A friend gave me six untempered Masonite boards (thanks, Debra!) and I think I can use them for oil painting supports. I talked to several artists and they said that I needed to gesso the boards. So, I applied three layers of gesso to the boards with light sanding in between. They look so pretty.
But then, when I asked Celeste Bergin about it, she suggested that I paint a giant "X" across the back to prevent warping. So, I did it. Hey, if Celeste tells you to do something, you should probably do it because she's right most of the time!
Have you used untempered Masonite boards for oil painting supports? How did you prepare them?