Varnish is a clear glaze that is typically used to bring out the texture, color or grain in natural wood. It is also sometimes applied as a protectant over stained or painted wood. It should be applied in two to four thin coats and allowed to dry completely between coats for ultimate protection. The number of coats you apply depends on the item or object you are varnishing and its intended use. Varnishes dry slowly and must be lightly sanded between coats, which requires patience to achieve a flawless finish.
Most varnish manufacturers do not recommend using varnish on a painted surface. Use it over wood that has been stained. Stain soaks into the wood, leaving it unprotected against other discoloration that may be caused by oily fingers or water damage, for example. If you prefer a varnished trim over the painted trim in your home, it is best to remove the existing paint through stripping and sanding and then staining and varnishing the trim.
When painting trim, it is advisable to choose a semi- to high-gloss paint. The reasoning behind this is that trim in the home is usually located in high traffic areas, like door ways, and is more likely to get smudged and dirty. Glossy paints are not only durable, they also dry with a shellac or varnish-like finish that stands up to frequent cleaning to keep it looking its best. If painted in this way, varnish is unnecessary.
Due to its transparent nature, it is best to thoroughly clean the room in which you are applying varnish to the trim. This includes the trim itself, as well as the furniture and floors in the room. As an added precaution, lay down newspapers or tarp on the floor to keep any dust or dirt particles from getting into the varnish while it is drying. Wipe down the trim with a tack cloth before application. Tack cloths trap and hold dirt and dust and do a good job of preparing the surface for the varnish.
Another reason to avoid varnishing over light painted trim is varnish's tendency to yellow over time. Though it may appear clear at first, this yellowing will become very apparent if applied over white paint. Sometimes, it will take on a mixed color, such as if applied over a pale blue paint, and the resulting yellow discoloration can appear greenish. Keep this in mind when choosing trim color and finishing products.
Angela Baird has been writing professionally since 1995. She has a wide range of life experiences from work with abused animals with the Humane Society, to more than 20 years of hands-on experience in the culinary arts. In addition, she keeps horses and does her own home improvements and home gardening.