A Window of Opportunity in Wood Restoration

Steinbeis expert Volker Bucher joins forces with timber manufacturing specialist Holzmanufaktur Rottweil to develop innovative methods for cleaning, abrading, and coating surfaces

Sometimes all it takes is a smidgen of fortune to bring innovative partners together. That’s how it was for Volker Bucher, professor at Furtwangen University and Steinbeis Entrepreneur at the Steinbeis Transfer Center for Surface and Coating Technology. He was walking around the Minster of the Holy Cross in Rottweil when he stumbled across Fabian Schorer, an expert in restoration work. As a specialist in restoring listed artefacts, Schorer was carefully cleaning frescos on the ceiling of the 800-year-old minster with a laser beam and stripping down wooden elements on the pews. This aroused Bucher’s interest … perhaps this laser cleaning technique or a similar process could be used to restore old wooden window frames. The two are now working together on a joint project with Rottweil Wood Manufacturing (Holzmanufaktur Rottweil). Their research and experiments are being funded through an innovation voucher awarded by the State of Baden-Wuerttemberg

In Germany, preserving windows on protected buildings is a cultural obligation enshrined in law. Aside from factors relating to architecture, building culture, and architectural heritage, it is an established institution offering immense potential in terms of environmental protection, sustainability, and resource efficiency. But preserving wood or metal fittings in old and listed buildings is only possible if you have access to effective means and solutions in terms of handicraft knowledge and restoration skills. In 2015, Rottweil Wood Manufacturing (Holzmanufaktur Rottweil) and holzmanufaktur SWISS from Hunzenschwil in Switzerland embarked on a series of research projects looking at the preservation and functional enhancement of old windows.

Working alongside Steinbeis expert Volker Bucher, the team at Rottweil Wood Manufacturing set about optimizing the methods of laser cleaning and CO2 snow-jet cleaning. The aim of the project partners is to find a way to selectively remove paint and other coatings from listed wooden parts, metal components, and other metal fittings. In doing so, the process should not affect – and especially not damage – underlying elements.

Searching for alternatives to lye removal and sanding

The team working on the project is using powerful experimental devices with an emphasis on high-energy light in the UV and IR wavelength ranges, opening the door to a whole spectrum of applications and answering a variety of requirements. It is also looking for effective alternatives to standard methods used to date in this area, such as chemical lye removal and mechanical grinding. These methods are not only hazardous to health, but also cause high levels of emissions and result in material losses; they may also affect underlying materials.

For the first step, Bucher conducted a feasibility study with the experts at Rottweil Wood Manufacturing. As the client, Rottweil Wood Manufacturing defined requirements and assessed these with Bucher in terms of practical feasibility. This was followed by a literature search, before selecting any methods that should be used and objects that could serve as a point of reference.

The CO2 snow-jet process

Research into commercial aspects affecting the CO2 snow-jet process highlighted the potential and the marketability of the method under investigation. Even highly sensitive surfaces of cultural importance can be cleaned with this process. Cleaning involves several steps. First, light surface patina is removed from areas of soiling using pulse transmission. Temperature differences between the CO2 snow jet and the surface being treated, as well as the thermoelectric voltage that this creates, take the process into the next stage of cleaning: The upper layer of the surface, which is subject to mechanical stress, is loosened by the pressure of the jet. During the cleaning process, the CO2 snow jet changes state from solid to gas.

Using lasers to clean materials with light

Another key area being looked at under the project in Rottweil is laser-based cleaning with light. There are already a number of reliable laser methods that can be used to clean, paint-strip, or pretreat wood and metal surfaces. Based on these approaches, Rottweil Wood Manufacture asked restoration experts already experienced in laser-based ablation to draft a work schedule for Steinbeis expert Bucher to complete for the project.

Atmospheric pressure plasma processes

The project team aims to conduct further testing and a series of trials in order to find ways to increase the weather resistance of indigenous types of wood. Many functional fittings on monuments – such as windows, doors, and all kinds of wooden parts – are subjected to aging, especially in outdoor areas exposed to the elements. As a result, they are not guaranteed to enjoy lasting protection and this makes them more difficult to care for, maintain, and work on.

The team is currently using a process involving atmospheric pressure plasma to conduct a series of tests aimed at improving the adhesion of coatings on wood from different sources, as well as wood with aging surfaces. This is expected to result in improved adhesion, deeper penetration, and more even distribution on surfaces. As provided for in the work schedule, lab testing is currently being carried out, as well as field testing involving outdoor weathering.


Prof. Dr. Volker Bucher (author)
Steinbeis Entrepreneur
Steinbeis Transfer Center: Surface and Coating (Rottweil)

Hermann Klos (author)
Holzmanufaktur Rottweil GmbH (Rottweil)

Fabian Schorer (author)
Restoration expert (Kusterdingen)