Stephanie McDonald reports on a paint product which binds to the substrate, and potentially lasting hundreds of years.
Everyone would be familiar with the strong, overwhelming smell of newly applied paint of the 80s and 90s. Fast forward to 2009 and there are a plethora of natural paints which give the same finish and texture as former paints, without toxicity levels associated with them.
Mineral paint has been used for centuries, with Caroline Edwards, marketing manager at Porter’s Paints, saying the ancient Egyptians produced silicate paints by melting sand and ash together to paint walls and frescoes. Silicate-based paints have also been discovered in the ancient ruins of Pompeii and Heracleum.
“In 1768, JW v Goethe described it as ‘iquor silicium’, which emerges if one melts pure quartz sand with an adequate proportion of alkali, whereby a transparent glass is obtained which melts in connection with oxygen and gives a beautiful clear liquidity,” says Edmondo Rosini, national sales manager at Colours By Nature. “Natural paint manufacturers use pigments that include earth minerals and iron oxides, with the fillers like marble dust.”
One of mineral paint’s key advantages is its durability, with Porter’s Paints’ mineral products coming with a 15-year guarantee against cracking, peeling and fading. Mineral paint is also non-flammable, contains no solvents except for pure water, and “light rays and thermal rays are reflected. This reduces the thermal stress on the building structure and thereby reduces the potential for the substrate to crack,” says Rosini.
Lacoste + Stevenson used mineral paint on a heritage cottage restoration in Sydney because mineral paints helped the concrete render on the outside of the building breathe. “They would have used mineral paints back in the day and it just means the concrete render that goes over the brick can breathe so you get a much softer finish. If you put a plastic paint on it, it will trap the moisture and also has a glossy, plastic look,” says Sergio Corona, the architect for the project.
“The difference between going for the glossy and mineral look is huge. The colours are much more subdued and it doesn’t look so plastic.”
Corona recommends Porter’s Paints mineral paint products, which are a silicate based coating and contains low volatile organic compounds (20 g per litre), compared to a typical oil paint containing around 350 g per litre.
Mineral paint is mainly used for exterior surfaces such as render, concrete, bricks, stone and other masonry surfaces. Unlike standard paint, which is applied over the top and sits like an extra layer on the surface, mineral paint penetrates the surface and chemically bonds to the substrate.
“The cured paint forms an inorganic structure with a very strong bond to the substrate and cannot crack, peel or flake,” Edwards says. “Other paints using similar technology in overseas locations have lasted more than 100 years.”
Any surfaces which have previously been painted need to be stripped back to the original mineral surface before being coated with mineral paint to ensure the paint binds correctly to the surface. “The key to successful application is correct priming for the particular surface — hence the need for a professional who can assess the surface prior to application,” he says.
Mineral paint can be applied with a wide block brush. “If using a roller, use a synthetic cover with a 2.0 cm to 2.5 cm nap. Applying by spray gun is inadvisable because of the effects of alkaline over-spray on nearby glass, vehicle finishes etc,” Edwards says.
Porter’s Paints recommends the substrate should be cleaned and free of dirt, dust, grease, oil, mould, bond breakers and any contaminants that may compromise adhesion. Bare surfaces also need to be primed with a coat of mineral silicate primer, as the durability of the paint can depend on the surface quality and surface preparation.
When dried, the paint has a natural matte finish and comes in various colours, with typical earth colours including: red, ochre, yellow, green, blue, brown, umber, black and orange.
Colours By Nature uses natural pigments in its mineral paints, which are not formulated with acrylics and other petrochemicals. However, its products do require a special application process and are primarily for masonry and earth construction. “Consequently, their demand in Australia has been limited,” Rosini says. “Important to also note is that silicate paint will seal the wall surface and limit the transfer of moisture vapour.”
Mineral paint cannot be used on all types of exterior surfaces, however. It is not suitable for glazed bricks, glazed tiles, timber, metal, paperfaced plasterboard and fibrous cement sheeting. It will also not bond to synthetic compounds such as epoxy or silicone.
