The end of cobbing party - or is it the end .... ?

Saturday 7 June - After working in the Sedgwick Museum during the morning I had a wander around Strawberry Fair, which was looking sparsely populated due to dire forecasts of rain. Then I made my way over to Northwest Cambridge to see how the cobbing had progressed and meet up with other cobbers for an "end of cobbing" party.

Walking onto the site for the first time in weeks I could see Kirsten at work with Karen and some cobbers from previous weeks, folding up tarpaulins and tidying up the site for the party. A huge amount of cobbing has been done. The rounded space-age torus of the primary school had been built, so had the community centre, there were many more houses and flats and the ground plans for many more buildings had been laid out.

We drank cava among the new cob buildings, sitting on the roof of the primary school (very naughty!) and Kirsten made a small ball of champagne cob to fix a small hole in the primary school roof. Karen and Nina thanked everyone for their work, Cindy and Al for the wonderful food, and Kirsten for her relelntless efforts. Kirsten herself was adorned with her order of the Marigold regal gloves and sceptre. The sun shone upon the new cob landscape, defining sharp-edged cob shadows across the gravel plain, and we all toasted the success of the project.

Later in the barn we ate a selection of delicious cakes with a cup of tea and it was explained that the cobbing might possibly continue to complete the models of the research buildings. It's not clear yet exactly how this would be funded or carried out, but the possibility seems to be there - hurrah!

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Gravel Hill particle size analysis

Gravel Hill subsoil particle size analysis

A preliminary analysis of the particle sizes at the Gravel Hill site shows why it is a good site for cobbing - both now and in the Iron Age. The glaciofluvial debris (probably from MIS 13, just over 400 kyr ago) includes a good mixture of coarse clasts, sand and fine clays.

Of the material finer than 70 microns (.07 of a mm), a relatively high proportion is very fine, including the clays <2 micons, .002 of a mm.

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Cobbing day five: the last day (for our group)

Cobbing in Northwest Cambridge day five

The wind was chasing straw in little tornadoes around the site as we rolled the wheelbarrows onto the gravel plateau we have been working on. John was in the digger and I signalled that I could drive the tipper truck down onto the site; he gave a "thumbs up" and I sat myself down in the tipper truck, strapped myself in and waited for John to finish shaping the load of cob into the tipper's bucket, then drove it down and dropped it off next to the row of houses we had been shaping.

I handed the tipper over to Reece who was gaining some tipper driving practice. Later he went on to try out the digger, which he really enjoyed. "It's really easy once you get the hang of it!". I had brought some foam for people to use as kneelers but the wind was blowing the foam all over the site, so I threaded some wire through it to give it some extra weight. Even this wasn't enough but it certainly helped. The gusts of wind were blowing my jacket and small herds of rolling gloves across the site. We used stones and breeze blocks to weight them down.

I turned to the corner of the block of flats I had worked on yesterday. It looked wide in relation to the measuring point - an iron fence post  stuck upright into the cob where the building turned a corner into an "L" shape. I took out clumps of straw handful by handful and tried to reduce it to a manageable size, piling the cob around and on top of it. Kirsten said later: "That's bad cobbing. You should work round things in layers like a coil pot; otherwise it could slump or even collapse." I realised it wasn't going well, so I filled a wheelbarrow with cob and went over to the terrace of houses we had been building throughout the week.

Shaun was working on the house he had been carefully developing all week, making meticulously vertical layers famous for their smoothing. Li was working at the far end, as was Mary, each on a separate house. I looked at the set of three houses right at the far end of the row and decided to see what I could do with them. The walls had almost reached the 55 cm height needed to complete the  vertical walls and start working on the pitch of the roof. I poured some water on the top of the block shaped houses, put some cob in a layer a few centimeters thick on the top, and stuck some bricks in the cob to bulk out the shape without interfering with the pitch of the roof. Then I piled on cob; when each one seemed to have all the cob it could deal with without slumping I switched to another house. By the time I came back to the first house, it would have dried enough to add some more cob.

