Essex Rock & Minerals Society Field
Trip
Bulmer, Essex, 21 August 2004
Our first port of call was the Bulmer Brick and Tile Works (BB&T). It was bright sunny day as we donned wellingtons before being given a guided tour round the works by the senior member of this family business, Mr Peter Minter.
This brickworks may have the air of some pseudo Victorian craft centre for visitors, it is not, but it is most definitely a fully functioning traditional brickworks that, on the outside, hasn't visible changed much over the centuries. Peter was born into the business in the early thirties and as a small lad learnt the trade inside out from the old boys already working there. So the collective experience, that goes into today's brick production here, dates back to about 1870. Prior to the second world war they had three kilns working. At the onset of war all brickyards in the area were forced to close because they had open top kilns. Their glow could be seen from the skies and would have made an excellent navigation beacon for enemy aircraft. BB&T were forced to close two kilns for the same reason. They were able to continue with their third, as this was a downdraught kiln and closed to observation from above.
After the war the other small brick companies in the area were offered Government grants for new plant to start production again. Sadly, their business did not qualify as they had never stopped production! The other companies soon went out of business as the new technologies were not economically sustainable for the type of clay in the area. They were lean times for BB&T but they struggled on supported by their family farm (adjacent). Fortunes changed in 1974 with the upstart of preservation and conservation of old buildings. Peter's expertise gave them an edge on their competitors, and this brickyard now produces specialist bricks to the requirements of this sector of the building industry.
The starting place was the quarry, which boasts a small outcrop of London Clay.
In this view there are two heaps of clay, left weathering before being processed. The brown heap in the centre came from the level at which were standing. The darker heap to the left hand side and slightly to the rear is the "blue" London Clay. (Weathered surfaces of London Clay usually turn brown as they oxidize.)
From the London Clay heap, a shark's tooth or two were picked up by a couple of members.
This
view is a close-up of the top of the quarry face as seen on the right
of the picture above. (The overall colour has been altered slightly
to show the markings to best advantage, it was more red.)
The light horizontal bands, just below the top soil, are volcanic ash bands. We never did get close enough to scrape away the weathered surface to map and count them. (Well, I didn't.) However, Bill George had his notes from a previous visit some twenty odd years ago which stated that 4 bands were visible then!
These were said to be a continuation of those that outcrop at Wrabness where they occur above the Harwich Stone Band. (These same "Ash Bands" outcrop at the Naze, Walton and Harwich but I have never viewed them to-date! Also note there was no evidence in this quarry to suggest the presence of the HSB)
Peter
Minter is in the middle of our small group explaining the strategy behind
the excavations. Note the continuation of volcanic ash bands at the rim
of the quarry face.
The London Clay was about 2m below the base where we were standing. Nearby, a small pit descended to this level but water obscured the clay. It was said to be sort of laminated, or that's how it behaved when being dug.
From
where we were standing (above) this was the view looking towards the brickwork
sheds. Notice the various piles of clay weathering. The nearer the sheds
the more ready the clay is for processing. The piles are moved closer
as they become ready for production. It takes about 12 to 18 months from
digging the clay, to being used. The weathering is to allow salts in the
clay to be washed out naturally. (One often sees natural salts effloresce
as a white crust from brickwork, especially where subjected to occasional
damp. Some clays give more problems than others.)
The
clay in the foreground has been through one stage of milling and sieving
already. This is barrowed away for the final stage where the composition
is adjusted by adding sand to stabilize the shape of the brick during
firing. The mix is then run through a pugmill and tempered with water
to correct the stiffness to suit the moulding process.
The barrows are all made by the workers themselves. Basically the height of the handles matches the height of the user for comfort and better leverage when emptying.
In
one of the moulding areas we were able to watch work in progress. The
wood mould was first dusted with dry fine sand. The bench was lightly
dusted with sand and a clot of clay was roughly shaped on the bench and
then thrown into the mould (now placed on the tree stump).
The height of the stump and the bench are individual to each worker, so as to reduce fatigue.
The action of throwing the clot ensures that the mould is fully filled in one go.
The
excess clay is removed with a wire bow. A flat wood pallet is placed on
top and the mould inverted and then lifted off. The pallet with the newly
cast brick is placed on a hack barrow with others to be removed to a drying
shed in this instance.
The bricks we observed being made were specials for St Pancras and were removed to a drying shed where they were stacked individually on shelves. The temperature and humidity of the shed was controlled during the drying process. Once the bricks were dry enough they were turned over (because the base was still damp) and re-stacked in an open diagonal pattern on top of one another (skintled) to promote air flow until they were considered dry enough. This they tested by gentle knocking two bricks together and listening to the "ring" plus a sense of touch, all based on hard learnt experience.
For me the drying process was a revelation. We were told that the bricks shrink by about 12%. The moulds are made larger to compensate. Having had a little experience casting (metal) I was familiar with the problem and always associated it with the "firing" process. The surprise was how much the bricks shrink in the drying process. Quite logical when one thinks about it, but very dramatic when seen for real. It was one of those moments that graphically explain the problems of subsidence and heave of buildings due to clay subsoil.
