Recently (since mid/late 2018) we have seen a surprising number of newly painted roofs where the paint coatings have blistered and peeled from the surface.
In all the cases seen recently, the roofs have much in common.
- They are approximately 20 years of age
- They were originally factory painted Colorsteel roofs
- Often, but not always, it is the first repaint of these roofs and they are only being painted as the original colour has faded or a change of colour is desired.
- The blistering is at the interface between the original primer and the bare galvanised iron
- Blistering was NOT noticed to the existing coatings prior to repainting
- The painting work has been carried out competently with pressure washing prior to painting, full coats of paint applied and quality roof paint products used
In all of the cases we have seen with roofing of this age where failure has occurred it is unlikely a failure of workmanship has contributed to the problem.
Adhesion testing of the roof coatings carried out often right next to the blistered area show the paint coatings are adhering to the previous paint coats. The blistering and delamination of the paint coatings is almost impossible to predict as can be seen by the adhesion testing noted.
Remediation of this work will be extremely difficult as the affected areas will need to be entirely stripped of the paint coatings, primed and repainted. It may be cost effective to replace individual sheets of roofing iron rather than strip the paint coatings.
NOTE: Extreme caution should be used when considering repainting roofs of this vintage. Painting contractors should make the likely hood of this problem known to the building owner when quoting work and tag all quotations that blistering of this nature cannot be foreseen. The painting contractor should also advise that they are not responsible should this blistering take place.
All preparation and painting works should be carried out in accordance with AS/NZS 2311:2017 Guide to the painting of buildings.
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