How to Sand Down Wood Fillers

A man works with wood filler.
What You'll Need
Screwdriver or knife
Wood filler
Putty knife
Sandpaper (coarse and fine grits)
Tack cloth
Paint thinner
Lint-free cloth
What You'll Need
Screwdriver or knife
Wood filler
Putty knife
Sandpaper (coarse and fine grits)
Tack cloth
Paint thinner
Lint-free cloth

Wood fillers have two jobs. The first is to fill holes such as dents, nail holes and cracks. The second job is to fill the pores of open-grained woods so that a stain can be applied evenly. Thicker fillers are for filling holes and don’t work well as grain fillers. Grain fillers are thinner, like batter. There are a few fillers that can do both jobs if thinned down to fill grain pores. For filling holes, many woodworkers use a filler made of nitrocellulose lacquer band and fine wood particles called wood flour.

Its advantages are that it is fast drying, has low shrinkage and comes in several versions to fit various woods. In order to sand down wood fillers perfectly, you must begin with the proper preparation of the wood and proper use of the wood filler. Once the wood filler is applied and sanded, it can be painted or stained.

Prepare the Void

If you have a hole in your wood that needs to be filled, first remove any debris with a small screwdriver or knife. Sand the edges of the cavity with sandpaper to smooth them out.

Test the Color Match

If you intend to stain the wood instead of paint it, you will want a close color match between the filler and the wood. You can mix your own wood filler to make a custom color match. Then make a test batch and put it into a small already stained area. Let it dry and then see whether it is a match. Even if you use a filler that is already colored, test the match before doing the whole project.

Apply Filler

Take the wood filler and put it into the cavity with the putty knife. Put in enough filler to overfill the hole. The excess will be sanded down to achieve a perfectly smooth surface.

Sand the Filler

It is extremely important to let the filler dry thoroughly before you begin to sand. Use coarser grit sandpaper to start the sanding. Sand thoroughly, using even pressure. As you get closer to the surface, change to fine-grit sandpaper. The goal is to sand the filler down flat with the surface of the wood and make it as indictable as possible. You want the smoothest surface possible so the finishing paint or sealant will not show the filler underneath.

Check the Surface

Check the surface to see if it is perfectly level by holding a flashlight at different angles to see if any filler is visible above the wood.

Clean the Wood

Use a tack cloth to wipe away the sanding grit and dust. Then use paint thinner on a lint-free cloth to wipe down the surface and give a final cleaning to the wood. Now, let the wood surface dry.

Wood Fillers FAQ

What should I sand wood filler with?

Sand wood filler down with medium-grit sandpaper and then go to a fine-grit sandpaper to get a smooth final finish.

The lower the number, the more coarse the sandpaper grit is. Ultra course sandpaper, for example, is between 12 and 40 grit.

Medium-grit sandpaper is between 100 to 200, generally speaking. Fine-grit sandpaper is between 220 and 320 grit.

Ultra fine sandpaper goes up to 1200 grit.

How do you smooth sand fillers?

Wait for sand filler to dry completely. Typically, this will take anywhere from three hours to three days, depending on the wood filler you are using.

Oil-based wood filler takes much longer to dry, around three days, while water-based fillers dry in just a few hours.

Either way, use medium-grit sandpaper to smooth down the filler after it has dried completely. When the surface area is smooth and even, sand again with fine-grit sandpaper to further smooth down the area.

What sandpaper to use to rub down filler?

Smooth wood filler down with medium-grit sandpaper in the 100 to 200-grit range. You can do this by hand or use a power sander to get the job done quickly.

Follow up with a fine-grit 220 sandpaper, using it by hand to completely smooth out the filled spot.

How long before filler can be sanded?

Depending on the type of wood filler that is used and how much, dry times vary greatly. Water-based wood filler dries more quickly than oil-based filler but the depth of the repair spot can also add hours of dry time to the equation.

When you have a very deep spot that has been filled or you're using oil-based wood filler, wait at least three days to allow for everything to dry. If you are using a water-based filler or you have filled a shallow spot, waiting about five hours should be enough dry time.

What is the difference between wood putty and wood filler?

Wood filler gets hard as it dries and it can be sanded down. Wood putty, on the other hand, does not.

Wood putty is called "plastic wood" because it will remain pliable and squishy for a long, long time.

Both wood putty and wood filler can be used to fill little cracks, dents, chips, and other imperfections in wood.