 Natalie told us about the lecture she had been to yesterday evening. "The speaker was saying that science was essentially completed, and all that remains is to tidy up after the party. I think he was partly being provocative". We agreed that in view of the history of science it seemed rather unlikely that the task of science was really so close to completion. There may be intervals when scientific understanding appears to be changing only gradually, but then something like a paradigm shift occurs and lots of new insights are gained relatively quickly. The difficult thing is to anticipate when such changes are likely to occur, and sometimes to recognise the shifts when they do occur.

The weather was improving to the extent that I wished I had put on some suncream. When the wind blew it was chilly; when the sun shone it was rather too warm to wear a coat. The cob houses were making progress but the upper walls were tending to sag out before they dried. I reckoned that some of this was inevitable and could be dealt with later, so I carried on cobbing. Karen, who had been trying to work out a measurement problem with another little group of houses, came over. "The problem was with the formers" she said. "When I checked the measurements, the outside of the frame was the measurement that the inside should have been. So all the bases for the houses were too small. But at least I know what went wrong - I'm glad I checked the frames". She strung a piece of twine between posts across the ridges of all the houses. "We'll make the roof ridges come up to the same height rather than make the houses exactly the same size" she decided. Mary had already noticed that some roof ridges were higher above the ground than others and this explained it - the ground falls away slightly towards the end of the terrace, so the houses had to be slightly taller to come up to the same height.

Li was very pleased with the way her house was progressing. "This is absolutely perfect, I'm very happy!" she declared, laughing. Shaun told us he had just sold his collection of over a hundred DVDs on Ebay, only keeping a few selected ones, such as the Lord of the Rings trilogy and Battlestar Galactica. He said that Ebay had a price cap on postage which means that, if you're not careful, you can end up paying more for postage than you can charge the purchaser. Karen suggested that Shaun could build the walls up faster, but he was reluctant: "I'd rather wait till they dry. If you put too much on the walls will bulge out". Karen offered to do some but Shaun said he would rather do it all himself: "This one's my baby!"

Lunchtime had arrived and we went over to the portacabin where Kirsten and Al had been preparing a treat: home made pizzas cooked in a cob oven. Al had prepared the pizza bases and rolled them out thin on flour; we put on a thin layer of spicy tomato paste and some pepperoni and mozzarella cheese. Outside Kirsten was feeding the pizzas one at a time into the cob oven she had made. SOme weeks before,  a "box" of cob had been filled with sand, some firebricks laid, then a mound of wet sand used to shape the interior of the oven. Little brickettes of wet cob without straw had been laid all over the outside of the mound, as if constructing an igloo. Then several cm of cob with straw were put on the outside and pressed in, to squash the brickettes against the sand. Then the entrance could be cut: 63% of the height of the interior of the oven, and the sand could be hollowed out. After a week's drying it could be test fired, and then cooked upon, using a baking tray with a handle fitted to slide into the oven.

The pizzas were absolutely delicious. Li was ecstatic. "This is the best pizza I have ever eaten in my entire life, ever! This is the best  food ever!" She said. She wants to build a cob oven and Shaun said he would like to do the same. The pizzas were smokey and crisp, full of flavour and with a pasta salad and couscous to go with them, we had a truly excellent meal.

I tried to get a photograph of everyone but the results were somewhat mixed (see below); the wind blew the camera over at one point in spite of it being on a level base with one stone in front and another behind it.

I had found a small mold of an ammonite on the second day and used the Natural History Museum's "British Mesozoic Fossils" to identify it as Portlandian. It fairly closely resembles Titanites, though it looked rather small to be dignified with an identification as Titanites giganteus - it's about 8cm in diameter.  It is very similar indeed to the Portlandian genus Blanfordiceras, which is probably what it is, which suggests that it is from the Tithonian time period, 145-150 million years old. I had supplied the eroded part of the centre of the mold with a mold taken from a related ammonite. Kirsten had sieved some subsoil to try using it for casting, but the grain size was still too large to get a very detailed cast from it. Luckily there was a small patch of the pale yellow Cambridge clay of the sort used for making Cambridge white bricks near the portacabin, and I hydrated some of that to make a good casting mix and got a good, detailed cast from the mold.

