Timber windows – stain failure: peeling/flaking

Cause

UV deterioration of the timber surface beneath the coating

Repair

  • 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 or lightly pigmented coatings are vulnerable to ageing of the underlying timber and loss of coating adhesion under UV light from the sun

  • start the repair by removing all fittings and fastenings

  • scrape or sand off the existing coating to give an as-new timber surface. Remove all dust and ensure the timber is dry before starting to stain or paint the windows

  • recoating with the same type of product will restore appearance but frequent recoating will be required. Recoating of clear or pigmented film-forming stains is likely to be required every 6 months–2 years. Some timber producers do not recommend clear finishes for timber elements fully exposed to sun and weather

  • if painting the windows, prime the sanded timber with timber primer

  • fill holes and cracks with an exterior-grade timber filler and allow to harden, following the manufacturer’s instructions

  • sand any filled areas

  • prime sanded filler

  • paint with a minimum of two coats of enamel paint starting with the edges of the sash. Waterborne enamels that have lower volatile organic compound (VOC) levels than oil-based paint, and are quicker drying, are available.

  • major coating manufacturers have advice lines you can call for help and product recommendations for your specific circumstances.

Cause

Thermal expansion and contraction of the timber frame

Repair

  • Repair as above. Use a lighter colour coating that will be less prone to absorbing heat. 

Cause

Loss of adhesion due to excess moisture in the frame

Repair

  • Repair as above. Ensure the frame is thoroughly dry before coating.

Cause

Poor initial substrate preparation

Repair

  • Repair as above, ensuring that the existing coating is completely removed and the timber is clean and dry before coating.

Cause

The surface was damp or dirty when coated

Repair

  • Repair as above, ensuring that the timber is clean and dry before coating.

Cause

A dark finish was used 

Repair

  • Repair as above. Use a lighter colour coating that will be less prone to absorbing heat.

Cause

The coating was fully transparent (which gives no UV protection to the timber)

Repair

  • Repair as above. Some timber producers do not recommend clear finishes for timber elements fully exposed to sun and weather. Frequent recoating is likely to be necessary

Cause

Timber swelling/shrinkage caused by moisture absorption into timber end grain if joints were inadequately primed before installation

Repair

  • Repair as above, ensuring that the unit is completely dry before coating.