WHEN PAINT FAILS
The first signs of paint failure on timber are usually:
- At the corners of the board, because the coating has the least film build.
- At joints or mitres, because moisture has been absorbed into the end grain of the timber, swelling it and causing the paint to fail.
Other common failure modes and causes are:
- Blistering – caused by trapped moisture in the substrate, resin bleed in the timber or a heat source too close to the paint.
- Chalking – caused by UV weathering.
- Cracking – caused by recoating before the previous coat is dry, a hard coating applied over a soft elastic coating or movement in the material under the paint.
- Peeling, flaking – caused by an unsound surface, using the wrong paint for the substrate, using paint that is incompatible with the previous paint coating, leaving too long between coats, the surface is damp when painted, poor adhesion between coats, dark-coloured exterior paint applied over light or the paint coat is thinner where it is applied to the corner of the painted item.
To test how well a paint is adhering, make a number of criss-cross cuts (#) on the affected substrate with a sharp blade, then press adhesive tape over them. If paint flakes come off with the tape, the paint should be removed. If the paint failure is localised, repairs can be carried out by sanding and spot priming before the final coating.
- How long external paint will last depends on the:
- Quality of surface preparation
- Quality of the paint
- Amount of exposure to the sun– paint on the south side of a building will last longer than on the north or west side (providing its regularly washed and moss and lichen is prevented from growing as this to will damage the painted surface)
- Colour – lighter colours last longer than darker because they absorb less heat, so expand and contract less.
- Size and type of material under the paint – paint on wide timber boards won’t last as long as on narrow boards because the overall movement in wide boards is greater, and paint on cement-based materials (concrete, cement plaster, fibre-cement products) tends to last longer than paint on timber.
- Cleanliness of the painted surface – chemical clean often to remove airborne chemicals and dirt from the paint
- Number of coats applied
- Underlying colour – applying a dark colour directly over a light one can cause a previously sound paint to lose adhesion because of the higher surface temperature.
Paint will last better when the old paint is still in a reasonably sound condition when recoated.
Interior repainting is usually motivated by the need to change the appearance rather than replacing a failing paint. However, interior paint or clear finish failure is more likely in areas with a lot of moisture, such as the bathroom or kitchen. Another common problem is paint peeling off fibrous plaster surfaces. Moisture is absorbed into masonry internal walls can also cause paint failure.
As always, prevention is the best cure. What’s often overlooked is that if a paint coating is regularly maintained via an annual low-pressure chemical clean or moss treatment and the occasional sectional repaint or touch up is carried out your painted coating lifespan should be extended by 30%-80% and the other interesting thing is to maintain an average building with regular chemical washdowns and paint touch ups comes at a cost of approximately 5%-6% per year over the life of the coating.
If you repaint a timber cladding building in year 1 at a cost of $200,000
For the next 10 years, you clean and maintain the building every year at an average cost of $8500 per year
You have extended the life of your painted coating by 4-7 years at a cost of $85,000 saving you $115,000 which would have been the cost to repaint again after 7 years had you not maintained the building.
The best way to implement this type of saving is to develop a property care programme. A proactive reoccurring maintenance programme designed for your individual building and needs.