Back to cobbing, and trying to get the roof ridges straight and at the right height on the little houses. This takes a lot of work with the spirit level, especially the one with a 45 degree bubble. I worked at it till I reckoned there was little more that I could do in terms of precision today. Kirsten said she could "sharpen" the houses tomorrow - there will be an open day at the site between 11am and 4pm on Saturday 10 May, everyone welcome!

I turned back to one of the big model blocks of flats. Reece has put a line of cob along the base of the straw bales making up the high part of the block, and I went over it with another line of cob - doing the cobbing the proper way this time! The wall below still slumped a bit under the extra weight, but |I reckoned this was probably acceptable. I noticed that if I tried to "pat" the wall back into shape with the plasterer's trowel, it tended to "rebound" off the semi-elastic straw behind, creating a cavity between the straw and the cob that was a potential weakness, so I tried to avoid doing that.

Shaun reveals the true scale of our building work, while hopping down off the roof.

The cob piles on the tarpaulin had begun to dry amazingly quickly over lunchtime - the sun was shining and there was still a breeze so it was ideal weather for drying, but of course we needed our cob wet so we began to cover it up between shovelling it into wheelbarrows. The last task of the day was to fill in the base of the big building with the breeze block formers creating a long thin cavity, so we took barrowload after barrowload of cob over to it and filled in between the walls Natalie had constructed. When the barrows were half empty we could lift them up and tip the contents wholesale into the centre of the building, then smooth the heap out to make a reasonably level covering. Then it was time to pack up and finish the day's cobbing.

At the end of the day we thanked Kirsten, Karen and Natalie and gave them a bottle of fairtrade wine as a thankyou, and Kirsten was given a bejewelled plastic "Cob Ruler", that she used to bestow knighthoods of the Order of the Cob upon the volunteers. Li was particularly delighted and beamed. "I'm so happy!" We hope to see each other again on some of the open days at the site, especially on 31 May at the end of the full project. All the best to the cobbers who went before us, and those that will come after, and thanks to the artists and organisers of this excellent project!

Karen receives "The  order of the Cob" from Kirsten

Natalie leaps up to repair a dent in the wall she has just spotted.

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Cobbing day four

Cobbing in Northwest Cambridge day four

Today, Thursday, was wet from the start: drizzle was falling as I cycled up the Madingley Road to get onto the cobbing site by cycling past the Institute of Astronomy - this is a slightly shorter route from my house. A new Karen, Karen Guthrie, was there in the barn - not the same as the first Karen, Karen Wydler, who was there on day one.  Karen Guthrie is one of the artists directing the project along with Kirsten. Since she was on a visit to Highpoint Prison to discuss an art project involving the prisoners, Kirsten was not here today, so  Natalie and Karen were in charge.

After a cup of coffee we tramped up over the hill towards the site. John wanted the tipper truck driven with some cob onto the site and Mary did the driving, after putting a handful of dry straw onto the seat of the tipper in order to stay dry. Li was worried about the rain. "It will all collapse, it will all fall down" she said. "We should work longer tomorrow instead". She waited till the rain stopped (temporarily) before joining us on the build. We looked at the little row of houses. I could see something this morning that I had somehow missed yesterday: the ridge of the roof that I had put onto the house wasn't straight - it was dropping towards the back of the house. I put some more cob on the roof and aligned it using a spirit level, and added a bit more "wall" to another house, bringing up the wall level to the point where the pitch of the roof could begin.

Natalie was working on the block of flats for which we had created a platform on Wednesday. She arranged straw bales along the far side of the platform where the flats would be multi-storey. We spent the rest of the morning mixing up cob to a sloppy slurry to get a smooth finish on the existing platform and packing cob around the base of the straw bales and in between the bales to stabilise them. It is important with cob not to try to build too high in one go, particularly if you are building vertical surfaces - otherwise the semi fluid mass will slump and collapse. This becomes particularly likely when the cob is wet, and it was collecting water from the rain, both sitting on the tarpaulin and once built into the models. Levelling the platform was very similar to working with wet concrete and we drew a timber across the surface repeatedly, with a sawing motion, to fill in any cavities and leave a smooth finish.

Karen set us the challenge of finishing the terrace of houses before the end of Friday so more cob was put onto these. The house that Shaun had been meticulously building received a generous dollop of extra cob from an unknown hand. This added height to the structure but also made it bulge out at the  top, rather like a mushroom. Shaun looked at it with a pained expression. "I'm going to sort that out before the end of the day".

