Photo by Roselyn Tirado

Originally Posted On: How to Paint Monolithic or Plaster Cladding (homesmart.co.nz)

Monolithic or ‘Plaster cladding’ systems rely heavily on paint as a key waterproofing component, so it’s important to get the painting right first time. Here’s what we know about painting plaster clad homes:

• When it’s time to re-paint the plaster cladding on your home, use a quality paint such as Resene X200 which uniquely combines low viscosity with high build ensuring excellent penetration into pores and superb adhesion. Not all paints are equal, other paints will not offer the same level of protection.
• Cracks in plaster cladding need to be ground out and repaired properly with an acrylic-based plaster. Don’t paint over a crack regardless about what it says on the tin about crack-bridging abilities. A large amount of our work is carrying out crack repairs and re-paints on houses that have only recently been painted by painters (or plaster repair companies!) who use crack fillers, cement based plaster or just paint straight over the cracks.
• Choose a paint colour with a Light Reflective Value (LRV) of 40% or higher. Lighter colours have higher LRV ratings because they reflect more sunlight and therefore absorb less heat. Darker coloured paints deteriorate more rapidly than lighter colours and can cause the plaster to crack as a result of the cladding heating up and flexing. Because of this, paint manufacturers will not guarantee their paint if the colour’s LRV rating is below 40% and is used on plaster.
• Applying the correct film thickness of paint is critical. Applying a paint too thin (or too thick) can cause problems like bubbling and flaking in the future. Paint that has been applied to thin offers less protection than a standard acrylic paint. Paint manufacturers provide technical data sheets which show the correct application rates of their paints.
  Keep the paint on your home clean with an annual wash. Paint lasts a lot longer if it is kept clean. This applies to all exterior house painting.
• Take photos to record the preparation work that is carried out on your home before the paint is applied. Paint manufacturer warranties can vary from two to ten years depending on the condition the substrate was in prior to the paint application. Proof of good preparation work and the condition of the cladding before the paint went on can help you if things do go wrong.
• Be aware that when your cladding is due for a re-paint, other cladding maintenance is likely to be due as well. As an example, all joinery to cladding junctions and cladding penetrations should be re-sealed at the same time as painting. This is because sealant has a similar life expectancy to paint. Missing or deteriorated sealant at these junctions is the number one cause of leaks on plaster-clad buildings. It might feel good to get stuck in and give the place a facelift, but plaster systems rely heavily on the outer coatings to keep the cladding watertight. Painting plaster cladding is a waterproofing process, not just a ’lick of paint’.