Deleterious effect plastic-based biocides on back-ventilated granite facades

- White plastic paint, Sikaflex®, Tegosivin® and Tegovakon® were tested on granite.
- Chlorophyll-a content of treated samples was statistically higher than controls.
- The colour changed significantly and statistically relative to control.
- Concentration of chlorophyll-a and colour were closely correlated (r2 = 0.95).
- Plastics to the back of granite specimens increase its tertiary bioreceptivity.

In Galicia (northwest Spain), the mild humid climate causes the walls of many buildings to be permanently damp, which leads to the appearance of phototrophic colonization (“greening”) on the walls. Prolonged, deeply penetrating damp can be halted by the application of plastic-based products. Ventilated facades are separated from the structural wall, which enables the protective products to be applied to the back of the facade. This is an important advantage since it allows the use of coloured paints, which would be unacceptable for use on the exterior face of a building, and other plastic-based compounds that are degraded by solar radiation. The main aim of this laboratory-based study was to evaluate the usefulness of several plastic-based products (viz. white plastic paint, Sikaflex®, Tegosivin®, and Tegovakon®) for inhibiting biological colonization on the exterior faces of buildings when applied to the back of the stone cladding. The results of the study demonstrated an unexpected effect: the application of plastic-based products to the back of specimens simulating ventilated granite facades does not inhibit biological colonization, but increases the tertiary bioreceptivity of granitic rocks.