Sanding and sealing MDF

Steps for sealing exposed core areas of medium-density fiberboard. 1998.

by Rick Hill

What are the recommended methods for sanding and sealing MDF?

The key is to fill the minute holes and lock down the fibers from further raising. We usually try to find MDF made for painting. It is more homogeneous than regular MDF and has less fiber raise on the routed cuts.

First finish sand with 150-180 grit silicone carbide paper. Blow off the substrate after sanding to eliminate dust. (Moisture content of the MDF should be stable at around 6-7%.)

Next, apply our very heavy solid White DuraSyn primer. Spray the routed areas first, let it dry for several minutes, than spray a wet coat over the whole part. Air dry 20-30 min. before sanding. The DuraSyn is a very heavy, high solid primer that was developed for MDF. It really fills the board well.

If it is a clear finish that's being applied, use polyurethane clear finish formulated for both MDF and Particle board.

After itís dry scuff with 220-280 grit stearated paper and then topcoat.

Rick Hill is an independent representative and consultant for industrial wood finishes. He has been involved in the woodworking industry for 12 years, and has been known to actually hold, shoot, and clean a spray gun.

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