It pays to look after exterior painted surfaces

Planning to wash your car this weekend? Great. But when did you last wash your biggest asset – your home?

You should wash your house each year to maintain the appearance of paint finishes and to remove any build up of salt deposits, bird droppings, mould and other contaminants that can interact with surface coatings. 

Salt-blown areas that are not washed by the rain need particular attention and if these areas require repainting, it needs to be undertaken after thoroughly washing and preparing the surfaces.

When maintenance becomes necessary

The time before a new paint system needs its first major maintenance depends on the condition of the surface prior to painting and the level of care that was taken during preparation. 

Be prepared to fix damage as it occurs, such as scrapes, hail damage or cracks. It's almost impossible to achieve a subtle finish in one spot over an existing system, so repair and prime the specific damage and repaint a wider area to get an even finish.

Outdoor exposure is harsh on paint

Protective coatings have standards that reduce the expected time to first maintenance from 15 years to 2 years depending on how exposed the site is to the elements!

Three elements that act at different rates on painted surfaces are sun, moisture and temperature differences. 

• Direct and reflected ultraviolet light degrades the binder and pigments of paint, resulting in chalking, erosion and colour loss. Lower quality paints will deteriorate faster. Acrylic paint generally resists the effects of direct light better than oil-based or alkyd paints because these paints absorb the ultraviolet radiation into the binder.
• Rain, snow, dew, condensation or sprinklers present various challenges to painted surfaces. Most coating systems allow some liquid or water vapour through. Timber can swell and shrink over time, so the paint fails due to movement on the surface.
• Heat can expand metal surfaces and impact wood as it drives off moisture content. To reduce the impact of temperature on surfaces, use light colours or paints that incorporate special pigments that reduce the absorption of heat.

To ensure the longevity of exterior paint that's exposed to extreme elements, make annual inspections and do running repairs to any areas that are damaged.

Good preparation is essential

The decisions you make when painting will influence what type of maintenance is needed and when it will be needed.

To get the best out of a paint system, focus on preparation. As a new paint film dries it puts pressure on the surface below. If the paint system is loose or powdery, movement can occur which affects the surface negatively.

Skimping on surface preparation can lead to many immediate issues or the early failure of a paint system due to underlying issues.

Here are some key things to be aware of when you're preparing a surface for repainting:

• Is there any moss or mould present? A quick wash with water will not remove spores or small particles – a chemical treatment is required. Moulds can regrow underneath new paint films popping them off the surface.
• Is the surface chalky or dirty? Proper cleaning involves both washing and rinsing. Cleaning solutions bind up dirt and small particles so they are washed away from the surface, rather than moved around.
• Are there old sealants and puttys? Failed sealants and puttys should be removed and replaced with new materials. Adhesion tests should be carried out on any previously painted areas.

Check with a reputable paint company or tradesperson to get the details on an appropriate adhesion test regime.

Use quality paint and follow the instructions

Start by selecting a quality paint specifically designed for exterior applications.

Making paint go a little further can have long-term impacts on the performance and time to first maintenance. Paint comes with a recommended spreading rate that is designed to ensure that when the paint has dried, there will be a film 25–35µm thick per coat. 

This is important as the final film thickness of a coating system is made up of the high and low points achieved during application. Paint that is thinned or over-spread will result in a thinner film coat. Even 10% thinning can result in a reduction of almost 30% in the dry film thickness.

Natural exposure studies with panels at a 45° angle show that one coat of paint can fail in less than a year. Using the recommended number of coats is critical to achieving long-term performance.

Ultimately, the more care and preparation invested at the start of the project, the better the outcome. 

Regular maintenance of exterior coatings will also ensure the system performs well and protects the building beneath.

Advice from Resene

Story by: Resene