Stain failure on stained or clear-finished timber weatherboards


Weathering, UV light exposure


  • The first step is determining (if not known) the type of finish. Is it:

    • a film-forming stain or clear finish, where the coating sits on the surface, or

    • a penetrating stain, where the coating soaks into the timber surface?

  • film-forming coatings weather by peeling or flaking or becoming more opaque while penetrating stains weather by losing their intensity and general appearance.

Film-forming clear finish or stain deterioration

  • film-forming clear or lightly pigmented coatings are vulnerable to ageing of the underlying timber and loss of coating adhesion under UV light from the sun
  • some timber producers do not recommend clear finishes for timber elements fully exposed to sun and weather
  • recoating of clear or pigmented film-forming stains is likely to be required every 6 months–2 years
  • scrape or sand off the existing coating to give an as-new timber surface. Recoating with the same type of product will restore appearance but frequent recoating will be required
  • major coating manufacturers have advice lines you can call for help and product recommendations for your specific circumstances.

Penetrating stain deterioration

  • wash the surface with a low-pressure chemical wash to remove dirt and any fungal growth. Do not waterblast as this will damage the timber. Once dry, apply a coat of penetrating stain following the manufacturer’s instructions 
  • penetrating stains will typically need to be reapplied every 2–4 years.