Interior Wood Finishing
Whether it is a new piece of furniture you just completed or a new interior door you recently installed, you probably will want to apply some type of finish.
Why apply a finish?
The usual reasons for finishing interior wood are to provide some protection and to improve the appearance. A finish can make wood more stable, more resistant to abrasion, less prone to degradation by chemicals, and easier to keep clean. The natural beauty of attractive woods can be accented with an appropriate finish, while the appearance of woods with only modest grain and color can be substantially improved.
How should the suface be prepared?
Wood surfaces must be clean and smooth to achieve a superior interior finish. Carefully planed lumber must still be sanded or scraped to remove minor blemishes and to further smooth the surface before a finish is applied. Patching and filling minor crack and holes with wood putty may also be necessary.
What tools or equipment are needed?
Rags, brushes, pads, or spray guns can all be used to apply finishes. Cotton rags can be used for some finishing operations. Spray guns are perhaps the most efficient tool but are quite expensive and require a suitable work room. The most common tool used to apply finishes is a natural or synthetic bristle brush; throw-away foam brushes are also used. Match the type of brush with the finish you are applying. For example, natural bristle brushes may be preferred for solvent-base finishes, while synthetic bristle brushes may be selected for water-base finishes. High quality brushes are a good investment regardless of bristle type.
What types of interior finishes are available for wood?
Finishes used as topcoats or the final finish can be classified as film-forming or penetrating; film forming finishes can either be opaque (typically a paint) or transparent (including varnishes or lacquers). Film finishes typically protect better than penetrating finishes and offer more decorating alternatives. On the other hand, penetrating finishes may be easier to apply. Finishes should be selected that match the kind of wood and the performance requirements of the finished product.
What about preliminary operations such as staining or filling?
Before applying a transparent film forming finish, a stain is often applied to add color or accent the wood grain. Several types of stains are available, but oil-base stains are generally easier to use than water or solvent based stains for most amateur woodworkers. Large pored woods such as oak, ash, or elm may require a filler, if a very smooth surface is desired. The most common type of filler used is a linseed oil and varnish based paste wood filler. An alternative is to fill the surface using several coats of the finish itself, and carefully sand between coats to generate the desired smoothness.
What kind of finish is best?
Match the type of finish with the wood and, even more importantly, with the intended application. If the exposure requires a high level of durability and a transparent finish is desired, choices are fairly limited. If brush application is the only option, solvent-based polyurethane varnishes offer the most protection and durability although these varnishes may be more difficult to apply satisfactorily than other types. Lacquers are very easy to apply, cure very quickly, and are attractive; unfortunately this type of finish offers quite limited protection and durability. If spray equipment is available, other finishing options can be used.