How to Varnish Large Knots in a Door

Knot Integrity

• Pine, alder, fir and birch are all known for large, aesthetically pleasing knots. Other hardwood species have small knots but nothing to the degree that might differentiate door finishing techniques from a standard door. When finishing doors with large knots, always check the integrity of the knot before finishing. Tight knots are incorporated into the grain, seamlessly filling the wood without any visible pits, cracks or separations. Loose knots are just as the name implies: loose. Tap on the knot with the end of a putty knife. If the knot is visibly loose or it twists, rattles and rolls, add glue to secure it. Place masking tape around the knot and force glue into it until it's saturated. If the knot falls out and can't be glued back in, cut a matching piece of wood from a dowel rod, file it to fit, add glue and tap it into the hole. Use clamps if necessary. Sand and finish it as you would with any wood.

Prep

• Fix the small defects after determining that the knot is tight and will not fall out. Begin by adding wood putty to the knot, even if it seems flat and tight. It's a routine to force wood putty into the knots before finishing to fill hairline cracks, splits or other defects that you might not notice. Scoop out a generous amount of wood putty on a putty knife. Smash and drag the putty across the knot with force to create a smear. Flatten the putty deep into the knot. It might not look as if the knot is absorbing the putty, but smaller particles enter where needed to fill and smooth the surface of the knot. Allow the putty smear to dry for at least 30 minutes. Sand the dried putty off the knot with short strokes parallel with the grain using 100-grit sandpaper. Repeat sanding with 180-grit sandpaper. To ensure that the door finishes evenly, sand the entire surface of the door if possible. If you're only finishing the knot, tape it off using masking tape and focus on the knot only.

Stain

• It's not necessary to stain knots. They're already dark and stand out, but you can add stain if you'd like to get the knot to take on a reddish tint, black walnut, fruitwood or pecan tint, among others. Stain adds tone to the knot, and stain will have no effect on the final varnish finish. After sanding, applying stain and allowing it to dry, varnish can then be added. It's best to finish the entire door when finishing knots, but if desired, you can place masking tape around the perimeter of the knot to isolate it, and focus the varnishing on it alone. Spray a light, wet coat of aerosol varnish on the knot or door surface. Hold the can 8 inches from the surface, tilted at 30 degrees. Spray overlapping bands of varnish across the door or knot. Allow the varnish to dry overnight, or according to the manufacturer's directions. Varnish dries at different rates according to weather, humidity and application methods. It should be dry to the touch, not tacky.

Sand

• Sand the knot, or the entire door, by hand using a hand block with 180-grit sandpaper once the first varnish coat is dry. Sand lightly until the dry varnish produces a light, powdery coat on the knot or door. Don't wipe the dust off, it aids in curing subsequent coats of varnish. When you're finished sanding, spray another coat of varnish on the door just as you did the first coat. Allow the varnish to dry overnight. Two coats of varnish is sufficient to seal and protect the knots in the door. Use up to four coats for a thicker, heavier gloss.