Exterior Wood Maintenance - Exterior Guide - Page 6
The secret to low maintenance of exterior wood stain coatings is to monitor your exterior joinery, keep it clean and remove any moss, algae or any other contaminant that settles on the coating.
Exterior wood stains erode over a period of time and colour loss is gradual, maintenance will usually involve (after cleaning with soap and water) an application of a refresher top coat. A good quality wood stain should last about 3 years in south facing direction and longer in other directions.
Oiled finishes generally will not last as long as a stained finish, again depending on its exposed directional aspect. But close monitoring and a refresher coat is all that is needed when necessary.
Varnished coatings tend to become brittle and require the top coat to be removed by sanding and then a refresher top coat applied.
The consequences of neglected maintenance will undoubtedly cause the entire coating (top and base coat) to erode exposing the timber to the elements. Once exposed, moisture will penetrate the timber creating an unstable wet surface. Maintenance will then require the removal of all of the existing coating back to bare timber, sanding the surface again and then reapplying the base and top coat. Any attempt to spot treat any area will result in a very patchy appearance and lack of uniformity.