Hydration_Dehydration decay on sandstone: possible remedial and evaluation of the effects of a specific anti-swelling product

Hydration and dehydration processes constitute a crucial issue for the conservation of sandstones, where a certain amount of swelling clays is present. Very often flaking and micro-detaching are produced, when this mechanism act on sandstones. Nevertheless, the topic is quite neglected in recent literature. In order to prevent the clay swelling, hydrophobic treatments are usually applied. A comparative assessment among several products on decayed surfaces is carried out in this study. In particular, different combination between consolidants (CONSOLIDANTE DN - ethyl silicate; and VP 5035 - modified ethyl silicate, both by Chem Spec) and water-repellent products (Fluoline HY by CTS Europe - fluoroelastomer - and BSM40SKY - alkyl silane - by Chem Spec), with and without anti-swelling product (AntiHygro - Remmers) were tested in laboratory and in situ at the St.Prospero Tower in Reggio Emilia (Italy). The tower, currently under restoration because of a severe damage due to exfoliation, scaling and detaching, is constituted by sandstones quarried on the Apennines (Monte Cassio, Ranzano and Pantano). The laboratory tests were carried out on the same sandstone materials, sized on purpose. Ultra close-range photogrammetry technique was utilized to evaluate the effects of the anti-swelling product, both in laboratory and in situ on selected areas with different state of conservation and exposition. The monitoring of treated surfaces, with respect to the non-treated areas, was performed in order to evaluate variations of the surface morphology over time. The assessment of the products effectiveness was completed by colorimetric analyses, water absorption tests (capillarity and contact sponge method), static angle measurements and water vapour permeability tests