It was lunchtime, and we were told that it was a hot meal, but John was keen to empty a load of cob from the skip so I stayed out to take two loads of cob down to the working area in the tipper. The cob slumped nicely out of the bucket and as I drove it back towards the skip I saw Al walking up the hill. "Your baked potatoes are getting cold!" he called. But John had one more task in mind - using the tipper to to load some more water into the skip for another cob mix. This was soon done - I had to be careful to drive the tipper slowly so as not to let waves build up and slop out the water on the way to the skip.

John loads the tipper with a fresh consignment of cob

The baked potatoes - in the end I ate two, because there were some spare - went down a treat, with beans, cheese and vegetables on the side and a hot cup of tea. We were all pretty soaked. Biky Wan came along from the  Northwest Cambridge development project and explained what was intended for the project, in particular in phase one, and some of the details and scale of the buildings involved. Phase one will include accomodation for 300 students and a primary school and multi-functional community facility will be built so that meetings and concerts can be held on the site. There will also be accomodation for visiting academics, which will help Cambridge University keep up with other top universities around the world in terms of providing accomodation for visitors, something it currently struggles to do because of the lack of housing space in Cambridge.

John's doberman, Ralph, gets a bit of attention in the barn

I always find Madingley Road a bit of an obstacle and a hazard when trying to get from the West Cambridge site over to the Bullard labs, so given that the two sites will be quite closely integrated, I asked if there were plans for a bridge or an underpass to connect the two. Biky said no, but she would pass the suggestion along. Shaun asked about the self-build area that is part of the planned use of the site and Biky said that it would benefit from the ecological aspects of the planned development, such as non-potable water recycling, to give a good potential for ecologically small footprint constructions.

Karen was getting concerned about the time so we thanked Biky and prepared to get back on the site. I brought the tipper truck down to collect the breeze blocks - about 30 of them - that were delivered yesterday. I couldn't get right up to the barn because a gate was locked so I had to carry them all over to the tipper and heave them into the bucket before taking them over to the site. The plan is to use them as formers to create a narrow gap that is part of the building design - a 1.2m wide gulley running down the length of some of the blocks of flats. Together with Natalie I wrapped the blocks in cling-film to make them easier to release from the cob and set them in a vertical row like black teeth along the line of the gap. As a final flourish Natalie wrapped the entire row in a final band of cling film.



Li had found the rain a bit much and went home and Mary - who seemed pretty surprised that we were working at all in the rain, but valiantly worked on herself anyway - was only there for the morning so we were a bit depleted in numbers, but Natalie, Shaun, Reece, Karen and myself worked on as the drizzle drizzled on, finishing up by putting some more cob on top of one of the big models of flats. There were divergent plans indicating the height of this building, so we can't complete it till we know for sure how high it will finally be.

Karen after the day's cobbing

When we finally packed up and got back to the barn there were some warm chocolate brownies waiting for us. These looked curiously similar to the model buildings we had been working on all day, although on a smaller scale. Shaun - who had inadvertantly sampled some of the cob mix earlier in the day - confirmed that the brownies tasted far, far better than the cob. We all ate all the brownies we could, and there were still plenty left over. Thanks Cindy!

Cobbing day three

Cobbing in Northwest Cambridge - day three

Kirsten had been asked to "tidy up" the straw bales being used as a source of straw for the cobbing. There are around 100 of them so tidying them up was no small feat. We brought stout gloves this morning in order to stop the bailer twine cutting into our fingers as we shifted them; Shaun had thoughtfully brought three pairs of gloves so everyone was equipped. John ("Jez") the digger driver showed us how to bounce bales from the stack using a strategically placed extra bale as a sort of stepping stone or trampoline - you throw the bale you want to move onto the spare bale, it bounces off and travels much further than it otherwise would - hopefully in the direction that you intended.

In this way we constructed a tribute to Carl André who made the famous "Equivalent VIII" sculpture exhibited in the Tate Gallery, using the same ratio of 6 to 10 for the arrangement of blocks. This was not at all pretentious (hem hem)  and actually looked quite neat, thus satisfying the twin demands of aesthetics  and other people's need for tidy arrangements of things. Then we could roll up our sleeves and get back to cobbing.

