Advice for applying external coatings

Weather Conditions and Moisture Content

As we live in a temperate environment there will be time when it is not appropriate to apply a coating to timber products in an external situation. Coatings should not be applied in wet conditions or when rain may fall before a coating has time to fully dry and cure. Furthermore, timber must never be coated when damp. The ideal moisture content for timber is around 14%, higher than this and you run the risk of the moisture preventing good adhesion of the coating and causing the coating to flake off as it tries to evaporate out of the timber.

Ambient Temperature

The temperature at which the coating is applied must be considered, no coating can be applied when temperatures are at or below 5°C, or where temperatures may fall below this before the coating has fully cured. Some coatings must not be applied in temperatures below 10°C; otherwise the chemical reaction required for the resins to cure will not take place.

Pre-protection of timber

If you are faced with the prospect of not being able to protect your timber with a coating due to conditions the following advice may be useful.

As soon as possible timber should be protected with a clear, water repellent timber preservative. This may be applied in temperatures above 0°C, but the timber must be dry. This will provide some protection against the onset of wood disfiguring fungi such as blue stain and will help prevent excessive movement of the timber due to an increase in moisture content. Some change in the surface colour of timber will be noticed over time due to the generation used slow grown hardwoods which are naturally durable but are becoming scarce and can come from unethical sources.

Softwood timber will last for many decades but must be protected from the elements: sunlight causes timber to degrade via the action of the UV light and wet weather will increase the moisture content of the timber to a point where it can become susceptible to wood disfiguring and destroying fungi. The following information is designed to give you the background knowledge to protect your new investment.

Protecting against fungal attack

As soon as your new timber building is erected it should be treated with a clear preservative to give long term protection.

The preservative should be applied at the specified rate, which may mean giving it a couple of coats. The preservative should be allowed to fully dry before applying final protective and decorative coating. The time for the preservative to dry will obviously depend on the time of the year and should always be a minimum of 48 hours.

Once the timber preservative has dried apply at least two coats of a preservative coating such as Sovereign SX70. It is important that no areas of timber are left bare and particular care is taken at end-grains to ensure they are fully sealed.

Effects of sunlight and such areas should be rubbed back to bright wood before further coatings are applied.

As soon as conditions are suitable then proceed with fully protecting the timber with SX70, ensuring that the timber is clean and dry.

Preparation

Prepare timber by sanding as required, making sure no sharp edges are present as these result in a thin coating and can lead to premature failure. Any fungal growths should be treated with a fungicidal wash and allowed to dry. Knots with any resin exuding should be scrapped off and clean with methylated spirits. Knots may continue to bleed for a couple of years and this should be allowed to occur, removing the resins as necessary from the coating.

It is false economy to purchase cheap paint brushes; they give a poor quality coating, loose bristles and generally do not last. It is wise to spend some extra money on a high quality wood stain brush as this will give your wooden gate a superior finish and remember brushes can easily cleaned and reused.

Preventive care and maintenance

All coating should be inspected on a yearly basis to ensure their integrity is intact and repairs made as required, perhaps more often if environmental factors dictate i.e. if exposed to extremes in temperature or exposed to prevailing weather conditions.

Generally speaking a quality coating such as Sovereign SX70 will last in excess of 3 years, however it is still wise to check as the coating could be accidentally damaged through knocks and abrasion.

When it does become time to re-apply a wood stain then the best method is to check for any bare areas of timber and rub these back to bright wood. These areas should have another coat of preservative applied. The remaining areas should be cleaned down with detergent and water before being rinsed and allowed to dry. Once dry simply apply a further coat of wood stain.