BJ Tanner replies: Sanding sealer is the first coat of finish and is the base for your top coats. Its purpose is to seal the pores of the wood while promoting adhesion and base for the finish coats. Sealer can be a purpose mixed solution or simply a diluted application of the same material as the top coat. Sealer coats are sometimes referred to as a spit coat due to its thinned application.
Shellac is also an excellent sealer that may be used under any finish. When using shellac I typically use between a half to one pound cut.
Sanding sealer is only applied as a base coat and should be lightly sanded after drying to remove any fuzz and minor finish imperfections. Use fine sandpaper, at least 200 grit, and do not sand through the sealer. If you do sand through the sealer, reapply sealer and lightly sand again. If the wood grain is coarse a second coat of sealer may be prudent. It should also be noted that sealer is applied after stain or dye. Sealer would prevent penetration of the stain or dye into the wood.
Eric Johnson replies: The best lacquer and sanding sealer that I have ever used is from C.E. Bradley. They are located in Brattleboro VT — 802-257-7971. I have found that you don’t need anymore than one coat of sanding sealer. Start out with one coat and when it’s dry you can sand it flat with 400 grit wet and dry sandpaper. Sand it dry and it will make a very fine powder. It is extremely easy to sand. Most time I don’t use a sanding sealer at all. I spay two thin coats of lacquer and then after a couple of hours I can sand it back and then next few coats goes on very nice. Hope this helps.
Gary Wood replies: As a general rule, the best sanding sealer would be the one that comes specifically with the brand of finish that you purchase. For instance, lacquers come in many different formulations and many brands will have a separate sanding sealer that is meant to complement their finish.
Dewaxed shellac is often considered to be a universal sanding sealer. If your favorite finish does not have a complementary sealer, dewaxed shellac is a good choice.
Another option that many finishers employ with good result is to use their selected finish and thin the first coat with the recommended solvent by about 25%. This provides good soaking into the grain before full bodied finish coats are applied. Soft film finishes like oils are generally meant for the “in the wood” look. Sanding a first coat of oil into the wood and wiping off the excess will seal the wood pores.
Sealers are manufactured for varying purposes, such as grain filling, flexibility for the topcoats and, of course, ease of sanding. Used alone, they might provide a quick build and an attractive finish in several coats, but this is seldom a good idea because they do not have the durability that topcoats provide. Because sealers are meant to be a foundation for the topcoats, it is best to use only one or two coats before top coating, and it is not a good plan to try to sandwich them between layers of topcoats.