I had reached a point in one of the houses I had worked on where I could begin to construct the pitch of the roof. Glen had discovered that the roofs could be constructed in one fell swoop, allowing their inclined surfaces to be worked upon in a single mass. Shaun pointed out - very helpfully - that one of the spirit levels had a 45 degree bubble in it, so before long I was using that level to correct the angles and produce a magnificent and only slightly wonky roof.

I started adding bulk to the walls of another unfinished house when Kirsten summoned us over to a marked out area near the large model of a block of flats which had been laid out yesterday. "We need to construct level walls around this" she explained, "so that we can pour wet cob into the middle and make a nice level surface". With Li and a new volunteer called Sam I began working my way around the edge of the building, constantly using a spirit level to check that the top surface of the wall wasn't getting out of true with respect to the level points that Kirsten had already constructed.

This process had just got underway when it began to rain a little, and anyway it was lunchtime. We headed back to the barn to discover that Cindy and Al had concocted another very tasty lunch with toasted halloumi and olives and salad. Over lunch Kirsten explained that the previous group had presented her with a set of "ceremonial cobbing gloves" of the Order of the Marigold.

We were joined by Michael from the Cambridge Archaeological Unit, which is part of Cambridge University's Department of Archaeology. This is a commercial organisation but not privatised, and with strong links with the academics of the Archaeology Department, and has an excellent publication record. Archaeological investigation is required for any new development and while this can be simply surveys and remote sensing, if something is discovered, then the developer must pay for whatever archaeological work needs to be done. On average, Michael explained, an archaeological site is discovered at a rate of about one per kilometer for a project such as a motorway, and archaeological costs can be 3-10% of development costs. However, archaeological discoveries could bring major economic benefits from tourism as well as helping to understand the historical development of a region.

After lunch Michael went to explain some digger work that he wanted done to John, and we met up with him again on the archaeological part of the site, where about ten people were working on the archaeology. He sent us up onto the top of a pile of earth with some boards positioned as a viewing platform while he ran a circle around a dark circular mark on the pitted surface below us. Then he sprinted up the little hill to explain what he had just shown us. "That's the outline of an iron age round house. You can see another one over there and there are smaller ones as well. Those two lines cutting through the second round house are Roman field boundaries. This site was occupied from about 400 BC, up until the Romans invaded in 43 AD. The Romans reorganised the land usage and this site is giving us information about how those changes were implemented. In another part of the site we discovered indications of a Roman field irrigation system, perhaps for asparagus or vinyards".

The iron age people had kept cattle, horses, pigs and goats, and the remains of a dog had also been discovered. We went down to look at one of the round house excavations and Michael explained that the circular mark - about ten meters in diameter - was the drainage ditch maintained under the eaves of the thatched roundhouse to take away the water draining from the roof. In the roundhouse itself people had lived together with their livestock and there were traces of hearths. The roundhouse would have been rebuilt every 10-25 years.

The whole site was marked by pits and trenches thought to be linked to drainage and the storage of crops. Michael speculated that wealthier individuals had a higher proportion of wheat rather than oats in their diet, and the people living on this site were not particularly wealthy. An unusual find had been part of a skull in a pond, perhaps put there for symbolic or ceremonial reasons. Michael stressed the huge difference in outlook between iron age cultures and most contemporary cultures.

Kirsten strode over the site towards us looking stern or perhaps anxious. "I'm not trying to hurry you but it would be good to get some more cobbing done!" Michael grinned and said he would keep the next bit quick, and showed us some iron age, Roman and possibly Saxon pottery in fragments on the surface. They could be identified to build a chronology for the use of the site. Some of the site remained to be excavated and it is very reassuring to know that the information about the past use of this place will not be lost forever. Thanks, Michael, for a great tour!

Back to cobbing and we finished levelling the wall around the model of the block of flats. With Sam I drew a sturdy timber across the surface, filling any holes with cob and levelling it. It is still a rough surface on top, but Shaun will finish the platform tomorrow, using the cob-smoothing skills he has developed working on the houses. Meanwhile Mary has been learning to drive the tipper truck.

