The protective film produced by temporary systems consists of waxes, biopolymers or acrylates. These materials do not prevent water vapor from migrating out of the substrate and into the ambient air and they are invisible, which is why they can be used on registered historic landmarks. The disadvantage of these systems is that the protective film has to be completely reapplied after cleaning off the graffiti; even without graffiti attacks, these coatings only last a few years.
The major advantage of permanent anti-graffiti systems is that they remain intact when the graffiti is cleaned off and can last many years without losing their ability to protect the surface. The downside, however, is that they usually affect the appearance of the substrate. In addition, the coatings of many traditional permanent systems are so dense that water vapor cannot penetrate them. If a coating that inhibits diffusion in this way is applied on a damp substrate, the moisture inside will not be able to escape. The protective film then comes off in some places as a result, potentially causing blisters to form or the paint to flake off; moisture damage to the building fabric is a possibility as well – a problem that does not arise with SILRES® BS 710. Traditional permanent coatings are based on substances such as polyurethanes, epoxy resins and fluoropolymers.
In semi-permanent coatings, only one component of the film is lost during cleaning rather than the entire film itself. The substrate has to be treated again every time graffiti is removed and at intervals of three to five years. The advantage of semi-permanent coatings is that they are virtually undetectable to the eye and are permeable to water vapor. These products often consist of blends of organic waxes, silanes and siloxanes.