An innovative phosphate-based consolidant for limestone. Part 2: Durability in comparison with ethyl silicate

The durability of a new phosphate consolidant for limestone, based on formation of hydroxyapatite (HAP), was investigated in comparison with ethyl silicate (ES). Untreated, HAP- and ES-treated samples were subjected to repeated wetting-drying, freezing-thawing and salt crystallization cycles. The weathering effects were monitored in terms of alterations in visual appearance, weight, dynamic elastic modulus, tensile strength and pore size distribution. HAP samples performed better than untreated samples and underwent less deterioration in original properties than ES samples. ES samples, subjected to salt crystallization cycles when the treated layer was still hydrophobic, experienced detachment of the consolidated layer.