We went back to the barn for some excellent drizzle cake and met David, an artist in residence on the site and discussed the span of history covered by this spot, and ate some very tasty lemon drizzle sponge cake prepared by Cindy. Right at the end of the day a Ridgeons low-loader drew up and delivered a pallet load of breeze blocks - to be used as formers to construct the narrow gaps between buildings. But that will be a task for another day!

A piece of Roman pottery from the archaeological site.

Cobbing day two

Cobbing in Northwest Cambridge - day two

Kirsten and Natalie looked thrilled as a white van pulled into the car park opposite the barn. "Digger John! Digger John!" Natalie shouted.  From the van a black labrador - Pyro - and an elegant doberman - Ralph - hurled themselves out and immediately made their way over to where they knew there might be food at the back of the barn, making a thorough inspection of the area. But there was only our early morning cups of coffee. Glen was not able to be with us today but his wife Mary was, for the morning at least. We were also joined by Reece, who looked slightly dubious about the whole thing, but this could easily be attributed to nerves. Shaun was also there and we were all ready to get cobbing again.

John gave us a stern introduction to the dangers of the mechanical digger. "It can chop your legs off easily" he pointed out cheerfully. He told us to grip a handle on the side of the cab if we were talking to him as he operated it, and to watch out for the bucket and arm swinging violently sideways. "I might use some non-PC language to tell you what to do", he said "but it's just to make it more memorable".

"Who would

like to drive the dumper truck?" asked John, who looks and sounds really quite a lot like Martin Freeman. No one else seemed to be jumping at the chance - Rees being young had never learned to drive - so I volunteered myself. "That's the stick that turns up the volume" said John, pointing to a sort of joystick on the side of the steering column. "Er ... what do you mean?" I asked, dimly. "It makes it go faster". "What about all these buttons?" "There's a horn that goes beep, and the others operate the bucket". It really did seem straightforward, so having strapped myself in I headed gingerly up the hill. At one point the motor slowed, so guessing that it was in too high a gear, I slowed down and this succeeded in getting it over the brow of the hill. So far so good!

Kirsten explained that she wanted us to trim the building models we had constructed the day before. Wet cob is a somewhat fluid material and it is quite capable of bulging and slumpring overnight as it dries. I shaved and cut away at some of the walls I had made yesterday, trying to bring them into line, and used a spirit level to check. This made it clear that there was a more serious problem with two other model buildings: the walls were tapering in towards the top. I poured water on to soak the existing cob and then applied coatings on the outside to make the walls more vertical. I'll find out tomorrow if these wall additions have stayed in place as they dried. I managed to add another layer to a house as well. Rees, learning about cobbing for the first time, was carefully adding a layer to one of the other houses, meticulously making the walls absolutely straight. "Another perfectionist" said Kirsten in triumph. I somehow suspect that I was not considered the other perfectionist.

But in any case other, larger plans, were afoot. Kirsten was planning to set out the floor plan of a block of flats. We used formers consisting of planks with small horizontal attachments which could be stood on, to hold the main part of the former vertical. The vertical section had to be placed on top of the strings oulining the floor plan of what will be a large block of flats in the Northwest Cambridge development. Kirsten had laid out mounds of cob  around in the interior of the floor plan and we scooped and pressed this towards the formers to make vertical walls precisely following the outline. Next we forked a much larger amount of cob into the interior of the floor plan. After lunch we were going to trample this to make the base of the new large building. "I want to set out the floor plans for all the buildings on the site, even if  we can't complete all the models", said Kirsten, recognising the daunting scale of the task ahead of  her over the next five weeks.

Lunch was an excellent spicy vegetable soup, again prepared by Cindy and Al. Ralph and Pyro, the two dogs, joined us for the meal and were rewarded with a few tasty scaps. Li was quiet today, perhaps exhausted by her relentless work yesterday, but still asking questions and making observations about the legal technicalities of building. "You can't build secretly, no", she said, "nothing must be hidden".

