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Home > FinishingHow to choose the right finish, Part 3Now let's look at protection and durability of finishes.Protection: Most wood looks nice completely unfinished. So why do we even bother to go through all the steps necessary to finish a piece of furniture? Two reasons are: To protect the wood and add to it's durability. The best reason to protect wood is to slow down the water transfer between the wood and it's environment. Wood movement is caused by moisture transfer. When wood has a high moisture content it swells, mostly across the grain. The opposite is true when wood loses moisture. This movement can play havoc on glue joints. For a finish to be resistant to water and water vapor a finish must be fairly thick. The best finishes to use for this are varnishes and water based (there are others but they must be sprayed on). Shellac does a good job against water vapor but a poor job against direct water contact. Wax and oil finishes do the poorest job against water and water vapor mostly due to their thin coats. No finish will completely stop the transfer of moisture between wood and it's environment, some just do a better job of slowing it down. Durability: The durability of a finish must take into consideration wear resistance, solvent and other chemical resistance, and heat resistance. Varnish and water base finishes do a good job with wear resistance. Shellac and brushed on lacquer do a fair job. For finishes that can be applied by hand, varnish is the only one that gives good chemical and heat resistance. In our next article we'll look at ease of application, health concerns and ease of repairing. Craig Stevens Woodworkers Resource |
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