Baroque shell, modern core

Project:
Humboldt Forum in the rebuilt Berlin City Palace
www.humboldtforum.org

Architecture:
Franco Stella Berliner Schloss-Humboldtforum-Projektgemeinschaft 
www.francostella.eu.

Products: 

  • KEIM Soldalit
  • KEIM Soldalit-Fixativ
  • KEIM Restauro-Lasur 
  • KEIM Restauro-Fixativ
  • KEIM Optil

Photos: 
Stephan Falk 

City Palace in Berlin

On the 16th of December 2020, the reconstruction of the Berlin City Palace was opened - initially virtually due to the pandemic. Used as the Humboldt Forum, it houses modern exhibition rooms behind baroque façades that were created as a precise reconstruction. The planners relied on KEIM products for the coloured sections, but how do you determine the historical colour scheme of a building whose last remains were blown up 70 years ago?

With the reconstruction of the Berlin Palace, a piece of urban repair in the heart of Berlin is now completed. The palace was the starting point for the city's most famous architectural ensemble: Zeughaus (armoury), Cathedral, Neue Wache (new guardhouse), Humboldt University and the Museum Island - they all related to the palace. And of all things, this original building block had been missing since it was blown up in 1950 after severe war damage. The reconstruction now closes the urban gap. Consequently, the reconstruction of the historical appearance is limited to the façades, while the interior completely meets today's requirements of a space for modern exhibitions and events.
The Italian architect Franco Stella, who won the international planning competition for the reconstruction in 2008, took appropriate liberties to make some innovations. For example, he realised the Spree wing, which is less decisive for the ensemble effect, in today's formal language. And he designed an openly accessible passage that leads right through the palace. It is an expression of the building's new use: instead of being the imperial residence and seat of government, it now serves as a public place of encounter and education under the name "Humboldt Forum". 
It houses 43,000 square metres of event and exhibition space, including for the Stadtmuseum Berlin, the Museum of Asian Art, the Ethnological Museum, Humboldt University and for a permanent exhibition about the history of the site by the Humboldt Forum Foundation.

Detailed work on the facades
The reconstruction of the building envelope refers to its condition before the Second World War. At that time, the palace essentially displayed the façades that had been created according to designs by the master builder Andreas Schlüter. From 1699 onwards, he had turned the Renaissance palace into a magnificent Baroque residence based on Italian models.
The exterior walls of the current reconstruction have a considerable cross-section of more than 1 m. A load-bearing concrete wall on the inside (30 - 50 cm) is followed by an insulation layer (12 cm) and then again the reconstructed facade layer (64 cm). It is mainly composed of bricks and sculptural stone carvings made of sandstone. The outer finish of the brick surfaces is a lime-cement plaster (2 cm). Altogether, craftsmen made 22,000 sandstone workpieces, 2,828 figurative motifs and 513 windows according to historical models. The sandstone used comes from various quarries in Saxony and Silesia.

Looking for the right colour shade
But what colour should the reconstructed render facades be? Original building fabric was just as non-existent as the original building documents. So which sources should be consulted instead? Early pictorial representations were etchings made by Johann David Schleuen around 1750, but they were not coloured. Only paintings by the Biedermeier artist Eduard Gärtner from the beginning of the 19th century show a yellowish castle, but at that time the building was already over 100 years old. A comparative reconstruction also proved difficult: The facades of the rococo Sanssouci Palace in Potsdam, for example, are yellow, while the baroque Armoury opposite the Berlin Palace is painted pink. Finally, a preserved piece of plaster was found that had been stored in Charlottenburg Palace. This original find, about the size of a hand, shows a quince yellow tone and could be dated to 1820 by a restorer's expert opinion. According to today's knowledge, this is the earliest confirmed colouring, so that this tone was chosen. It also harmonises with the sandstone of the columns, cornices, window jambs and balustrades.

Committed to the original 
A lot of attention was paid to the coating process to achieve a look that was as close as possible to a historical appearance. Instead of the dispersion paints commonly used today, purely mineral products from KEIM were used. KEIM Soldalit was first applied to the lime-cement plaster as a base colour. To ensure that this layer did not appear too opaque, but slightly cloudy, the painters diluted the paint 1:1 with KEIM Soldalit-Fixativ. In order to achieve a depth effect at the same time, KEIM Restauro-Lasur, also diluted, was then applied in two work steps - as in the past with a brush, so that the façades show the craftsman's process of creation. A slightly different shade of yellow was used on the projecting plaster surfaces than on the recessed surfaces. This fine differentiation emphasises the plasticity of the façades.

Discovery in the basement
Before construction began, archaeological excavations took place on the site of the former castle. Remains of the cellar and catacombs came to light, as well as remains of an old monastery that had once stood there. The wall sections were secured, restored and covered with a concrete ceiling. Today, visitors can dive into the past and see a separate exhibition about the history of the place. The ceiling was given a subtle black-grey coat with KEIM Optil, which underlines the original components and exhibits in terms of design.

Reason for confidence
In recent times, some large-scale projects have greatly exceeded their costs. The Elbe Philharmonic Hall in Hamburg, for example, achieved a certain notoriety with an increase of 250 per cent, but the Berlin airport with 300 per cent also raised the question of whether highly complex large construction projects can still be reliably planned at all. The Berlin City Palace, on the other hand, remained almost on target: With 644 instead of the planned 595 million euros, the additional costs were moderate. Hans-Dieter Hegner, the Humboldt Forum board member responsible for construction, explains: "This increase is mainly due to the fact that the enormous general increases in construction prices were not foreseen when the 2011 budget was drawn up". In any case, the reconstruction of the palace shows one thing: large-scale projects can still be realised in Germany in such a way that the cost limits are largely adhered to.

Text: KEIMFARBEN GmbH

More international reference projects