Fair-faced concrete answer for modern architecture in historical setting
With its famous water features and, in particular, Hercules Monument, Kassel’s Bergpark can be regarded as the city’s best-known landmark. The monument itself crowns the highest point in the park and has now been given a new visitor centre.
The client for the new building, which cost almost €3.5 million and has a floor area of approx. 750 m², was the Federal State of Hesse . Formwork panels from Westag & Getalit AG were used to comply with the high demands placed on the fair-face concrete surfaces.
Relief-type façade texture
The task of integrating the modern architecture into the historical surroundings was solved with fair-face concrete. The architects from Berlin designed a polygonal figure with a special relief-type texture for the façade which could be built in class SB2 fair-face concrete. Located directly in front of the Hercules Monument, the entire structure is a direct reference to this local landmark. To achieve a perfect balance between the façade and the tuff stone of the monument, and between the new entrance to Kassel’s Bergpark and this historical site, the complete façade was subsequently sandblasted.
As a contrast to the uneven look of the façade, the entire interior of the visitor centre was given an SB4 finish (the highest class of fair-face finish). The smooth fair-face concrete wall surfaces and soffits therefore provide a modern contrast to the wooden furnishings, but still fit in well with the style of the interior. Both inside and outside, all the details of this building have been carefully and thoroughly conceived, which meant that the various openings for doors and windows, even the recesses in the soffits for the flush-fitting lighting units, had to be constructed very accurately in order to do justice to the requirements placed on the design.
Extensive testing and sample panels
Complying with the requirements placed on the immaculate fair-face concrete surfaces required a considerable number of sample panels. The contractor responsible for the structure therefore prepared numerous samples in order to select the right formwork board, release agent and concrete. Indeed, a complete wall was built in advance with the relief-type texture in order to minimize further problems during construction.
A total of approx. 1500 m² of Westaspan 450 SP was supplied for this project. This board, suitable for formwork to large areas, has a 450 g/m² film coating on both sides, which makes it ideal for all smooth, seamless concrete surfaces with a matt look. Another advantage for work on site was the factory-cutting of the panels: there isn’t a single 90° angle anywhere on the structure – a fact that placed high demands on the formwork. On site, the prefabricated panels were able to be directly erected for the walls and slabs without the need for time-consuming cutting to size. The boards were used in a panel formwork system.
Fair-face concrete throughout posed a real challenge
The formwork for the relief-type façade proved to be especially difficult and time-consuming. Boards in a huge variety of different lengths, widths and thicknesses had to be added to the formwork panels by hand to give the façade its special texture. To cope with the ensuing offsets within the textured façade, the site management decided to use a virtually self-compacting concrete (F6). Consequently, such a very fluid concrete mix called for well-sealed formwork to ensure that the desired final form was not spoiled.
Another challenge was the inclusion of movement joints. In order to avoid disturbing the pattern of horizontal and vertical lines on the façade, all joints were incorporated into the layout of the formwork panels to create a homogeneous appearance. The façade with its formwork in SB2 quality was subsequently sandblasted to match its historical surroundings – especially the tuff stone of the Hercules Monument.