Underneath the arches - Rebuilding St Pancras station

Clay Technology magazine
,
1 Feb 2007
The long arcade at St Pancras station, London

The persistent rumour concerning the British construction industry suggests that the sector no longer has the necessary craft skills to handle difficult large-scale projects with intricate brickwork detailing. The two UK companies that produced the hand-cut arches at St Pancras Station in London would, however, disagree. Brick maker Bulmer Brick & Tile Ltd (BBT), along with Bulmer Brick Cutting, produced the fully washed clay blocks and hand-cut Gothic arches for the rebuild of the west elevation of St Pancras station.

Clay choice

The main contractor had to choose a brick supplier who could match the original soft red rubbers for colour and texture and find a brick cutter with the skills to achieve the tolerances and consistency required. There were doubts that BBT could supply the quantity and quality of blocks within the time frame, and that the cutting shop could consistently cut and supply 22,000 pieces to the required accuracy to meet the build schedule.

A major factor in resolving the problem was the clay itself. When St Pancras was originally built in the early 1870s it was the largest rubbed and gauged brickwork project in the world, consuming vast quantities of facing bricks (supplied from the Midlands) and all of the UK’s stock of fully washed rubbing blocks. One of the suppliers who were asked to contribute to the modern work was Allens of Ballingdon in Suffolk. The branch of the clay seam that Allens holds is identical to the seam of clay worked in the next valley by BBT. The straight-line distance between the sites is less than two miles, thus the material sold itself.

Meanwhile, the Bulmer cutting shop team planned every stage of production – what to do and how to deliver. As a result, the order was won.

Accuracy and consistency

The second challenge was in achieving accuracy and consistency on the hand-cut products. There were only three profiles to manufacture, but the difficulty was that there were 8,000 of them to be made.

As in many crafts, the skill in creating a quality product is in the preparation of the material. Traditionally, the raw block would be rubbed on a circular flat York stone slab, maybe 18 inches in diameter. This reduces the bed to a flat surface. The block would be turned through 90º and its face rubbed to an exact perpendicular and checked with a square. Today, this process of ‘bedding and squaring’ is simplified with mechanical sanders.

Hand cutting involves a wooden bow saw with a blade of thin twisted wire and lots of elbow grease – a job not for the faint-hearted. The bow saw is guided by the brick-cutter over a pair of timber profile templates. Although the timber wears out and changes shape, a harder template material would ruin the soft blade. The solution is to reverse the templates every 25 cuts and change them every 50 cuts.

Swapping and replacing templates is only a valid exercise if all of those for a particular shape are exactly the same. This means 320 templates are required with over 100 copies of each shape.

This is no mean feat – a pattern maker would charge a large fee and not achieve the accuracy consistently. Bulmer’s solution was to borrow methods from another industry. The company asked an organisation that normally works within the packaging industry to laser cut 15mm birch ply templates from computer-aided design (CAD) drawings supplied by the client. Thus the problem was solved with computerised repetition.

Perfect results

When St Pancras was originally constructed, everything was hand cut and rubbed. Looking closely at the work, it is clear that this was done to differing levels of accuracy. The modern brief was to achieve perfect results over the entire run of arches. This would be impossible and uneconomic without the use of diamond-tipped circular brick saws.

The basic EDW Major masonry cutting sawbench made by Norton Clipper is used all over the world and is standard site equipment. Bulmer Brick Cutting has four, all with three phase motors and adapted for dry cutting with dust extraction systems fitted.

However, the longer the clipper is used, the less accurate it becomes. As the hard nylon trolley wheels wear on the grit and dust, the sideway travel of the trolley increases, making the long cuts inaccurate. The specification was to produce tapered cuts of 0.5mm over 115mm and 1mm tapers over 229mm – this was not possible with the basic design of the machine.

The trolley was redesigned to run on rails with spring-loaded wheels constantly pushing it onto the ‘true’ guide rail. This was set with an engineer’s clock gauge to be perfectly parallel with the blade.

The nylon wheels were replaced with new brass wheels with ‘O’-ring tyres. These wear more slowly and replacing the tyres costs just a few pence.

The cutting team now had an accurate saw that ran in a straight line, however, they still had to set up each cut. How could a tilting table be set to cut a 0.5mm taper? The answer was to ask the laser company to cut a series of templates exactly to the taper, length and height required. Then, with a little practice, the brick masons could accurately set the tilting tables from the plywood guides before replacing the wood with the brick to be cut.

 

The next concern was how to check the work and guarantee the accuracy. The contractor required a quality control document with each delivery.

Again the laser company were of assistance. They produced negatives of all the tapers to slide neatly over the finished brick type (over 84 variations on the basic three shapes) proving that the taper was correct.

Boxed delivery

It is not easy to safely deliver to site over 20,000 pieces in the correct order, to lay straight out of the box. Therefore, the packing trays were designed and purpose made for the project. They had to be easily manhandled, strong enough to protect, cheap to produce and stackable, while creating only a small footprint on site.

Delivery also presented a challenge. One option would have been to deliver each arch as separate trays of each brick type – 25 x type one, 30 x type two and so on. This would have created disorder on site, and material would have been lost and damaged.

A system was designed that could be followed without the need for onsite training or reference to complicated drawings. This moved from tray one through to tray 13 and from the blue end (the jamb) to the red end (the key) on every tray. On the larger arches, 13 trays of 16 bricks represented half an arch. Each arch therefore had two pallets per arch, one left hand side, one right. The pallets arrived with a diagram clearly showing each brick (drawn to scale), numbered in position in its tray. This worked perfectly. Bulmer Brick Cutting also packed huge pallet covers with each delivery to allow used trays to be covered and collected for reuse.

There were also concerns regarding tolerances of the cut stone, drying problems in rubber manufacture, sand folds, sand grain sizes, clay blends and air holes. All were addressed and solved.

At the 2006 Brick Awards organised last November by the Brick Development Association, this project was awarded the Best Craftsmanship Award. The bricklayer, Irvine Whitlock, scooped The Specialist Brickwork Contractor of the Year (see Clay Technology, December/January 2007 p2-3).

 

Further information:

Bulmer Brick Cutting was established in 1993 and employs 11 staff. The company services a wide range of customers with a large product list including cut and bonded brick specials, as well as the more traditional arches and hand-cut special bricks. For further information, contact Colin Pinnegar, tel: +44 (0)1787 269132, email: colin@brickcutters.com.