During the air-brushing application, sample surfaces were kept at a distance of
about 40 cm from the nozzle (diameter: 1.5 mm) of spray gun. Travertine surfaces
were coated with 25 ml/m2 (C1 treatment) or 70 ml/m2 (C2 treatment) on average.
After spray deposition, treated specimens were dried in a ventilated oven for 1 h at
about 70 C. This drying phase is not strictly necessary and can be avoided in real
outdoor use on stone surfaces, since it simply accelerates the normal process of drying.
Any other additional or subsequent thermal treatment was avoided
since it is not always possible to use thermal processes on outdoor building stones,
both in the field of Cultural Heritage and modern architectural surfaces.