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Made in Chailey

Clay Technology magazine
15 Dec 2014

Melanie Rutherford takes a tour of Ibstock Brick’s Chailey factory in East Sussex with site manager Damian Descombes, who explains how its traditional – and now rare – clamp-fired brickmaking method produces a unique range of colours and finishes. 

The well known method of firing bricks in kilns dates back more than 8,000 years. Prior to that, a much lesser known firing process enabled mass production. Clamp firing, the process of stacking bricks over a bed of fuel and then setting it alight, is an increasingly rare method unfamiliar to many brickmakers today. Clamp firing is now practised at only a few sites, all located in the south of England. Ibstock Brick Ltd’s Chailey site, in East Sussex, is one of the smallest factories keeping the tradition alive, producing around 12 million bricks a year by this unique process.

The initial stages of brickmaking are the same as that for producing kiln-fired bricks. Once a year, clay is extracted from Chailey’s main quarry and then brought to the factory and stored in the stockpile area. Damian Descombes, Factory Manager at Chailey, explains, ‘It takes about two weeks to move around 14,000m3 of clay. The stockpile is built into 17 different layers for use the following year. At the moment, we use three different types of clay in the recipe. Some clays are difficult to dry and you can get shape and cracking problems, so we need to make sure we get the recipe blend exactly right.’

The clay is then processed and demoulded as usual, and then dried to produce a regular unfired brick. It is during the hard-firing and vitrification procedure that a more unusual process begins. Instead of feeding bricks through a tunnel kiln, the unfired products are stacked in what is known as a clamp. Descombes explains, ‘A clamp structure is effectively a carefully constructed stack of bricks. We then set fire to that structure until the bricks are hard enough to use for construction.’

Traditionally, a clamp structure is built outdoors underneath a large shed over lanes of gas burners – or another fuel, such as coke or wood. On ignition, the fuel transfers through the clamp, reaching temperatures of more than 1,000°C.

Once all the fuel has burnt out and the structure has cooled down, the hardended bricks are individually hand-sorted for colour and quality.

The main difference compared with modern kiln-firing methods lies in the consistency of the finished product. ‘It’s not quite like a tunnel kiln, where you can control the atmosphere inside the same as you would an oven,’ says Descombes. ‘With a clamp, we’re just placing bricks on the floor outside under a shed – we can’t control the atmosphere from outside. Each clamp carries around 800,000 bricks, but sometimes when we are firing and the wind blows hard in the wrong direction, it’s going to blow the heat away from certain parts of the clamp. This means that bricks on one side of the clamp will not get fired as hard as those on the opposite side. The reduced temperature also means the colour will be slightly different.’ Any bricks that are slightly over-fired may stick to the ones next to them, producing heavy ‘spotting’ – while this would normally be undesirable, this helps to give clamp-fired bricks their unique appearance that potentially allows a house to look 30 years old within a matter of weeks.

It is this characteristic that sees these bricks in consistent demand from architects and specifiers wanting a very traditional or old-looking sustainable building material. ‘You’re going to get different characteristics and colour from every single brick – each will be slightly different to the one sitting next to it and the one above it,’ says Descombes. ‘That is, in some respects, what gives it its beauty. If you wanted a plain colour every time, you wouldn’t necessarily come to a clamp firing factory.’

Setting of the unfired bricks into the clamp structure is key. Descombes explains, ‘The bricks have to be certain widths apart, so we use special boards to ensure they are as level and straight as possible, with thin gaps between each brick to allow air and heat transfer.’ This calls for a significant amount of skill and experience from Chailey’s 34-strong team, with different spacings required for different colour stocks. ‘You need that air to give the bricks their colour development, otherwise they will overburn and all you’ll get back are dark bricks. Reds tend to burn off at 1,000–1,030°C – any less and they’ll come out orange. So you need to increase the amount of fuel on a red sanded brick to give the product a better colour.’

Problems can also occur should the clamp structure not be stable. Bricks falling into the tunnels can cause the products to melt, while an open clamp construction would allow excess air to circulate in certain areas, creating problems throughout the entire clamp. To mitigate these issues, Chailey’s clamps are covered with an extra layer of hardened bricks, to keep as much heat inside the clamp as possible. For this, it imports special white refractory bricks measuring around 100mm thick – though with 33,000 required to cover one clamp, recycled waste bricks also prove useful for the job. ‘We can use bricks that haven’t fired properly from previous clamps, and keep using them until they break,’ says Descombes. ‘The refractory bricks are a lot better at insulating and maintaining consistency, but they are not as strong and tend to break more easily.’

Coat of many colours

Despite every brick leaving the Chailey site containing the same raw materials, the factory produces a wide range of colours, textures and finishes. Descombes explains, ‘One brick can have a consistent red exterior, another a darker red with a lot of spotting on it, some half-and-half with a cigar shape on the inside, and some spotting within that cigar shape.’ The factory’s signature brick is its Chailey Stock – a traditional red base colour, but each varying in colour and finish. 

The Chailey Rustic is another red, but slightly lighter than the Stock – however, both types are produced from the same clamp.

The main reason for this is that a clamp is a two-tier structure. More air circulates at the bottom of the clamp where fire holes have been created – these cool the bricks at the base, producing the lightest colours. Conversely, the top half of the clamp has a higher and more consistent heat, producing darker bricks with less colour variation. These bricks at the top half of the clamp produce the best yields and are selected for the Stock range, while the lighter reds from the bottom half form the Rustic colour set.

But Chailey is not limited to producing red multi-coloured bricks. Through clever use of additives and coatings, a whole range of coloured bricks are now made, from yellow to purple to black. ‘We have always tried to disprove the myth that you only get certain types of brick from a clamp,’ says Descombes. While the majority of colours are produced using different sands on the outside surface – a consistent and relatively simple process – some prove trickier to make.

The Cooksbridge Yellow is an example of this – a sought-after colour but one that is difficult to produce from a clamp. ‘To produce a yellow brick, we have to add chalk to the surface, which reacts slightly differently in the firing process under certain temperatures,’ says Descombes. ‘Overheat the bricks and they will literally fuse together, so you get a lot of waste or black sticking. At the other end of the scale, with not enough heat, you struggle to maintain the yellow colour and the product tends to go an off-pink. Stained coloured products can prove more difficult to sustain high yields.’

Black is another colour growing in popularity but tricky to produce in consistent yields. ‘You can, of course, get a black brick by over-firing or using too much fuel, but if you do it that way you’re doing something wrong,’ says Descombes. ‘Overheating produces too much sticking, so you get chips and cracks when you try to separate bricks, and too much heat will also cause the brick to deform. We produce a black brick using surface stains and various additives to make sure we can achieve a clean product.’ However, with the cooler bottom half of the clamp not able to produce a true black colour, like the yellow stock, many of the bricks can go to waste.

Descombes explains that typical waste from a clamp can be as high as 25%, ‘but Chailey’s waste is currently much lower, due to its stringent quality regimes and attention to detail. Although that’s still not as efficient as kiln-firing – most brick manufacturers won’t use clamps because of that. In the modern era, it is harder and harder for this type of process to compete with more modern and efficient processes. Our battle going forward will always be to keep our efficiency high and waste as low as possible, while still trying to manufacture a product with a unique traditional character and at a low cost.’

Damian Descombes: a career in bricks

Damian Descombes began his career in a very different field to bricks. He studied as a carpenter after leaving school, before deciding on a career in market trading. It was while waiting for his trader’s license to come through that Descombes came to work at Ibstock’s Chailey site. Having learnt several jobs within the site over a number of years, he was promoted to his current role as the Factory Manager.

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