The nature of wood and its reaction to water vapor and water, with particular reference to the British climate, are considered in depth. Other weather effects, such as sunlight, temperature changes, and wind are briefly reviewed. Basic requirements for protection of timber are considered from the point of view of design of joinery and the finishing system. Composition of the various timber finishes are discussed and advantages and disadvantages of aqueous versus solvent thinned systems considered. Results of flexibility and permeability measurements are reported and discussed in more detail.