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Modern marriage

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Malcolm Barnett reflects on a successful union of brick and glass

The new National Lottery-funded World of Glass museum houses the relocation of both Pilkington's and the St Helens' glass industry Malcolm Barnett exhibitions. Its site can be seen as the birthplace of St Helens' industrial revolution; coal has been mined here since the sixteenth century and as a result the area has attracted all manner of furnace-based industries, including glass.

Glass, the quintessential material of the Modern movement, gives buildings their transparency, lightness, and crisp machine-age aesthetic. The major advances in glass manufacture of recent years further increase its seductive appeal. Brick, on the other hand, has at least two millennia of construction tradition behind it. What place then does brick have in the design and construction of a twenty-first century museum of glass? Part of the answer lies in the history of glass manufacture. Early coal-fired glass-blowing kilns were tall, conical brick structures, so shaped for the strong updraught that was essential in order for fuel to burn efficiently.

The museum

The new museum is made up from four main structural elements. These comprise a brick cone structure, and what can best be described as two large brick boxes, all connected by a large planar-glazed circulation area. The brick structures have no windows while the walls of the circulation area are completely made of glass, in what the architect describes as a 'black boxes, white light' concept.

Solar gain is controlled on the south-east elevation by a 6.9m high free-standing glass 'armadillo' wall, set in front of the main glazing.

This wall is designed with overlapping panels that allow independent removal and reinstallation so it can be used for testing new types of glass as they are developed. On the south-west elevation, a glass canopy of fritted glass provides solar shading. All other glass is of low emissivity to reduce heat loss.

The brick structures

The brick cone forms the entrance hall to the museum. Measuring 16.1m high, with a 6.6m radius at the base tapering to 4.6m at the top, it is constructed from solid one-and-a-half brickthick brickwork (327mm) in English bond, inclined at a 15degrees angle.

Designed as a sheltered outdoor space, it is unheated, reverberant and damp. Solid brickwork set at this angle inevitably lets in a certain amount of water in wet weather. As a result, when passing through this space one gets the undeniable feeling of passing through another period in time and can imagine that this structure was actually once a glass-blowing kiln.

From the cone a short glazed link takes visitors into the central circulation area, which also contains the ticket desk, souvenir shop, display area and cafeteria.

The two-storey brick boxes house the main museum exhibits, including an area where demonstrations of glass-blowing are held. These massive structures are constructed with loadbearing brick fin walls, with concrete-block inner leaves. The 13m high fin walls themselves are one brick thick (215mm), in Flemish bond, and are battered at 2.5degrees. The fins, at 1.2m centres, are one-and-a-half bricks thick (327mm) and 1.2m deep at the base, tapering to about 600mm at roof level.

Lime mortar

One of the main characteristics of the brickwork is the exclusive use of natural hydraulic lime mortar, that is, mortar containing no Portland cement but depending on hydraulic lime as a binder. The designers considered that the thick, load-bearing nature of the brickwork, combined with the autogenous healing properties of lime mortar, justified the construction of these structures without movement joints.

Project architect Paul Green is quick to point out, however, that lime mortar should not be viewed as a straight substitute for a Portland cement based mortar. In the absence of design data for natural hydraulic lime mortar, except as provided by individual lime manufacturers for their own products, specialist advice was needed on the correct specification of the lime mortar and bricks.

There is also a general lack of experience and understanding on the part of both specifiers and site operatives of the special requirements of lime mortars in respect of specification, storage, protection, laying and curing times. The lime used in this case was a St Astier NHL5. Joints were flush finished with a wooden float.

Water penetration

At design stage sample panels of the cone structure walls were constructed and subjected to both structural and water-penetration tests.

These tests indicated that some water penetration of this inclined brickwork was likely to occur in conditions of extreme rainfall. In order to minimise the degree of rain penetration, especially high standards of workmanship were required from the bricklayers, particularly in filling all the cross joints with mortar. This was achieved by adopting a policy of continuous visual supervision of the work in progress.

This is a building in which the modern technology of structural glazing and fritted glass, in combination with traditional loadbearing brickwork and historic forms, is used to great effect. As one rounds the corner in Chalon Street, the first sight of the cone - sudden and dramatic - is breathtaking: World of Glass brings together old and new, void and mass, solid and transparency in a striking and convincing way.

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