ConNext-2021

26 Consolidation of heat blisters in relation to a painted door of the wooden interior of the Ruppertsberg teahouse KEYWORDS: fire/heat blisters, blister treatment, Ruppertsberg teahouse, consolidation, synthetic adhesive. This paper addresses the damage phenomenon of heat blisters, their formation and their conservation treatment. The term ‘heat blisters’ is used to describe deformations in the paint layers due to considerable heat (from a temperature of 75°C). This type of damage was found on a painted door that is part of the wooden interior of the Ruppertsberg teahouse (1842). Using this door as an example, a concept for flattening and consolidating the heat blisters was developed and applied. The formation of heat blisters can be briefly described by the following process (see figures, top): Extreme heat causes thermoplastic softening of the paint layers. At temperatures above the softening point, the so-called pyrolysis starts. In this process, gases are developed that exert an extremely high expansion pressure on the strongly softened paint layers and blisters form. The persistent heat moves further into the deeper layers and more blisters form. This results in layer separation, stomata and the bursting of blisters. The elasticity of the painting steadily decreases due to an ever increasing cross-linking. The paint becomes brittle and is no longer possible to return to its original state. On the basis of published methods for the treatment of heat blisters, the authors agree that it is possible to make the blisters more flexible and thus flatten them by the use of heat. The combination of an infrared lamp and a heating spatula proved to be suitable on the door. The additional application of a consolidant was necessary. This made it possible to achieve adhesion between the individual paint layers as well as to the carrier. An acrylic resin dissolved in solvents (Plexigum PQ611 in petrol) was used. According to the surface of the blisters, two methods were developed that were applied successfully to the entire object (see figures, bottom). Due to the strong expansion of the voluminous blisters with a simultaneously constant carrier size, however, the formation of small wrinkles and puckers could not be avoided completely. Nevertheless, this slightly irregular structure will only be visible on closer inspection. carla.helmrich[at ]stud.hawk.de