Blistering of paint coatings to 1970s fibrocement wall cladding
While delamination to aged paint coats is common on timber weatherboards and roofing iron its is also seen on fibrocement surfaces.
The image above shows a house built in the 1970s and recently renovated with a modern exterior paint colour scheme to the fibrocement wall cladding. Large blisters appeared to the paint coatings over the following several months causing distress to both home owner and painting contractor. In this instance, the failure was between coatings applied many years before and were of a different colour to the latest paint coats applied. Full cleaning and preparation were carried out by the painting contractor prior to painting with 2 full coats of paint applied to the wall cladding.
Adhesion testing of the existing paint coating should be carried out by the cross-hatch adhesion testing method prior to any new coats of paint being applied.
Undoubtedly the dark colour has also contributed to the blistering in the photo image below. Where colours with low Light Reflectance Value (LRV) are to be used on aged fibrocement surfaces it would be best practice to advise the homeowners/ clients, in writing, of the heightened risk of possible problems with delamination that could arise.
All preparation and painting works should be in accordance with AS/NZS 2311:2017 Guide to the Painting of Buildings.
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