How to Clean Galvanized Steel Before Painting

Question:

I need to clean galvanized steel mir- ror bases prior to painting. We can’t remove the galvanization. Any suggestions? Thanks. T.M.

Answer:

Most aqueous, alkaline cleaners will attack and remove at least some of the galvanized coating unless it is a near-neutral cleaner or contains silicates that will prevent most base metal attack. Mini-mizing time, temperature and concentration will also minimize galvanized coating removal.

Solvent-based cleaners will remove grease, oils and particulate without attacking the galvanized surface. Something as simple as mineral spirits may work adequately. Although, if more difficult grease and oil removal is necessary, a chlorinated solvent may be required. While it does not seem to be politically correct to talk about solvent cleaning, there are still people making this type of chemistry and equipment. I would suggest starting with a cleaner supplier first, then matching their cleaner with the proper equipment. You can start your search at PFonline, www.pfonline.com, in the suppliers directory or in the 2000 Products Finishing Directory and Technology Guide under Solvent Cleaners, CFC-free and Solvents, degreasing on pages 567-569. Equipment sources can be found under Degreaser, solvent, vapor, on page 410, although I would expect that they would do more than just vapor degreasing solvent systems.