All water-based wall paints contain water-soluble components: dispersants, wetting agents, thickeners, glycols and surfactants that eventually leave the paint on exposure. Surfactant leaching or streak staining occurs when these ingredients leach out of the paint by rain or dew after application during the initial curing process and should ‘weather off’ after about a month unless baked in by the sun.
Darker paint colours generally show the leaching more, although it can also occur with white and light colours. Sometimes the stain appears as a tan colour. Carol Ras, Plascon’s Professional category manager, advises that the best way to deal with surfactant leaching is to just leave it alone for the first few weeks, and give the paint job a chance to self-correct. “Trying to remove the blotches or shiny streaks from a paint job can be tough and could result in the paint’s film integrity being compromised before it has had time to cure properly,” she says.
“The exterior durability of the paint is not damaged by surfactant leaching. The best course of action is to wait it out patiently and monitor the weather conditions, as these have a direct impact on the paint, particularly in the initial drying-out phase. Newly-painted surfaces that are exposed to rain or dew can be more susceptible to weeping, as the dampness draws the water-soluble components to the surface.”
In serious cases of leaching, the stains may reappear several times until all the surfactant has gone. Only in extreme cases is a repaint necessary when the blotches stain the painted surface permanently.
“The best advice I can give,” says Ras, “is to check the weather before you paint – if damp conditions are forecast, rather wait until the next day.”
Plascon’s water-based, exterior paints are formulated with the minimum amount of water-soluble ingredients to help reduce surfactant leaching, however, in any coloured or tinted paints, the addition of the colourant can reduce these benefits as the universal dyes contain surfactants.
Darker paint shows leaching more than lighter colours. Photo source: Patrick Baty www.patrickbaty.co.uk
Painters and building owners can rest assured that streaks will wash off days after the paint dries or ‘weather off’ after about 30 days. Photo source: www.masterpainters.co.nz