The first steps out onto the dome of the beehive kiln are a bit unnerving, with only a thin shell of tightly-fitted bricks supporting a small group of us above the void below. Domes structurally similar to this have been around since antiquity – many notable examples still survive – but it’s reassuring to know that scaffolding inside the kiln will prevent a painful and possibly career-ending collapse.
Kiln No. 2, one of four historic beehive downdraft kilns at Medalta Potteries, is a circular drum roughly ten metres in diameter with brick exterior walls surmounted by the dome and a tall central stack. Encircling the walls are wide adjustable bands of corroding steel which held the kiln together as it expanded and contracted and attest to the rigours of the firing process. Medalta’s beehive kilns historically fired a wide range of ceramic products and now serve as distinctive classroom and exhibit spaces.
Buffeted by a stiff breeze, we inspect the disassembly of the dome now underway. The partly open roof gapes like an eye beneath our feet, the exposed kiln interior an iris of pearl-like surfaces shimmering with glazes deposited in years past. Two years ago, the June 2013 flood inundated the area and washed out support from beneath the foundations of Kiln No. 2 and other structures. Subsidence of the kiln’s perimeter walls led to alarming deformation and cracking of the dome. Structural integrity of the masonry dome critically depends on compression within each concentric row of tightly fitted brick and, because of this, rebuilding the entire dome is the only means of repair.
After extensive documentation in measured drawings and rectified photographs, conservation began two weeks ago with the removal of the protective outer brick shell to expose the inner dome of fire brick. Disassembly of the inner dome will proceed row by row, a painstaking process that involves the removal of specially tapered “key” bricks that occur at regular intervals and effectively lock each row in place. Once removed, collapse of the ring is inevitable and the bricks must be removed quickly. Each row is numbered and salvaged bricks are stored on a separate pallet for reassembly.
Rebuilding of the dome in about a week’s time will use the salvaged fire bricks, traditional lime mortars, and generations-old techniques. Aiding the masons is a curved wood template and steel armature temporarily mounted onto the central stack. The template pivots around the stack and establishes the position of each row and, ultimately, the curvature of the reconstituted dome. Each row of fire brick is re-laid and tightly fitted with new keys in a reversal of the disassembly process. The finishing touch will be the application of a protective “mud cap” or layer of clay or lime mortar. Once complete, the repairs will give new life to this unique structure and maintain its historical integrity for the use and benefit of future generations.
Written By: Fraser Shaw, Heritage Conservation Adviser