Graffiti Defense - Wacker Chemie AG

Graffiti Defense

Good Adhesion on Concrete and Brick

Not only is the concentrate easy to process – it is also quite simple to apply coating compounds made from SILRES® BS 710 as well: they can either be sprayed onto the substrate or spread on with a roller or brush.

The coating starts out as a liquid, but when exposed to atmospheric humidity, it cures from the outside in. The surface is no longer sticky after about four hours. A curing time of a day or more produces a strong silicone film that permanently bonds not only to many porous mineral substrates, but also to wood and epoxy resins – no need to treat the substrate with a primer ahead of time.

Adhesion tests have shown that the most suitable of these substrates are concrete, brick, plaster, sandstone, sand-lime brick and natural stone. The tensile adhesive strength of unprimed sand-lime brick, for instance, has been measured as 1.30 N/mm2 – a value frequently encountered in the construction materials industry for floor coatings on mineral-based substrates. Tests also showed that glass or painted metals need to be treated with a suitable primer in order to achieve the adhesion necessary.

“Thanks to SILRES® BS 710, the building protection industry now has a highly effective concentrate at its disposal for use in permanent anti-graffiti coating agents.”

Dr. Rudolf Hager Head of the Construction Silicones business team

Vapor Permeable with an Abhesive Surface

WACKER anti-graffiti protection is particularly suitable for infrastructure such as bridges, underpasses and subway stations.

A key property of silicone films made from SILRES® BS 710 is their exceptionally abhesive surface – a surface, in other words, to which other substances do not adhere well at all. As a result, graffiti can be washed off with cold water using a sponge or commercially available pressure washer – no special cleanser required – while posters and signs either fall off under their own weight or can be peeled off effortlessly.

Its abhesive properties are the result of the extraordinarily low surface energy of the silicone film. There are very few substances with lower surface tension, and, generally speaking, liquids are only able to wet and develop a strong bond to surfaces if the surface tension of the liquid is lower than that of the surface. This same principle applies to spray paints and to the adhesives used on stickers – the surface tension in each of these cases is significantly higher than that of silicone and, as a consequence, they do not adhere well to the silicone surface.

The application technology specialists at WACKER found that application of 200 to 250 grams of SILRES® BS 710 per square meter is enough to provide reliable protection against graffiti. If the material is prepared correctly, the surface only needs to be treated once – the cured silicone film will then completely cover the pores in the substrate. The coating nevertheless remains permeable to water vapor. This has been confirmed by the sd value determined for layers of the cured material (see page 4).

The sd value for samples roughly 200 micrometers thick – which corresponds to the recommended coating weight of 250 grams of SILRES® BS 710 per square meter – was measured as 0.3 meters (class II, mid-range), which is below the sd value of traditional polyurethane coatings of equal thickness.