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The Darwin Cocoon

Natural History Museum Darwin Centre ‘cocoon’, London

Client: Natural History Museum
Architect: C. F. Møller
Main Contractor: HBG Construction

The Darwin Centre cocoon creates a new architectural icon for the capital, ground-breaking in scale and breath-taking in its originality and creative brilliance.

The design features a vast free-standing structure taking the form of an enormous cocoon within a glass atrium. The eight storey high cocoon houses a unique collection of 17 million insects and 3 million plants collected over the last 300 years by scientists including Charles Darwin, Alfred Russel Wallace and Sir Hans Sloane. The building completes the Museum’s life science complex, the Darwin Centre, following the first phase opened in 2002.

Design Team

The response of the architectural design team at C.F. Møller, lead by partner Anna Maria Indrio, was to create an engaging image reminiscent of an essentially organic form. The surface and texture also needed to reflect this, so the subtle sheen of the ivory coloured Armourcoat plaster was chosen. With an intersecting network of ‘silk threads’ that criss-cross the cocoon, the surface allows for movement and provides a visual framework for openings and niches. Armourcoat was specified to devise a unique creative solution combining both the insulation and the final decorative layers. The cocoon performs a genuinely protective job providing thermal mass to inhibit any fluctuations to the internal temperature – essential for the museum’s treasured specimens. The structure also houses state-of-the-art laboratories for 250 international scientists and an interactive visitor exhibition.


Construction

A sixty-five metre long skeletal structure was built by sprayed concrete specialist Shotcrete – the first above ground sprayed concrete structural element in the world. Expanded metal mesh was fitted to the steel re-bar framework and a 250mm thick layer of concrete was spray applied to create a 3,500 m2 raw concrete surface. Armourcoat then applied a resin modified render to the structure to minimize localized variations to the surface, before the polystyrene insulation layer was fixed. Using Dryvit Genesis adhesive and over 16,000 Hilti insulation fasteners, a 50mm polystyrene layer was fitted to the entire surface of the cocoon then covered with a layer of reinforcing mesh bedded into Dryvit Genesis basecoat. 

To create the silk threads wrapping the structure, a special cutting machine was devised which could cut an accurate slot and create the individual 340 panels which make up the cocoon surface. A total of 5.6km of edge bead was then fitted before Armourcoat’s unique AntiCrack substrate preparation system was applied. AntiCrack is a polymer and fibre modified gypsum skim-coat plaster which creates a first class substrate, keeping the Armourcoat plaster layer in peak condition. Two layers of Armourcoat keycoat were applied prior to the application of the final finish. The finished effect of a giant silk cocoon was achieved using ivory coloured Armourcoat Armuralia polished plaster - an exquisite, smooth finish with subtle tonal variations.

The cocoon is a milestone achievement, a unique design and technical solution befitting the historic and social reference of the Natural History Museum. This also is a stunning example of the type of commercial projects now undertaken by Armourcoat, celebrating twenty-five years of creative excellence in 2009.