The volumetric and chromatic reintegration of hydraulic mosaics: comparison between four different techniques

Abstract

The mosaic made of hydraulic tiles, is an architectural coating with a significant decorative importance, characteristic of both modernist and Art Deco architectures. This technique appeared in France in the decade of the 1860s, spreading all over Europe with great rapidity, and with a remarkable impact until the beginning of World War II. The decoration with hydraulic mosaic is based on the use of tiles made of compressed cement, adorned with intense colours and a glossy appearance. After been used for more than a century, many of these decorations are in need of an immediate intervention. As they are serialized and mass-produced elements, their volumetric and chromatic reintegration becomes easier. Non-interventional procedures are not usually acceptable, as they often have pavement function. In this work, four different restoration techniques have been compared. Starting from inorganic binders, we have proposed 1) white cement / silicate mineral paint; 2) acrylic resin / paint and 3) epoxy resin / paint. Last, reintegration tests were made on marble stucco using a combination of plaster, pigments and animal glue. The results of these four systems were compared with the ones obtained from the traditional hydraulic mosaic, paying special attention to gloss, hardness, and porosity. As the goal is to choose the most appropriate technique applied to Cultural Heritage, its behaviour was tested through two accelerated aging tests. On one hand, a group of test samples have been exposed to the penetration of salts by capillarity, very common in pavements. On the other hand, the samples were placed in a climatic chamber with the aim of accelerating its aging, exposing them to humidity, heat and UV radiation. These tests have made possible to know the potential of each of these materials and their suitability for volumetric and chromatic reintegration.