Fluorinated anti-graffiti coating for natural stone

Abstract

The water- and dirt-repellent properties of fluorinated products have been used primarily in waterproof coatings. The development of new materials or the definition of new functions for existing substances may extend the possible application of these systems to other specific uses, such as new anti-graffiti coatings to guarantee easy clean-up in the event of this kind of vandalism.The present study aimed to assess the anti-graffiti protection afforded by a fluoralkyl siloxane in limestone and granite.The results show that the surface of the substrates darkened and yellowed slightly under the treatment and that the total colour variations (ΔE*) found after the first cleaning were similar in the two substrates. After subsequent graffiti painting-cleaning cycles, ΔE* was greater in the granite, due to its more rugged surface. Water absorption declined, particularly in the low porosity granite, after it was coated. Water repellence was likewise more effective in the granite, whose low initial permeability decreased, but less steeply than in the limestone. The graffiti lowered the water repellence of the treated surfaces. Although the waterproof protection afforded by the coating was not fully recovered after cleaning, the treated specimens were still more water repellent than the uncoated stone. The siloxane polymer penetrated the limestone to a depth of several tenths of a micron, but remained on the surface in the granite.