Natural finishes for exterior timber

Untreated timber exposed to the weather will discolour and degrade under the influence of physical and biological agencies. If the natural appearance of exposed timber is to be preserved, it is necessary to apply some form of surface treatment. This digest discusses the selection, use and maintenance of exterior wood stains, varnishes and other types of external natural finish. Before considering the different types of natural finish in detail, it first deals with the characteristics of the wood substrate that have a significant influence on their performance. The digest brings up to date the information contained in an earlier (now withdrawn) digest, No. 182.