Brick masterclass

Developer Helical Bar wanted to build two office buildings on a site in the middle of all this. The brief to architect Hamilton Associates was for large, open-plan layouts; their task was to slot them seamlessly into this architectural clutter. It was a challenge made all the more difficult because one office would have to incorporate the listed brick facade of the old West London Hospital.

Despite the location, the developer was looking for high specification offices to attract prestigious tenants. The architect's solution was a microcosm of the area's mixed styles: 200 Hammersmith Road is a glazed, five-storey 6000 m2 building with trim, four-storey high brick columns and crisp stone detailing. The adjoining four-storey Saunders building hides behind its historic facade.

Number 200: a hand-made building
What would merge the two buildings into the urban fabric would be their use of masonry, so getting the design and construction of the brickwork right was crucial. However, each building had to be tackled differently. The most prominent feature of Number 200 was the brick columns that rise from the pavement to the fourth floor at every bay. Their prominent position meant that careful architectural detailing was essential if the developer's quality standards were to be meet. The 800 mm radius columns are subdivided by reconstituted stone circular bands at each floor level; the same reconstituted stone is also used to construct the facade's lintels and coping stones.

Because the detailing of the columns was so critical, the architect called in brickwork specialist James and Taylor to produce detailed designs for the masonry and manage the procurement and production processes. The specialist also assisted in the selection and procurement of the brick, on the basis that it had the knowledge to select a type with manufacturing tolerances tight enough to keep the mortar joints a constant width. It even had to design one-off brick shapes to ensure that the joints ran in perfectly straight lines. Managing director Bob James claims that his company saved the architect from having to sift through hundreds of suppliers to find the right brick.

What James and Taylor chose was Williamson Cliff's Stamford Stone Brown-Grey, which James describes as "a wonderful brick with a unique appearance". It is a handmade brick, with a fine texture, sharp edges and no "smiles" – the brick-fancier's term for a curved darker patch – and was chosen because it complemented the traditional London bricks in the adjacent listed facade. Of critical importance was the compatibility of the standard facings and the specially shaped bricks for which this Williamson Cliff type is renowned.

Richard Pendlebury, associate director of Hamilton, is quick to praise James and Taylor's attention to detail, but he wonders how it conjured up so many expensive specials. James says 100 shapes were necessary to achieve consistent mortar joints on the columns and crisp vertical lines through the perpends. "The difficulty was maintaining the bonding patterns through the columns," says James (see the annotated cross-section, below, which shows the architect's original drawing).

To ensure that the bonding pattern was uninterrupted, E E the architect gave careful consideration to the location of expansion joints. To minimise the use of expensive mastic sealant, the subcontractor inserts a compressable polyethylene backing strip in these before using a gun to squeeze in mastic to a depth of only 5-6 mm. The joints are in part disguised by the Portland mastic, which, contrary to its name, is actually closer to the colour of the bricks than the stone.

Pendlebury was worried that the project's budget would not stretch to employing a top brick contactor, which could have jeopardised the masonry finishes. The project's main contractor, Try Construction, warned Pendlebury that if he "went cheap", there would be a huge snagging list. In the event, the foundations came in for less than expected and so there was enough money to hire Irvine Whitlock, which Pendlebury says is one of the best bricklayers in London. Alastair Krull, Try's project co-ordinator, believes the selection of Irvine Whitlock was crucial to the styling of the buildings. "It was a tremendously difficult job. It wasn't a case of choosing any old subbie," he says.

Specialist stonework firm Con-Tech cast the reconstituted stonework for the facade details – a joint decision by Hamilton and Try. Con-Tech is unusual in that it uses hand-produced drawings to get greater accuracy, as ill-fitting stone features can take up to six weeks to recast. To make doubly sure that this did not happen, Irvine Whitlock put a cutting machine on site. The on-site cutting meant that Con-Tech and Irvine Whitlock were able to use the 5 mm stone joints that Pendlebury insisted on. "Portland stone looks much better with 5 mm joints. Ten millimetres looks awful and too modern."

The Saunders building: Victoriana renewed
The first decision the architect faced on the Saunders building was how to restore its retained Victorian facade. Pendlebury says his practice didn't have the expertise to detail the work required. "Unless you're an expert on Victorian facades, it would have been difficult to write a specification for this building," he says.

Instead, the architect paid masonry restoration specialist Szorelmey £5000 to make a survey. "The specialist listed 120 things that needed to be done to restore the facade, which made it easy for us to come up with an accurate brief," says Pendlebury. "This type of report gives us a good starting point for a relatively small cost, and clients really like it because they know what they're paying for."

Although Szorelmey undertook the survey, it was another masonry specialist, Stonewest, that successfully bid for the work. It had an uncanny knowledge of what buildings had been demolished recently and which were due to be knocked down, so were able to find a match for the imperial sized bricks that were to be replaced. As well as restoring the facade, Hamilton also had to bring the wall up to modern insulation standards using Kingspan's Thermawall insulation panels and Hanson's 140 mm blocks (see "Not just a pretty facade", overleaf).

To match the bricks of Number 200, the architect selected Ambion's Wealden London Multistock. Again, Pendlebury looked to James and Taylor for advice on the choice. This brick was specified because it was handmade and had a textured finish that was not too crisp, but had sharp corners to complement the more expensive bricks on the main facades of Number 200. And the fact that the bricks were used on the rear elevation meant that Pendlebury could get away with specifying bricks that were £270 per 1000 cheaper.

Pendlebury chose Yellow L mortar after inspecting a range of sample brick panels. Some of these also featured stonework and window sections to give the architect an accurate impression of the final facades.

Try's Krull says the skill of Irvine Whitlock was crucial in making the cheaper bricks match the character of the Victorian facade. "Give an ordinary brickie a medium quality brick and he'll make a bad job of it," he says. According to Krull the contractor maintained tight quality control over the bricks it used, rejecting bricks with slight imperfections and making sure those with smiles were all laid the right way. Like the retained facade, the rear wall was a standard brick-blockwork cavity construction

that used Hanson's blocks, Kingspan's insulation and Anchon's stainless steel wall ties.

Hansom's 140 mm concrete blocks were selected because of the large floor-to-ceiling heights of the Saunders building. "If you build 3 m high with 100 mm blocks and punch the wall, the whole thing wobbles," says Pendlebury. Irvine Whitlock installed the blockwork first to seal the building against the weather and allow work to begin on the inside of the building. The cavity width was 100 mm with 45 mm of Kingspan Thermawall, leaving a 55 mm clear cavity.

On the new facade at the rear of the Saunders building, stainless steel shelf angles were used every two floors to secure the brickwork to the steel frame. The bricks were tied to blockwork walls, which sat on concrete floors of the steel frame structure. Mastic joints were used on the storeys where the shelf angles were used and were masked by a band of Portland stone.

The project is finished, and Helical Bar has two brick office buildings that meet planning requirements, with distinct but complementary facades. And guess which of the two cutting edge high-tech company Sony-Ericsson chose to rent? The one with the Victorian facade …