It happens all around the world: under cover of darkness, a graffiti artist whips out a spray can and his paint etches its way into the the wall. A new silicone-based technology claims to finally deliver an anti-graffiti effect that lasts while considering the special needs of architectural substrates.
“In porous masonry, the paint can penetrate down to a depth of about one millimeter,” says Prof. Helmut Weber, founder of the Competence Center for Building Protection and Renovation in Ebersberg near Munich, Germany.
“It literally clings to rough sandstone surfaces and is highly tenacious,” notes the construction expert. A great deal of water, special chemicals and a high-pressure cleaner are needed to remove the graffiti. Even so, the outlines of the inscriptions can often still be seen afterwards.
Spray paints getting cheaper
“Spray paints are becoming cheaper and thus affordable for everyone. Consequently, the spotlight is increasingly being turned on technologies that can provide buildings with long-lasting protection against graffiti and other defacements”, explains Marianne Kreuzpointner, a marketing expert in construction chemicals at Wacker.
One such product is already available in the USA. Applications engineer Hartmut Ackermann and his research colleagues from Wacker have taken this technology and enhanced it. “Like most anti-graffiti systems, our new product forms a continuous film on the substrate, where it acts as a barrier between the substrate and the spray paint”, says Ackermann. “The graffiti is unable to develop permanent adhesion to the silicone and so can be removed with cold water and a cloth or a high-pressure cleaner”, explains the chemist.
Anti-graffiti test in the “real world”
Tests in Germany have proven how well the product works. An underpass for cyclists was treated with the new anti-graffiti coating in the Bavarian town of Burghausen, which is also home to Wackers production site. “We deliberately chose a concrete wall that is a favorite target for graffiti,” says Albert Günthner, head of the department responsible for the town’s upkeep.
When the 20-m² test area was cleaned, Günthner witnessed for himself how effective the anti-graffiti protection is. “Before this, we had to use sandblasters to clean the defaced concrete walls, because the paint penetrates so deeply into them. Thanks to this new anti-graffiti product, all we need now is a high-pressure cleaner and cold water”, says Günthner. The researchers also addressed ealth and safety aspects by basing the product’s adhesion promoter and crosslinker on harmless silanes – not on an oxime and tin crosslinker.
Clear or pigmented coatings possible
The active-agent concentrate has the consistency of honey and should be diluted with a solvent before use. “Manufacturers of building protection agents can also add pigments to make colored coatings”, says Kreuzpointner. The active-agent content, viscosity and color are infinitely adjustable. Applying the anti-graffiti coating is possible by brush, roller or spray. The protective film makes the colors of the substrate appear more intense and adds a hint of gloss to the surface.
The anti-graffiti coating bonds especially well to mineral substrates like concrete, brick, plaster, marble and limestone. If a special primer is used, it can also protect glass and metal. Like most silicones the molecules anchor themselves in presence of atmospheric moisture by forming covalent bonds with some of the mineral components while also crosslinking with each other.
No cracks and irregularities
“The protective film is about 0.2 mm thick and can be stretched by up to 160 % before it tears. This allows cracks and irregularities to be bridged effectively”, explains Ackermann. Under normal conditions, the protective coating cures to a tack-free surface in two to four hours. After six hours, it is already firm enough to be cleaned. “A commercially available high-pressure cleaner can then be used to remove graffiti without any problems”, says Ackermann. “You don’t generally need to resort to any special chemicals.
According to test that Wacker did the anti-graffiti film is still as good as new even after having been cleaned 20 times without any loss of functionality. “A reliable anti-graffiti effect can be obtained with 200 to 250 grams of our silicone product per square meter”, explains Kreuzpointner. “The coating is permeable to water vapor and therefore much more breathable than polyurethane-based counterparts”, says the expert.
Permeable to moisture
For building expert Weber, that is the salient point: “Moisture transport must not be hindered, especially in the case of coarse-pored building materials such as sandstone, because otherwise the growth of microorganisms would be promoted or parts of the surface could spall.”
With or without anti-graffiti protection, one thing is paramount: unwanted graffiti, posters and other defacements should be removed as quickly as possible. After all, once a building has been defaced, it doesn’t take long for copycats to appear on the scene.
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