Prékopa Ágnes (szerk.): Ars Decorativa 31. (Budapest, 2017)
Kornélia HAJTÓ: Restoration Options for Architectural Ceramics
a diamine polymerization reaction. Epoxy resin comes in several different forms and can be polymerized in different ways to produce material with a wide range of properties, so that we can, for example, always find one that forms an adhesive layer of the right elasticity. There is no doubt about the high cohesive and adhesive strength of synthetic resins, but there are uncertainties concerning how they withstand various weather factors and how they interact with inorganic, mineral materials and form a system with them. Cement-based adhesives also have a broad range of application. Cement-bonding adhesive mortar was originally developed to lay tiles. The main constituents are a wide variety of calcium silicates and calcium aluminates, which harden in a gradual crystallization process following hydration. Hardening results in a stone-like material whose properties can vary over a wide range depending on the different particle size of the cement and the action of additives. There are many products, such as Keraquick Grau, Keraflax and Ardex X7G, that are appropriate for restoration purposes. When they are cured, inorganic adhesives form a crystal phase that is undoubtedly close to that of the ceramic. The similarity of the materials makes them more likely to ‘cooperate’ and resist phenomena that lead to crumbling. It must be borne in mind, however, that before they harden they have a highly basic chemical action. In addition, the crystallization process continues for years, potentially leading to changes in rigidity and increasing strength. Altough we have looked at synthetic resin and cement-based adhesives separately, the two systems are often combined nowadays. Synthetic resin additives are used to change the properties of cementbonding materials. The long-term performance of such combined materials, however, is still unknown. Additions and patches Repairing defects in exterior ceramic elements is required where the priority is to keep the original artwork in place. This is true mainly for sculptures, fountains, and artworks that would otherwise have to be copied in their entirety. If the damage only affects a small proportion of the surface, it can be patched to restore the original appearance. Where large areas of exterior ceramic facing have been damaged, replacement with new tiles is often the preferred option, although ceramic elements can be patched or added to if it is important to retain the original. Additions and patches are made using ‘repair mortars’ which, like the adhesives described above, are systems that combine cement and synthetic resin. Examples are Ardex X7G, IMPA Canova, Keim Dolomitspachtel and Monulit. They have been developed for repairing stone, and thus have an appearance and other properties that allow them to blend in with a damaged piece of stone. Nonetheless, they have also been found to work well for exterior ceramics. Monulit, a Belgian product sold in Hungary by Technowato, is a two-component repair mortar intended for hard limestone. According to the data sheet, it consists of ‘a mineral binder and a filler: a special reaction is set off by mixing the powder with the fluid, making a mineral-based mortar that works its way into the stone it repairs and forms chemical bonds with it.’ The pale grey colour and texture of Monulit is very 101
