Prékopa Ágnes (szerk.): Ars Decorativa 31. (Budapest, 2017)
Kornélia HAJTÓ: Restoration Options for Architectural Ceramics
rior and interior work, a marked change from the past. Several companies offer products expressly for restoration purposes. The construction industry has also responded to the demands of restoration of historic buildings, developing construction materials with a wide range of properties. In practice, restorers have to determine the suitability of these materials for specific applications by experiments and tests. Only the test of time, however, can establish the true fitness of a new material. Part of a restorer’s job is to return to previous restorations from time to time and check their condition. This tells us much about the durability and long-term applicability of the materials used. There are few materials offered specifically for the restoration of exterior ceramics. Most often, we use materials that have been developed for stone restoration. This assumes that the ceramic has functions and material properties close to those of stone. There are two broad categories of fired clay elements used on buildings: terracotta (plain fired) and glazed (majolica) ceramics. These embrace a wide variety, and Zsolnay products, for example, span a very wide spectrum of material and manufacture in both categories. One particular class of ‘special terracottas’ is now universally referred to as pyrogranite. In general, restoration follows the phases of cleaning, conserving or strengthening, adhesion, addition, retouching and surface protection. We will look at each of these phases in turn. Cleaning Atmospheric pollution exerts severe stresses on the outer walls and roofs of urban buildings. The air in cities nowadays contains high concentrations of solid- and gas- phase components that contaminate and disfigure the surfaces of buildings. There are three basic means of removing contamination: chemical removal, sand-blasting and steam cleaning. The simplest cleaning chemicals are surfactants. These are asymmetric molecules, with hydrophilic (polar) ‘heads’ and hydrophobic (apolar) ‘tails’. They include detergents and soaps. Surfactants work by surrounding apolar, i.e. non-water-soluble particles and dispersing them in water so that they can be washed off. The most commonly used surfactants in restoration practice are anionic fatty alcohol sulphates, specifically alkyl sulphates. There are cleaning agents on the market today that have been developed expressly for facades. One is Fassadenreiniger Paste by Remmers. Its technical data sheet states that it is ‘suitable for cleaning every faţade of clinker, brick and stone, and sculptures.’ It is a mildly acidic (pH 5) ammonium chloride containing paste, applied to the surface and left to act for about five minutes, after which it is washed off by a jet of water. The cleaned surface is then neutralized as prescribed. It may also be used to clean glazed ceramics that are in good condition if diluted and applied for a short time, under the supervision of a specialized restorer. Proper care is necessary, however, to prevent it from etching the surface of the glaze. Another Remmers product is Alkutex Abbeizer, an acid-free etching cream for cleaning graffiti and paint out of pores. It degrades biologically. The only information on the data sheet is that it is mildly basic (pH 8.5). A faţade cleaning agent made by Ter- ranova is Weber E 709. The data sheet re95
