Wayne Parham Messages: 18786 Registered: January 2001
Illuminati (33rd Degree)
I'm not a woodworker, I'm an electronics man. So this is just what I've gleaned from the folks that do the work. I think it's good advice:
1. Seal edges with putty. Drywall mud is fine for this. You just don't want edges exposed because they're more porous than faces, and tend to swell. After the mud dries, sand smooth.
2. Use a solvent-based primer to seal the surface. That's lacquer, oil or alcohol. Don't use any water-based primer. Even a slight amount of humidity brings fibers to the surface, defeating the purpose. Standing water swells MDF and turns it into mush. After the primer dries, sand smooth.
3. After the primer is applied, you can use a water-based latex finish coat if you want, but it's probably best to use a solvent based finish coat like enamel or lacquer. Water is just not a good thing for MDF.