Painting a weathered wood surface

Painting a weathered wood surface

By Amir Khan

Weathered wood can refer just as well to the exterior of a dilapidated old house or a wooden structure just completed awaiting painting. In fact, from a painting perspective, any type of bare wood that has been exposed to the weather elements for at least several weeks should be considered weathered wood.

Surface preparation

Meticulous surface preparation is essential when painting any surface and failure to do so compromises the appearance and durability of the finished paint job and eventually the quality of the wood.

Good surface preparation allows paint to form a tight, durable and protective bond with the wood substrate below. First, scrape off any loose or peeling paint while carefully inspecting the building’s exterior for damaged or rotting wood.

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Dry cot (dry, crumbly sections of wood) and wet rot (soggy soft spots) are caused by micro-organisms that thrive in damp conditions, just as mildew. All wood rot sections must be removed and the surrounding areas treated with a biocide designed for that purpose, before the hole is patched. If this is not done, the rot may continue to grow.

Small problem areas can be repaired with wood filler, but wood that is damaged beyond repair must be replaced before proceeding with the paint job.

Caulk/ sealer

Any knots or sap pockets in the replacement wood should be sealed to prevent resin bleed through. Since wood is susceptible to rot in excessively wet areas, further rot can be prevented by making sure the wood is protected against liquid water. To do so, caulk should be applied to inside and outside corners, joints, seams and other gaps where water could penetrate the woods.

The best sealer for this purpose is a top quality pure acrylic sealer. In addition to superior flexibility, these sealers, once fully cured, have excellent adhesive properties, which enable them to stick to a wide range of building materials, even under wet conditions. Acrylic sealers also have the advantage of being able to be easily over-coated with paint unlike silicon sealers.

Smooth and clean

Thoroughly sand and brush off all exposed wood surfaces to remove degraded wood fibres. When painting a rigid surface, such as weathered cedar, it may not be possible to reach all this damaged fibres with sandpaper.

In this case a wire brush can be used to remove as much of the deteriorated surface wood as possible. Any dust that remains should then be washed off by hand using a long handled brush and warm soapy water.

Work from top to the bottom of the wall then immediately and thoroughly rinse it before moving on to the next section. Although this method is time consuming, it is effective and low cost.

Treat mildew with a mild bleach solution of one part bleach to three parts water then rinse thoroughly.

Priming

Some woods contain tannins that can bleed through the paint, causing a brown stain on the surface. To prevent this apply a primer with top quality stain resistant acrylic latex or an oil based primer before applying the topcoat.

Paint selection

Use a top quality 100 per cent pure acrylic latex paint. These coatings are more durable than ordinary paints and have an excellent resistance to fading, peeling, blistering or cracking.

The writer works in the Technical Department, Special Effects, Basco Paints