How to Apply UV Protection Varnish on an Exterior Wood Door

Remove the door, if practical. Use a hammer and screwdriver to tap the hinge pins out of the hinges. Lay the door flat on saw horses and remove the rest of the door hardware. If it is not practical to remove the door, leave it slightly open while drying and tape plastic sheeting over the interior to keep bugs and weather out.

Clean the door with mild detergent and an abrasive sponge to remove grime and dirt. Allow it to dry.

Fill holes or gaps with exterior wood putty. Choose a color that best matches the existing color of the door, remembering that it will darken slightly after you apply the varnish.

Sand the door thoroughly with 180- or 220-grit sandpaper or a medium-fine sanding sponge. Sand in the direction of the wood grain until the entire surface is smooth and dull.

Remove sanding dust with a brush or vacuum, then wipe it down with a tack cloth. Tack cloths are sticky cloths, available at paint stores, which effectively remove fine dust from sanded surfaces.

Pour a little varnish into a clean bucket and apply it to the door with a natural-bristle 2- or 3-inch brush. Apply the varnish in a thin, even coat, working in the direction of the wood grain. Allow it to dry for the time recommended on the label, usually between eight and 12 hours.

Sand the first coat of dried varnish lightly and remove sanding dust with the tack cloth. Apply a second coat of varnish and allow it to dry completely before replacing the door hardware or rehanging the door.