Paint and finish defects in Australian residential builds

What it is

Painting on a residential build is a finishing trade but the failure mode is almost always upstream. A paint defect is rarely a paint problem on its own. It is a substrate problem, a preparation problem or a sequencing problem that the paint film makes visible. AS 2311, Guide to the painting of buildings, sets out the surface preparation, primer and topcoat selection, application conditions and re-coat intervals that a residential paint system has to meet. When the standard is skipped, the defects appear within months.

Substrate preparation

AS 2311 puts the heaviest weight on substrate preparation. For new plasterboard the surface has to be dry, dust-free and stopped with a sealer or undercoat designed for the topcoat. On timber the moisture content has to be below 15 percent before any priming. Paint on damp timber is the textbook cause of blistering and peeling because the moisture trapped under the film expands and breaks the bond.

For external steel and metal flashings the substrate needs degreasing, mechanical key and a primer matched to the topcoat. Skipping the etch primer on galvanised steel is a recurring defect because the topcoat looks fine for six to twelve months then sheets off in a single piece.

Moisture content and timing

The other timing rule that gets broken is the drying interval between coats. AS 2311 sets minimum re-coat times for each generic paint type. Two coats of low-sheen acrylic applied within an hour of each other will skin over and trap solvent below. The result is a soft film that fingerprints and marks easily.

Primer and topcoat compatibility

A paint system is a stack. The primer has to bond to the substrate and the topcoat has to bond to the primer. Mixing an oil-based primer with a water-based topcoat on a poorly prepared surface causes intercoat adhesion failure. The defect looks like the topcoat is peeling off in sheets while the primer stays put.

Specification documents from major Australian paint manufacturers (Dulux, Wattyl, Taubmans, Haymes) all set out the approved primer and topcoat pairings for new construction.

Common defects at handover

The defect register at practical completion almost always includes paint items. The most common ones are:

• Drummy or flaking paint over plasterboard joints, usually from dust under the sealer.
• Blistering on timber architraves and skirtings from high substrate moisture.
• Brush marks and ropy texture from overworking the film or working in direct sun.
• Uneven sheen across a wall, caused by inconsistent roller technique or patch repairs that were not blocked back across the whole wall.
• Picture-frame effect around cut-in edges from a different application method on the edge versus the field of the wall.
• Mould on ceilings in wet areas, almost always a ventilation issue rather than a paint issue.

External defects include chalking on north and west walls where a low-grade paint has been used outside its UV exposure rating, and rust bleed-through on un-primed nail heads in fibre-cement cladding.

Mould and ventilation

Mould growth on a painted surface inside a new home is one of the most disputed defect categories in Australia. The paint film cannot stop mould if the conditions favour it. Bathrooms without an exhaust fan ducted to outside, laundries with no passive vent and unventilated robes against cold external walls all build up enough surface humidity for mould to form within weeks. The National Construction Code Volume Two requires mechanical ventilation in wet areas.

Warranty position

Paint defects sit inside the statutory warranties for residential building work. In New South Wales the Home Building Act 1989 implies a warranty into every residential building contract that the work will be done with due care and skill and in compliance with the plans and specifications. In Victoria the Domestic Building Contracts Act 1995 implies the same warranty. Both cover paintwork.

The minor defect warranty period under the New South Wales Home Building Act is two years from the date of completion. Major defects are six years. Paint defects are usually minor unless the failure affects waterproofing or fire performance. Builders are required to rectify under the defects liability period and beyond if the work falls within the statutory warranty period.

Documenting a paint defect

Photograph the defect under raked light (a torch or work light held parallel to the surface). That throws shadows that show texture, brush marks and patch repairs that a flat photo would miss. Note the wall, the orientation, the time of day and the temperature. Paint defects sometimes only show under specific light. Get the evidence while the light is right.