Prep for Painting Over Powder

Q. I came across a brief Q&A of yours on painting over powder coating dated April 2006 on www.pfonline.com. Our company is going through a corporate trade dress initiative that involves changing our exterior building colors. Currently, we have a number of locations that have powder coated window mullions that need to be changed in color. Is sanding the only method to get paint to adhere to powder coat, or can a good quality primer be used in lieu of sanding (provided there is no slip agent in the powder)? Obviously, what we want to avoid is paint blistering and peeling, which becomes an unsightly and continual maintenance issue. Are there specific types of primer and paint that you would recommend for this type of application? M.P.

A. I am glad you added “provided there is no slip agent in the powder” to your question about painting over powder coatings; it makes my answer simpler. Under those conditions, paint should adhere to the powder coating. The only need for sanding would be to remove any slip agents. After the powder is applied and cured, it is really a coat of paint. Therefore, you are re-painting over paint. When repainting, a primer is normally not needed. Depending on its composition (resin type) and condition, you may have to wash the powder to remove any loose chalk. If necessary, wash with an aqueous solution of a cleaner containing TSP (tetrasodium pyrophosphate). Rinse with clear water and dry before re-painting

The choice of type of paint to use depends on exposure conditions. Sincee you will be painting exterior surfaces, you must apply a weather-resistant coating. That said, the choice is yours.