Performance testing of transparent protective coatings on globigerina limestone

Abstract

Tests were carried out on locally available protective coatings, including silicones, siliconates, polyvinyl acetates, acrylics, natural oils, and a siloxane, an aluminium stearate, and a polyurethane. The intrinsic properties of the products, including the specific gravity, viscosity, percentage dry weight and evaporation velocity, were first determined. The solutions were subsequently applied to Globigerina Limestone samples using total immersion, capillary absorption, and brush application. The degree of water-repellence of the treated stone samples was tested. The depth of penetration of the product was determined by staining, acid etching and by SEM. For the products that gave promising results, further tests were carried out, including accelerated weathering tests with prolonged exposure to UV light, temperatures ranging between 18 and 48 T, and relative humidities of between 70 and 99%. The artificially weathered samples, as well as samples exposed to the weather for four years, were then tested for residual water repellence. The tests included the measurement of the stone-water angle, the determination of the water drop absorption time, as well as of water absorption by total immersion and by capillarity. After accelerated weathering, it was found that silicone and siliconate products provided good water repellence, even after sixty 24-hour cycles. Acrylic products gave conflicting results; after natural weathering only acrylics continued to provide water repellence. Naturally weathered stone grew darker in colour to varying degrees. Artificially weathered treated stone did not undergo these aesthetic changes.