We had a little detour to two small pits, long since filled with water. At the end of the larger of these (and a bit) there was a seam of clay suitable for tile making! It turns out that this was the mottled clay of the Reading Beds. (A formation that appears "below" the London Clay)
These
are the drying hacks used for their standard stock bricks. The height
of the hacks is about 4ft (1.2m) at the eaves. (The picture was taken
from low down.).
As the bricks come from the moulding shed they are stacked a single course at a time, when dry enough they can then support another course of new bricks from the moulding shed. I did see some metal sheets that they lay along side the hacks to lessen the effects of driving rain in bad weather (loo boards).
The production of the bricks in this photograph was conducted in another shed. They used aluminium moulds for these. It was said that they had tried everything to replace the wood ones which wear rapidly. Aluminium was the best metal found as it held the dusting coat of sand like the wood ones, with the added benefit of a longer working life.
The
mouth of the Kiln, it felt cool so I presumed it was being loaded, as
to being unloaded! (Even this barrow has a special name, "kiln
barrow" or sometimes "crowding barrow".)
The kiln is a circular structure and works on a downdraught principle. This type of kiln is quite often referred to as a "beehive" kiln. BB&T's is coal fired! Peter said that it could accommodate a maximum of 12,000 standard bricks.
Within the recent past the brick dome had to be rebuilt. It is just bricks and mortar and constructed without any support. Peter remembered that the first time it was rebuilt he was four years old and the old kiln master scratched pictures in the earth and told him how to rebuild it next time. When they first tried it kept collapsing, then Peter remembered that he was told you need four bricklayers to start and as it progresses you needed three, then two and then one. They had started with two and couldn't do it. Once he remembered you need four, work progressed successfully!
Whatever one thinks this is a traditional brickmaking business that specializes in making original bricks for specialist work. They also make tiles, terracotta mouldings and cut bricks (sculptured shapes) and lime mortar mixes to fill every need for heritage work, or if the requirement is there, new buildings.
It was three hours of pure bliss, listening about and observing the operation of these works. Martins flying in and out of the sheds, other wildlife whistling in the trees. Eco-friendly beyond belief.
After lunch we continued on to Hill Farm, near Gestingthorpe. On the old sunken lane and about 100m from the farmhouse, lays a series of "Sarsen Stones" on the bend.
Reasonably
worn sarsen stone but still showing the mammalated surface very well.
Another
sarsen but well worn. The size of this was very similar to the others
featured here, very roughly about 1.2 to 1.5m in length. The black dot
is the lens cap of my camera.
There were other smaller bits lying around but I didn't have that much time in the lane because of all the traffic caused by the hoards on this field trip. I had no wish to tempt them to run me over!
This
sarsen stone, perched upright in the bank, is also well worn and similar
in size to those above. Unusually, it has a series of random holes penetrating
it. They all looked natural.
From the positioning of these and other smaller ones in the lane, I suspect they were placed there by the farmer.
On their land is evidence of Roman buildings and over the years the site has been excavated by the Cooper family, from this they have developed a small museum of the artefacts and published a couple of books. Mr Cooper senior gave us a short talk explaining; the site, the finds, and time scale of Roman occupation. They also said there was some evidence to support an Iron Age settlement, and as there were some flint finds, including an arrow head, I would not be surprised had this site undergone human occupation from way back to the present. In one of the barns they have lain out all the odd artefacts that they have found. Also included are fossils, flints and erratics (rocks that are out of context, transported and left during the ice ages) from the boulder clay. Curiously, there were a few examples of what looked like iron slag (refractory product).
We
then marched off across the fields to the site of an almost circular depression,
some 2.5m deep and some 5 to 6m diameter (dimensions very approximate).
This hole appeared in the Spring of 2002.
We were asked "what we thought about it?"
Sink hole, swallow hole, were names that were spoken. There was almost universal agreement that this one was caused by the dissolution of the chalk not too far below.
From nearby bore hole data, the site of which was about 5m higher than ground surface here, chalk was encountered at 19.5m.
I
wandered off down slope, leaving the pundits gathered around the hole,
with the cheerful thought that one or two might fall in.
There was talk of underground rivers and cave complexes, chalk workings etc. In this instance I think these causes for the holes are about as unlikely as a UFO landing.
Although to be fair, behind from were this picture was taken, a small copse marks the site of an old clay pit, whilst over the road, further down slope towards Belchamp Brook, are couple of old small chalk pits (not viewed on this occasion).
The more experienced in geology of our group said that the topography and stratigraphy were just right for the development of these structures by the dissolution of the chalk by ground water. They talked of acidic water travelling through cracks and fissures in the chalk. I think I heard the term "solution hollow" applied. Perhaps the term "solution cavity" would be appropriate for the chalk below. So what does it look like below ground? If only they would let me loose with a JCB digger for a day or two!
Try this link for a resistivity survey of another location, it shows the cracks in chalk amazingly well plus some rather strange curved and circular structures that are said to be completely natural. I bet that choked a few archaeologists?
And if you wish to see a sketch of how a beehive kiln works, try this link.
N.B. The notes above are just my recollections, views and opinions. Whether right or wrong they do not represent anyone else's. I enjoyed the day out!
Roger Coleman
All photographs & text © Roger Coleman 2004