Restoration of 20th century murals

SRAL possesses extensive expertise in the restoration of twentieth-century murals. The organization has handled notable projects such as Henri Jonas's Marian cycle (1926) in the Koepelkerk, Maastricht; the painted interior of St. Cunibertus Church (1946) in Wahlwiller by Aad de Haas; and Hans Truijen's murals (1978) in the Catharinakapel, Lemiers.

Causes of damage

These restorations illustrate the various causes of damage to paint layers on walls and underscore the extensive research needed for accurate diagnosis and treatment. Moisture is a significant factor in decay, as it can dissolve the binder in paint, making it highly vulnerable. When salts dissolve in the walls, the resulting crystals can pulverize the plaster and dislodge the paint layer as it dries. This type of damage was evident in all the mentioned paintings.

Another major cause of deterioration is the use of unsuitable paint types for murals or improper application methods. For instance, Hans Truijen used acrylic paint in Lemiers to achieve vibrant colors. However, the paint’s vapor-proof nature contributes to significant flaking. Over time, the elasticity of acrylic paint decreases as the binder molecules cross-link, and at very low temperatures, the paint becomes stiffer and more brittle. Consequently, paint peeling becomes inevitable.

Treatment

One paint type well-suited for wall applications is mineral Keim paint, which was specifically developed for this purpose. It is vapor-permeable, low-stress, and has excellent aging properties. However, improper application can lead to problems. For instance, in Maastricht’s Koepelkerk, the paint was found to be incompatible with a lime and plaster substrate.

In the case of the paintings in St. Cunibertus Church in Wahlwiller, a thorough review of the restoration history was essential for effective treatment. During the 1980s restoration, a varnish layer was applied, under which some dirt was partially concealed. While removing this varnish was considered—since colors are often more vivid without it and varnishes become increasingly difficult to dissolve over time—the decision was complicated. Previous conservation reports indicated that significant parts of the painting had been reconstructed due to severe salt damage in the walls. Thus, removing the varnish was deemed impractical.

SRAL possesses extensive knowledge of materials and techniques used in wall paintings from the interwar period, as detailed in the book chapter "The Grace of the Scaffold" by Bernadette van Hellenberg Hubar.