Extract from:
A study of limestone quarrying at Llanymynech
Written in 1984 by Harvey Kynaston

THE HOFFMAN KILN
STRUCTURE, LOCATION AND FUNCTION

STRUCTURE OF THE KILN

At the turn of the century there was a demand for finer lime than the familiar inverted bottle shaped kilns could produce. It was decided to build a superior type of kiln at Llanymynech which could provide lime by firing with less coal therefore producing a finer lime for industry. The Hoffman kiln today is very much overgrown. Plants such as ferns, mosses, nettle and ivy have taken a firm hold on it and there are even a number of sizeable lime trees on and around the site.

Despite this ever encroaching vegetation, the condition of the kiln is remarkably good. Its oval shape with steep sloping sides has a circumference of approximately 110 metres and each long side has a length of 40 metres. At one time the entire kiln was covered by a curved galvanised roof but this has long since disappeared, leaving a total height from the present day floor of about 4 metres or 40 layers of bricks. While counting these layers it was interesting to note that each layer alternates, having bricks lying end on then side on and so on.

At one end of the kiln (nearest the canal) stands a tall square section chimney approximately 30 metres high which took the smoke away from the area and probably served the purpose of "drawing" the draught through. Over the years its double skin of bricks has weakened and now it is supported by an iron brace.

Along each side of the kiln are 6 arches 1.25 metres wide and 2.20 metres high and they provide entrance to the formidable interior in which stands a long central pillar to support the roof. In the roof can be seen small square holes spaced out at regular intervals. The function of these will be discussed later.

To the left hand side of each arch is a draught hole 90 centimetres wide and 80 centimetres high leading into the kiln and also beneath its floor.

Approaching the site from the A483 one can still catch glimpses of the sleepers and rails of the tramways which served the kiln with trucks carrying limestone or coal.

It has already been mentioned that this structure was intended to produce a finer lime at the turn of this century. It is one of only a few in the country, if not Europe, and by looking at the 1.70 metre thickness of its walls, it was surely built to last. And yet the Hoffman kiln closed down in 1914 and was therefore only in production for about 20 years. Why this was so is one of many unanswered questions. Perhaps one or all of the following possible reasons led to its closure:

Complaints of smoke
Better quality limestone at Porthywaen
Outbreak of first world war
Poor maintenance and deterioration of the canal
The Hoffman kiln never performed well

INSIDE THE HOFFMAN KILN

SKETCH MAP SHOWING LOCATION OF HOFFMAN KILN

FUNCTIONING OF THE KILN

There are several speculations as to how the kiln actually worked. It is certainly different from the “inverted bottle” type kiln in that limestone is loaded through its arches and not from above.

Coal (presumably a slow burning anthracite) arrived by horse drawn barge on the nearby Montgomery canal, now a branch of the Shropshire Union canal, and was poured into the kiln through holes in its roof by the firers.

There are several holes to each section of the kiln but before coal was poured into them iron rods were held in position through the holes so that the packers beneath could skilfully build a stack of limestone rocks around them. Occasionally, a rough built stack would collapse and the entire structure would have to be built again. The limestone loaded trucks which descend on an incline from the rock face, arrived in pairs and were probably pushed around the kiln until they arrived at the correct arch. There they would be swivelled through 90°, run on temporary rails into the kiln and unloaded. From the scanty evidence of existing trucks it is difficult to say exactly how they were unloaded. The type of truck can be found under the rock face and also the type of tipping mechanism employed. However these trucks were relatively small and it could be that a larger rectangular truck which had one side left open was used for travelling up and down the incline.

It is known that each section through its respective arch was packed and fired in succession rather than every section packed and the whole kiln fired. In this way there was a sort of rotation - as one kiln was smouldering, another was being packed and another was being raked out. Their timing was such that by the time the workers had completed one “lap” the first section would be ready to rake out. One wonders how long the whole process took, - twelve hours, a day, three days? Again many questions still remain unanswered.

Surveying the now overgrown kiln shrouded in its green canopy it is difficult to get an impression of the working conditions that the men must have endured. The first factor that springs to mind when considering a modern busy industrial concern is noise. But would it have been noisy working at this kiln or indeed any other? What sounds would one hear? A steam engine from the adjacent kiln, the rumble of trucks descending the incline, the occasional steam train, the odd blast from Llanymynech rock but certainly little mechanical noise.

There must have been more uncomfortable aggravations than noise. Dust for instance, heat certainly, and although the tall adjoining chimney must have carried much of the smoke away, there was probably a constant stench of burning to anyone in the vicinity.

It is hard to believe, walking round the kiln, that men actually worked here. Conversely, I am sure it would have been difficult to convince a worker in the heyday of the kiln that in seventy years time, cows would be meandering in and out of it and trees would be growing on top.

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The following diagram and text are from an unidentified document. The description relates to the use of the Hoffman kiln for brick making but the principle of a ‘continuous rotary burn’ applies to the lime kiln.

Hoffman kiln

This is a continuous kiln, that is, the fire never goes out as it is transferred from one chamber to another. To facilitate loading and unloading, the kiln is divided into a number of separate chambers, usually 16, having 8 on each side with dampers between them which may be opened for the fire to pass from one chamber to the next. All the chambers in one kiln are connected to a single chimney shaft. As the fire passes round the kiln so the chambers in front of the actual firing zone are gradually warmed, and the chambers behind cool off slowly. Although the burning time is only about 3 days, the bricks are in the kiln for about 10 days to allow for raising the temperature and, after burning, subsequent lowering of the temperature before unloading the chambers