Q: The new galvanized ceiling in our warehouse has a shiny appearance and an oily feel. Will a latex or alkyd dryfall adhere to the galvanized?
A: In addition to standard galvanized steel, there are several other commercially available types of galvanized steel that you should be aware of including Galvalume®, Acrylume® and Acryzinc®. Surface preparation is the key to good adhesion on this surface; details regarding the appropriate cleaning of galvanized steel are available in the Sherwin-Williams Technical Bulletin, Successful Coating of Galvanized Steel.
Clean the galvanized ceiling per SSPC SP-1 Solvent Cleaning. This process includes steam cleaning, washing with hot soapy water, or wiping with solvents. All surface dirt, oil, grease and other residue must be removed.
Next test for presence of surface treatments such as chromates by dissolving 20 grams of copper sulfate into 1 liter of water. Drops of this solution are applied to test areas of the ceiling. If the galvanized turns black in 10-15 seconds the galvanized is clean and paint application can begin. If the surface does not change color the galvanized is treated or passivated with chemicals. At this point abrading or brush blasting per SSPC-SP7 is required for proper adhesion.
After the ceiling has been properly cleaned the latex dryfall may be applied direct to the galvanized in a one- or two-coat system. The alkyd dryfall may also be used only over an appropriate galvanized primer.
Q: Our client at the facility where I am painting wants me to coat the exterior of stainless steel piping. What system will offer adhesion to the pipe?
A: Proper surface preparation is the key to achieving good adhesion on stainless steel. First clean the pipe per SSPC-SP1 solvent cleaning. A water-soluble cleaner will remove grease, oil, dirt and other surface contaminants. Rinse thoroughly and allow the pipe to dry before primer application. Next apply a single coat of DTM Wash Primer at .7-1.3 mils dft. The primer will be ready to recoat in 2 hours when applied at 77 degrees F and 50 percent relative humidity.
DTM Wash Primer can be top-coated with a wide variety of finish coats including acrylics, epoxies, and urethanes to meet your customer’s requirements.