11:40 – 12:05. LECTURE
The ticket booths from 1972 in the Olympic Sports Facilities Munich.
Conservation and maintenance strategies to preserve historic transparent acrylics in situ.
Susanne Brunner
Technische Universität München, Munich, Germany

Of the many small buildings, installations, and works of art that distinguished the “joyful games in the green”, only twelve of the original 1972 ticket booths and kiosks still exist around Munich’s Olympic Stadium. They are unused, neglected, and in poor condition, but listed as heritage objects along with the Olympic sports facilities.
The Professorship for Recent Building Heritage Conservation recently examined the ticket booth in the Northwest, in a study funded by the Meitinger Stiftung. The general aim was to determine the materials used, how the building was constructed, and what condition it is in now, with special attention to the original acrylic elements. The next goal was to develop concepts for future use.
The construction consists of steel pipe frames filled by aluminum walls. Transparent acrylic plates are used for the ribbon windows and barrel-shaped roofs. These plates are varnished with a dark lacquer, either on the outer or inner side, to provide interior shade. The acrylic plates, made of Plexiglas® GS 215, were cast, stretch-formed, bent cold into the aluminum frames, and then screwed onto the steel pipe frame. Company Röhm analysed the acrylic materials using py-GC/MS, revealing UV-adsorbents and flame retardants. The condition of the acrylics was examined macro- and microscopically in situ and documented. The acrylic plates show a variety of deformations and aging phenomena such as loss of lacquer, cloudiness, whiteness, scratches, (micro) crazing, breakage, flaking, and loss of material.
Reasons for the ageing phenomena can be assigned to atmospheric factors, especially UV-light, water, and oxygen, but also soot, tyre wear, plant particles, and mineral dust. Since most of those particles are hygroscopic, they function as a breeding ground for plants and microorganisms. Biologic colonisation (moss and fungi, for example) and biologic deposits (insect excrements and bird droppings, for instance) damaged the lacquer and the once glossy and smooth acrylic surfaces, which then became rough and grey. Whereas the biologic colonisation induced moderate damage, vandalism (that is graffiti tags and mechanical damage) and improper cleaning (that is using high pressure or temperature, abrasive ingredients, scratching tools, and solvents) caused severe damage. Especially problematic is the removal of graffiti tags and the sticky excrement of insects and fungi combined with sap from lime-trees.
As a result, less abrasive regular cleaning and gentler products are strongly recommended for maintenance and as a preventative measure. However, no general recommendations exist yet for proper cleaning of outdoor acrylics. Cleaning should be effective and suitable for acrylic components of various geometries. The product used should be environmentally friendly (i.e. the cleaning detergent must be biodegradable to protect the lake nearby), chemically not aggressive, and non-abrasive to protect the lacquer and scratch-sensitive acrylics. Accordingly, cleaning tests were performed in situ with Gregomatic®, Microfiber Cloth and a high-pressure cleaner. This latter method was used in contrast to other cultural heritage cleaning methods involving valuable/sensitive surfaces. First results were promising, though a methodologic approach examining the damage impact as well as the cleaning effect is recommended.
Further preventive and conservation measures should be considered and could include applying a protective coating and reshaping the deformed acrylic plates. After cleaning, a protective hydrophobic coating could ease the removal of new graffiti, stabilise already degraded surfaces, and slow down the degradation of acrylics. To close the gaps in construction, the strongly deformed windows could be reshaped by means of tempering, although tempering already degraded acrylics risks cracks and breakage. This process should be tested beforehand.

Susanne Brunner studied restoration, conservation science and art technology at the Technical University in Munich (TUM). She specialised on modern materials and plastics. Since 2019, she has been working on the conservation of outdoor transparent acrylics, first at the Deutsches Museum and since 2020 at the TUM Professorship of Recent Building Heritage Conservation in cooperation with the Deutsches Museum München and the Bayerisches Landesamt für Denkmalpflege (Bavarian State Conservation Office). Currently she is working on her dissertation on the same topic.