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How Margory Was Repaired - September 2010

How Margory Was Repaired - September 2010

During the winter of 2009/2010, I spotted that Margory was needing repair. A temporary bodge got me through the necessary Spring firings to produce pots for the 2010 Summer season, however, a more permanent repair had to be undertaken before Marg could be fired safely again.

I decided that the repair had to be completed before the pot-making season of Autumn/Winter 2010/11 began. I didn't want the flow of making pots to be interrupted by kiln-repair activities, and I thought it best to get the job done before the wet and wild weather arrived.

This section gives a step-by-step explanation of how that repair was made.....

The first step was to take the outer insulating layer off the whole length of Margory, so that I could take a good look at the brickwork.

Although I could see from the inside of the kiln that bricks were moving, this gave me the first opportunity to see the problem from the outside...


Looking down the spine of the kiln, you can see that the line of bricks just left of the key-stone were dropping.

Margory is made with no mortar between her bricks, relying on gravity and a good shape to keep her standing, When firing, particularly when reaching the hotter temperatures with the chimney closed down, pressure builds up inside. This pressure lifts the archway. Normally, the keystone would drop a little during this ''lift', which strengthens the structure, but the length of Margory's keystone had stopped this from happening. Instead, the bricks to one side of the keystone were dropping to compensate. This does not strenghthen the structure....!

I decided to build a shape which would support the arch of the kiln, whilst I removed one brick at a time, and replaced it with specialist 'concrete'. I would replace all the bricks that had moved.....

I decided the supporting shape need only prop up the top curve around the area undergoing repair. The theory being, as I was only removing one brick at a time, the rest of Margory's archway should stand strong..

To make the supporting shape, I took two measurements..... the width of the top section of Margory's arch........

.... and the greatest height in the middle of the curve....

These measurements were then drawn onto a piece of 0.5" thick chipboard.....

Using them as a guide for width and depth, a chain was hung to form a curve. I then drew round the curve....

The resultant curve was then cut out of the chipboard, twice....

The two curves were joined with 18" lengths of wood....

.... and the whole shape covered with hardboard to make a rigid shape.

A 'letterbox' was cut in the shape. Once the shape is placed inside the kiln, this will be lined up with the brick that is to be removed.

The wooden shape was placed inside the kiln, and held hard against the top curve of the kiln with extendable props. It was positioned so that the brick to be removed could be seen through the 'letterbox'.

Much as it pained me, for I know the cost of a single kiln brick, I decided, rather than knock the brick through the 'letterbox' and try a retrieve a whole brick, to cut the brick in half and let it fall in, in bits. This seemed a more cautious approach. I drilled into the brick.....

....creating a cut across the centre of the brick.

Once the brick was completely cut in half, it was easily pushed down through the letterbox in the former, into the kiln,

The mortar below the removed brick was then carefully removed.

Crawling into the kiln, I placed a piece of wood up against the letterbox, and, trying very hard not to knock the supporting props of the former, held the wood in place with further props.

This gave the hole where the brick had been removed a base. I also lined the brick space with thin cardboard. This is so that when I poured the refractory castable into the hole, it would not bind to the brickwork alongside.

I mixed sufficient refractory castable (a cement capable of withstanding kiln temperatures) to fill the brick gap. Being cast in the brick space, once hardened it is an exact fit.



This process will be repeated, replacing one brick a day, until all the falling bricks along the length of Margory have been replaced. I think it may be possible to remove a single brick without even the use of a former inside the kiln: it seems unlikely that losing one brick would cause the kiln to lose its shape, but I don't want to take any chances!