dust, dirt, mud, lubricant residue, etc., are removed before painting.
- Linx’s manufacturing incorporates water-soluble lubricants that leave little residue and can be easily removed before painting using a soapy water solution.
- All manufacturers use lubricants in their manufacturing processes to reduce the wear and tear on the manufacturing machinery caused by heat generated by friction between the machinery and the material’s surface. A ‘paint grip’ surface is rougher because it generates more heat than standard galvanized surfaces due to increased friction with the manufacturing machinery. Because of this, ‘paint grip’ materials require more lubricants, translating to more residue, which must be removed before painting to ensure paint adhesion.
- Most architects request a painted surface for an aesthetic appearance, desiring that the exposed ductwork in their buildings is attractive and free from unsightly surface blemishes. Linx Safe is a self-sealing duct system that eliminates the need for the installer to manually apply external sealants, tapes, and mastics, which are difficult to paint uniformly and deteriorate over time. If left unsealed, dust and dirt traveling through the air system (not removed by filters) will inevitably result in “air marks” around any unsealed joints, further detracting from the architect’s aesthetic intentions for the duct system.
Specification for galvanized sheet metal ductwork properly prepared for painting:
- Surface shall be clean, dry, and free from spiral manufacturer’s lubricants.
- Remove dirt and grease ductwork with water and a non-petroleum-based detergent (Simple Green, TSP, Krud Cutter, Dawn) and wipe dry with a clean cloth.
- Surface shall be free of foreign materials that will adversely affect adhesion or appearance of applied paint coating.
“DTM” (Direct to Metal) paint will adhere properly to galvanized metal. Sherwin Williams, a major manufacturer of DTM painting systems, recommends the following water-based painting system:
- Primer / Topcoat Sherwin Williams B42W series
- Primer / Topcoat Sherwin Williams B42T1
Other important information:
- When using oil-based paints, refer to the manufacturer’s recommendations for surface preparation and primer requirements. For instance, alkyd oils will react with zinc and saponify, leading to paint failure.
- Anecdotal comments from a major paint manufacturer implied that in their experience using paint grip, galvalume, and other similar surface treatments, paint failures have resulted due to the lack of adequate paint adhesion.
Our research will allow you to paint your exposed ductwork correctly during your next project. Happy painting!