A huge, twenty ton orange digger had pulled onto the site during the morning and had been busy reshaping the topsoil ridge or "bund" that ran along one side of the site. The driver, Ricky, stocky and jolly, joined us for lunch and told us about the fifteen  ponies and horses he had kept at one time. One of them, which he said had "an upper lip like a camel", had repeatedly freed himself from a farriers "twitch" - a loop around the horses mouth used to control a horse while it was being shod - just by twisting its lips and was able to untie knots with them. It had also walked upstairs in his house one day!

I was expecting to trample the foundations of the block of flats in the afternoon but instead John took me over to the digger and told me to wait while he cleared the topsoil around an interesting pit that had been dug, originally with the plan of using it to mix cob. He  made it safer by reducing its steepness. I took some photographs of the stratigraphy inside the pit, which showed variations in the current speed of the water laying down the sands and gravel - presumably glacial washout sediments.

I was given careful instruction in the use of the digger - in particular not to grip the control levers, and to brace hands while operating the caterpillar tracks. The number of different movements - activated by moving the levers forward, backwards or sideways - seemed bewildering at first but before long I was mixing cob in the skip that was being used as a large mixing bowl for cob, and which was clearly more effective than the pit ever could have been - for one thing, any water put into the pit would have quickly drained out through the gravels at its base.

I learned how to load the dump truck with the digger and took loads down to where the cobbers were working on the block of flats.  In this way I escaped some of the hard physical work being done in the afternoon - Lee was so exhaused she sank to her knees at one point - but the concentration required to operate the digger made up for this evasion. At the end of the cob mixing by digger I was so phased out I couldn't remember anyone's name for about ten minutes.

After the end of the day's work we cut some plastic sheeting to cover the remaining cob mix made that day, and as we left the site I spotted a medium sized ammonite mould among the pebbles. The ammonite pebble must have split open late in the transporation process because the outside surfaces were fiercely eroded and rounded, while the ammonite mould retained a lot of detail - it should be possible to pin down the species. We have been told to "tidy up" the straw bales on the site so we have decided to make an impression of the famous Tate "pile of bricks" installation, but in straw.  We admired Ricky's work on the great earthwork bund at the side of the site, now shaped into a gently curving viewing platform. That was itself a remarkable and artful creation.

Cobbing in Northwest Cambridge - Day One

Monday 5 May 2014 - first day of the cobbing course. I cycled up  Huntingdon Road and turned left at a "Cambridge Research Laboratories" sign, down a dusty road towards the big 100 hectare site that is the NW Cambridge development. There, in a barn-like shelter next to a studio, was a small group of people drinking coffee around some straw bales. Kirsten Lavers is organising the day's activities, assisted by Natalie and a "guest artist", Karen.

Also there is Shaun, tall and enthusiastic, and Li, who calls herself  "Miss Li" initially, also enthusiastic but not nearly as tall. She is wearing a blue raincoat which stays on all day although the weather is quite warm and sunny. Four more people are expected but phone in to say they will be late. The introduction to the ancient art of cobbing begins as we sit in a semicircle on the straw bales.

Kirsten points out that cob-built houses are an ongoing process of building and repairing that keep people in touch with the Earth and with each other. They can provide good insulation and "breathe" well, allowing air to circulate. Li tells us that she was born in a mud hut in China and spent her first years there, and thinks their shape is much better than buildings with corners - good energy, good Feng Shui.  Li thinks houses in Cambridge are much too expensive and would clearly like to build a traditional house herself. But the object this week is not to create a dwelling but a large artwork - a scale model of the university's Northwest Cambridge development.

A typical composition of cob is four parts "subsoil" - sand, gravel and clay without much organic matter - one part sand, and a few large handfulls of straw. Cow dung provides an even better texture, but we will not be using that today. Even the builder's own urine can be used - but this, Kirsten hastens to add, would not be appropriate today - it would only suit a more "intimate build".

Building with cob, she says, requires "good boots and a good hat" - for the building. The foundations should drain well to keep water from attacking the base of the walls, and the upper surfaces of the walls need to be protected by a roof of some kind such as thatch or shingle. The Anglo-Saxons were masters of this sort of building and traces of Anglo Saxon and iron age buildings such as roundhouses have been found close to the site we are going to build on. One of the marks of a roundhouse is the erosion created by rain dripping from the circular eaves.

