Waterproofing medium-density fiberboard (MDF) will protect the MDF board from becoming damaged and deformed when exposed to moisture. MDF is used as a cheaper alternative to wood in cabinets, furniture, baseboards and door trims. The only way to make the MDF board waterproof is to paint it. Painting the surface of the MDF board will make it resistant to moisture only if you use moisture-resistant paint, as this type of paint creates a more permanent waterproof layer on the MDF.
Insert the paint roller into the paint roller cover. Use a 3/8-inch roller cover to allow for better coverage of the paint on the MDF board. Place the roller tray liner into the roller tray.
Pour the latex primer into the roller tray. Apply the primer to the MDF, using the paint roller. Use a paintbrush to reach into any areas you couldn't paint with the paint roller. Let the primer dry for six hours.
Clean the paint utensils with water to remove the primer from the paint roller, roller covers and any other utensils you used. Prepare the utensils to paint again by placing the roller cover on the paint roller and putting a new layer of liner into the roller tray.
Paint the MDF with the moisture-resistant paint. Use a paintbrush to paint the edges of the MDF. Paint the rest of the MDF, using the paint roller. Let this layer of paint dry for four hours before applying another layer of paint. Let the final layer of paint dry for at least three days. Your MDF is now moisture-resistant and can be used near areas with high moisture.