Ketley Brick – Clay Pavers & Bricks
I was recently invited to Ketley Brick’s headquarters in Dudley to see how they make their famous clay brick pavers and other products. My great tour guide, Alastair, showed me around the factory.
Ketley Bricks was founded in 1805. In the early 1900s, R S Davenhill, a mining engineer by trade, joined forces with Mr Hinton and Mr Perry to build and design a whole new plant and manufacturing system. Despite two world wars and a major fire in 1971, Ketley is still going strong today and is still run by the Davenhill family.
As with any paving product, especially clay pavers, it is all about the raw material. In this instance, the Etruria Marl clay is a seam of clay that starts in North Staffordshire and runs all the way down through the West Midlands to Wrexham in North Wales. Originally, the Ketley quarry was on-site, but their new quarry is in Cannock, only 11 miles away. The clay is also mixed with locally sourced naturally occurring sand.
So the big question is, what are the properties of Etruria Marl that set it apart from other clays? Etruria Marl has a very high iron content, low lime content, low in impurities, has an ultra fine particle size, high plasticity when wet, and a silica content, producing durable, low water absorption, high compressive strength Class A clay pavers and bricks that make Ketley bricks a superior product. Etruria marl clay also has the lowest amount of embodied carbon, which is great from a sustainable perspective. The clay is extracted from the quarry and stockpiled in thick layers for 6 months. The stockpile enables the effective mixing of the clay that may have some variation in the mineralogy when extracted from different parts of the quarry.
The clay extraction is managed carefully, and its composition is monitored and tweaked/quality checked onsite if necessary.
The factory at Dudley receives approximately 160 tons per day. It is stored in a large covered bay area, ready to be put through a series of hoppers/shakers that break the clay down to particle sizes of 1.5mm for bricks and pavers or 1mm for roofing and tile products. The fine clay is then carried on conveyor belts to the extruder. Extrusion is where moisture is added to the clay and pushed through a “dye” of a particular shape, brick or tile. The extrusion process is similar to squeezing toothpaste out of a tube.
The bricks are then cut to shape, and a pattern can then be pressed into the wet clay brick. Although the most common surface patterns are diamond, two-panel, eight-panel, and star patterns, often referred to as the Star of Staffordshire, bespoke patterns can also be made to order.
The clay pavers are then stacked on pallets with a layer of locally sourced sand between each layer to help prevent them from sticking together. The wet bricks are put into large controlled drying chambers where the heat and humidity are closely monitored. The drying chambers are partially heated using recycled heat from the kilns, making it an energy-efficient process. The bricks are dried for a minimum of 3 days in this controlled atmosphere. Slow drying and moisture reduction are essential to reduce the chances of cracking and warping deformation when fired in the kilns.
The bricks are then stacked on airflow bricks or “saggers” and fired in the kilns for around 30 hours at 1180 degrees Celsius. This is where the magic happens! Ketley use the traditional age old method of regulating the kiln atmosphere to produce their renowned Staffordshire colours. A reduced oxygen atmosphere introduced at the peak of the firing cycle forces a reaction with the iron in clay, and fixing the colour blue into the bricks. An alternative modern way to mimic this effect involves using applied surface stains which is far less effective than the reduced oxygen atmosphere method, but it is cheaper. Red Ketley bricks are fired in an oxidising atmosphere (where oxygen is present).
The bricks are allowed to cool down slowly while still in the kiln for 24 hours and are then quality-checked. The wastage is only small, mainly due to cracks or warping. These defective bricks are crushed and used to stabilise access roads in the clay quarry also local farmers often use them on their field tracks, too. It’s worth noting that there is no waste until the firing process; it all gets recycled. Most factory workers live within 2-3 miles of the premises, and many families have worked there for generations.
Waste brick-wise Ketley have also been experimenting with a terrazzo style paving slab, but this is still in its infancy stages.
Where the fired bricks have colouration outside of the tolerances, they become a “Multi Blend” concession brick, sold slightly cheaper, which I have to say I actually prefer, especially for garden projects.
Ketley have now started making Dutch-inspired thin-set clay pavers and they are the only british maufacturer to be making pavers in this size format. The Ketley paver colour range is a Staffordshire Red, Brown Brindle and Blue. Their brown brindle colour has more tonal variation which is achieved by cleverly stacking the bricks in the kilns and partially reducing the atmosphere, so that some of the pavers have a lighter brindle“hearting” which gives a unique, rich, clay colour.
Meeting Class A brick requirements with a water absorption of less than 4.5% and compressive strength of greater than 125N/mm2, it is easy see why these products are capable of lasting in excess of 100 years and are still seen on the streets of the UK and as well as still being available in reclamation yards.
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