Glen and Mary arrive and we can have the safety briefing that had to wait for their presence. Their teenage children were supposed to come as well, but apparently could not be persuaded to venture out on a bank holiday morning. We pick some stout gloves and head off to the site to start cobbing.

The site is part of the University Farm, which has been pressed into service for the huge building project of houses, a school and a community centre. Glen has been involved in the planning process and knows a great deal about how the new site will work - its bus routes, a high speed cycle network, and the relationship between the university development and privately funded housing developments.

There is a white portacabin on top of a rise and great signs of moved earth around us in heaps and  ridges above a flattened excavated  plateau. Some of these heaps - the topsoil - are growing weeds, while the gravelly subsoil which consists of sands and flinty gravels with a little clay has very little growing on it. This is the principle ingredient of the cob.

We collect some subsoil in wheelbarrows, cointing the shovel loads, put in the right amount of sand, and wheel it towards  tarpaulins where we mix in straw and water, then do our first "cob dancing" - treading on the mixture till it achieves the right consistency, which Karen says should be "like dinosaur poo". Rolling the mixture in the tarpaulin - a technique apparently developed in the US - we mix it further, then keep trampling, and trampling. We try a "drop test" - making a cannoball-sized sphere of cob and dropping it from waist height to see if it "splodges" in the right way, neither crumbling nor splatting flat like a soggy cow pat. It splodges nicely, though it is a bit soggy at first - more subsoil is mixed in. To get the feel of working with cob we each create a simple "maker's symbol", a small cob sculpture that will go into the finished artwork.

We wheel the mixture down to where the results of the previous week's cobbing - the first week of the enterprise - stand, in magnificent geometrical blocks, on the cleared building area shared with the archaeological survey. The areas for cobbing are marked out with plastic pegs, and those for archaeology with nails and string. Apparently the archaeologists got cross last week because some of the nails got moved. We try not to move any.

We set to work on 1:12 models of a row of houses. This is actually quite a large scale - the walls of each completed house reach 45cm-high, and the pitched roofs will take them 30 cm higher still. Each has been built with about seven successive layers of cob, with each layer allowed to dry fairly firm before the next is built. This is a time-consuming process. Each house has been started by packing cob into a former the shape of the base of the house and continuing upwards. We continue the work, packing the cob in closely with gloved hans and shaping it with plasterer's finishing trowels. Some of the flints in the nearby grvel turn out to be better than our increasingly battered fingers for pressing in the cob tightly. We are off! This is where we get to grips with the texture of cob and its behaviour as we try to shape it.

The days work is only interrupted by an excellent lunch of salad and cheese back at the barn, prepared by the jovial Al and his partner Cindy, and drinks at tea-time. At lunch time Shaun tells us how Nicola Tesla's plans for inexpensive energy are now being widely publicised on the internet, and can be downloaded and implemented cheaply, provided the opponents of this sort of thing don't get to you first. "Sounds like a bit of a conspiracy theory" says Kirsten wryly, and Shaun happily agrees. "It is! It's a massive conspiracy, but when thousands of people know how to do it then they can't keep it a secret any more!"

Over the afternoon we work away steadily, the buildings rising slowly and carefully. We can see that a hastily built wall constructede the previous week has fallen down. "They built it too daintily", says Kirsten, and we try to build with suitably contrasting vigour and determination. There is a lot of laughter, particularly from Li, who finds much to laugh about while continuing to speculate on the possibility of quietly building a house in a modest corner of Cambridgeshire. Glen the planning official is sceptical in a friendly sort of way. Li would include lots of pebble spirals as decoration. "Very auspicious! Very, very auspicious!".

The afternoon passes amazingly quickly and huge amounts of cob are consumed by the model buildings. We are using bricks as fillers to bulk out the solid cob forms. We pack up in a fairly organised way, dividing equiment into wheelbarrows,  and back in the barn Karen tells us about cob buildings she has made and shows us some recent artwork - ceramic loaves that elegantly make the connection between bread-making and ceramics. The word "cob" is linked to the old name for a loaf. The ceramic loaves look a lot more edible than the lumps of cob, but I am already developing an affection for this ancient form of building.

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