Varnish is applied either as a clear finish or as a topcoat finish over a stained-wood project. It is a traditional and durable finish. The process of applying varnish over bare wood or stained wood is the same. It involves careful preparation and attention to detail. The surface of the wood must be completely free of dust. Even the slightest bit of dust will show in the final coat of varnish. The door should be removed from its hinges and placed on a work surface for the most effective finish.
Remove the pins from the door, using a flat head screwdriver. Remove the hinges and other hardware. Set the hardware aside.
Go over the door lightly with 180-grit sandpaper, working with the grain of the wood. Do not sand through any stain or other treatment on the door.
Wipe the door down with a tack cloth to remove all dust.
Pour the varnish through a paint strainer and into a paint cup. Varnishes typically have sediments that must be removed prior to application.
Brush an even coat on the door with a varnish brush. Go with the grain of the wood. Allow the varnish to dry for 24 hours.
Sand the first coat on the door lightly with 180-grit sandpaper, going with the grain of the wood. Wipe the door down with a tack cloth.
Apply a second coat of varnish. Allow the varnish to dry for 72 hours.
Reattach the hinges and other hardware, using a screwdriver. Hold the door in place in the door opening. Line up the hinges and insert the pins in the hinges.
Thin, even coats of varnish will produce a more effective finish than one thick coat.
Wear eye protection when you're sanding wooden doors. Apply varnish in a well ventilated area.