Historical buildings and monuments were often made of sandstone. This has the advantage that it is easy to work with compared to granite or basalt. However, it has the disadvantage that it is not very weather-resistant. Therefore, parts or whole sculptures often have to be replaced as part of the preservation of monuments. Here, the question often arises where to get the replacement – if the former quarries are no longer accessible?

An alternative is now being developed jointly by WZR ceramic solutions GmbH (Rheinbach), Opus Denkmalpflege GmbH (Berlin) and the Chair of Construction Chemistry and Polymer Materials at Bauhaus University Weimar. The basic idea is to produce synthetic sandstone using the 3D printing process of material extrusion. This material should show the necessary properties for the application in the preservation of historical monuments without a thermal post-treatment. The consolidation is achieved by geopolymers, which are characterised by the fact that their production has a significantly lower environmental impact than the production of ceramics or cement.

The 3-D printing of sculptures and components of listed buildings and the production of stone substitutes with geopolymer binder systems require the development of new production technologies and specially adapted and coordinated binder systems. Especially the adjustment of rheological properties and reaction kinetics require a high degree of material development. In addition to the development of the geopolymer binder system, novel additives must also be developed in order to adjust the desired rheological properties.

In contrast to an object carved out of a stone by a stonemason, material extrusion can produce a hollow structure with only an inner supporting framework. This also makes large objects much lighter, which makes the work of the restorer much easier.

The outer contour is given by 3D data, which are taken from the original by scanners and digitally reworked. The surface is additionally provided with an allowance. This enables the restorer to manually rework the surface created by means of 3-D printing. In this way, he gives the object a surface that corresponds to that originally produced by the stonemason.

The project is funded by the Federal Ministry of Economics and Energy within the framework of the Central Innovation Programme for Medium-Sized Businesses (ZIM).

Contact: Dr. Dieter Nikolay, WZR ceramic solutions GmbH: d.nikolay@wzr.cc

3-D printing of natural stone for the preservation of monuments