Q. In all the years Ive painted in oils, Ive always been told to use untempered Masonite because the oil mixed into tempered Masonite made it unsuitable for use in my medium. Is this still true?
A. In the past, it was true that Masonites tempered boards were to be avoided because of the oily addition that was included to make them harder and water-resistant. Today, however, a completely polymerized resin is used to temper the boards in place of the oil—which makes it less reactive with art materials.
Even with this change in the composition of tempered board, youll still have a problem getting coatings of oil paint to stick to its surface. I used to recommend lightly sanding the surface of the board to provide some tooth for adhering a painting ground. But during a recent conversation with a retired paint maker, he discouraged this practice because sanding opens the grain of the board, making it susceptible to warping. He suggests—and I now recommend as well—wiping the sides and edges of the board with an alcohol-dampened rag to remove any residual grease, and then allowing the board to dry overnight before applying size and ground. You can use rubbing alcohol (70 percent isopropyl alcohol) from your local pharmacy for this task, but be cautious about inhaling the vapors and be aware that alcohol can be a fire hazard. Then size the board with a PVA size (such as Goldens GAC 100 medium or Gamblins PVA Size) before applying at least four coats of an acrylic dispersion ground.
Mark Gottsegen is an associate professor of art at the University of North Carolina at Greensboro and chair of ASTM Internationals subcommittee on artists materials.