Lithium silicate admixture in mortars to be used as putty for limestone

Abstract

Marble is a very common material in artworks for its softness, relative isotropy and homogeneity and its characteristic waxy look that gives "life" to sculptures. Even if in geology the term "marble" refers to metamorphosed limestone, commonly the term ‘marble’ is used more broadly encompassing hard unmetamorphosed limestone that can be polished assuming a glossy aspect. In the restoration field when marble artworks have cracks that alter the smoothness of their surface, a putty is used to fill them, for both aesthetic and conservative reasons. Putties usually consist of epoxy resin mixed with marble powder. The use of a synthetic resin raises some doubts on compatibility and durability of such putties, on the other side an inorganic binder, such as natural hydraulic or slaked lime, lead to a mortar that can’t be polished and doesn’t fit the aesthetic purpose of the putty. In this work, it’s studied the use of lithium silicate as admixture to improve the characteristic of inorganic mortars, particularly mechanical resistance and surface hardness in order achieve a good workability of the mortar surface. The mortars underwent compression and three-point bending tests to measure the influence of lithium silicate on mechanical properties, capillarity test and equilibrium water content to verify modification on the interaction with environment, abrasion resistance tests to study surface hardness modification. The results clearly indicate that lithium silicate in low percentage allowed to obtain a more resistant mortar, characterized by a harder and more compact surface that can be polished in order to resemble marble smoothness. Moreover capillarity rate decreases while equilibrium water content increases slightly, indicating that the treatment affect only a little the interaction with environment. Finally the mortars can be painted using lithium silicate as binder for watercolour so that these mortars can be used not only on white marble but also on coloured limestones.