Today’s Pretoria Tower (also known as “Volkskas Building“ or “Absa Tower“) was erected at the end of the 1970s. The building not only was the first skyscraper in the rapidly growing metropolis of Pretoria, but also was considered as showcase project for modern construction at that time throughout South Africa. Thus, it is an architectural witness to history which – centrally located at the corner of Pretorius Street / Lilian Ngoyi Street – represents a landmark visible from far away within the business quarter of the city. This exposed position and its monumental, sculptural appearance make the Pretoria Tower a striking reference point, which has been a characteristic element of the cityscape for more than three decades.
The project rich in tradition has been adapted to the current building standards recently. Its previous facade cladding has been renewed and replaced by a modern ceramic solution with the objective of retaining the original look as far as possible. The reason for this was the fact that the Pretoria Tower is protected by the “National Heritage Resources Act“ (a kind of legal protection of historic monuments) as an “outstanding architectural achievement of a remarkable architect“. The great significance and the high quality of the original design concept of “Pauw and Botha Argitekte“ are also underlined by the medal of honour received from the South African Institute of Architects. Against this background, the initiative for the restoration of the Tower founded in 2010 attached great importance to a renewal of the facade in such a subtle manner that the silhouette, the structure, the cubage of the building and aesthetic characteristics are basically maintained. However, an analysis of the architecture office Boogertman + Partner had shown that this could not be realized by a restoration of the existing facade and that it would have been impossible to meet the current requirements with regard to construction technique in this way.
That is why a modern alternative was looked for and found in the form of facade ceramics made in Germany. The system KeraTwin of the brand Agrob Buchtal satisfies the elevated design and functional requirements in several ways:
The colouring of the glaze was adapted to the original look as exactly as possible, and the relevant parts of the substructure were also powder-coated accordingly. In total, Agrob Buchtal supplied more than 30,000 square metres of facade ceramics and the appropriate accessories for the installation. An essential feature of the system KeraTwin is the intelligent fastening, which permits an economical and efficient mounting – an advantage which comes in particularly useful in view of the huge dimensions of this project. The glazed ceramic panels made of high-quality stoneware are simply hung in vertical rails via holding grooves on the reverse side without using any additional tools. Compression springs and removal protections integrated in the system rail prevent clattering and constraining forces e.g. in case of alternating wind loads, which may occur at this building with a height of approximately 140 metres. In addition, precisely adjusted vertical joint profiles reliably secure the position of the panels. At the same time, an aspect is elegantly realized which seems to be contradictory at first glance: certain provisions prevent the removal of individual panels by unauthorized persons, while experienced experts have access without destroying the material, if necessary.
Apart from visual and technical aspects, however, the new ceramic building shell is also convincing by amazing characteristics thanks to the HT coating (HT = Hydrophilic Tiles, i.e. “water-loving“ tiles). This innovative solution is durably baked onto the glaze at high temperature already in the factory and lends facade ceramics of Agrob Buchtal remarkable properties:
Rain water does not roll off in big drops but forms a thin film thanks to the hydrophilic surface, which infiltrates and detaches dirt. Due to this “self-washing effect“, every shower becomes a cleaning process free of charge. This not only ensures a perfect look but also permits to reduce costs.
In addition, HT has an antibacterial effect: following the principle of the photocatalysis, light effects a reaction by which activated oxygen is produced, which decomposes microorganisms such as bacteria, fungi or moss without using any chemical products and inhibits their renewed formation. In this way, the problem of the growth of algae or the “greening” of facades can be efficiently counteracted without fungicidal substances.
Last but not least, similar to a forest of deciduous trees, the coating decomposes air pollutants such as, for example, the exhaust fumes of industry and cars. Thus, the Pretoria Tower acts as “vertical urban forest“ – an aspect which is of particular value above all in densely populated city centres like in this case. During the renovation works, the inhabitants of Pretoria were visually informed about this extraordinary quality by a mega-poster with the word “breathe“.
The photocatalytic effects of HT are not used up but are permanently reactivated by light. Thus, they are always effective – a whole tile life long.
The analysis of Boogertman + Partners already mentioned finally states: “The renovation retains the building’s character of a historic monument by integrating key elements, preserving the central design principles of the original concept and, at the same time, increases the value of the facade thanks to a modern, safe solution“ – a conclusion which one can absolutely confirm.
AGROB BUCHTAL, www.agrob-buchtal.de