Timber that is unprotected and exposed to rain and sunlight will start to break down fairly quickly (depending on the species of timber). This deterioration will cause surface checking (cracking) due to the moisture change with in the timber. The timber will loose its natural colour and bleach down to various shades of grey spoiling the appearance. Dimensional changes in the timber resulting in changes in moisture content will have detrimental effects on exterior joinery, windows and doors, which for instance will swell and be difficult to open and close.
Exterior coatings are manufactured to stop this deterioration and maintain its dimensional stability, coloured coatings also maintain a desired appearance. We have products available in various forms from wood stains to wood paints and oils.
Also see our Exterior Wood Finishing Guide