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.
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.