LESSBIG attended 1 day of a 2 day course, run by The Society for the Protection of Ancient Buildings (SPAB) in Slawston, Leicestershire on the 30th of April. There were a number of very informative talks and some hands-on repairs of an earth walled stable block.
Adults go off for a tea break – kids swarm in for some muddy fun
Read on for lots more pics and notes:
First of all, the talks
Rather than risk getting people mixed up, I’ll just list some of the factoids that stuck with me and say they all came from these three speakers:. Jason Mordan, Nottinghamshire County Council; Stafford Holmes, Architect; Anthony Goode, Conservation Builder and during a tea break, Jenny Clarke and John Acres shared their experience of undertaking repair on one of their mud walls.
Anyway… facts away!
– The Geology of Britain viewer is an interesting (if a bit difficult for the newcomer) online map through which you can see the different types of stone and minerals beneath your feet. From this we can see why certain areas took to earth building more than others, it depends on whats available of course. Also things like Earthquakes and Boreholes.
– An earth built dovecote in Flintham, Nottinghamshire was featured on an episode of Countryfile. (Sorry I can’t find any pics, but here’s a link to the ancient monument scheduling). It was partially at threat because of Ivy growing on the top; ironically, the ivy may have been planted there back when it was originally built in order to act as a roof for the structure.
– The ICSEAH (International Scientific Committee on Earthen Architectural Heritage) continue to host a number of conferences around the world. (next one is in Korea, any one happen to be in that neck of the woods? ;) Their website is worth a visit, the ‘Terra’ conferences I had heard mentioned a few times but it’s a shame I can’t seem to find much more about them online.
– The work of HANDS (an NGO in Pakistan) who, amongst other things, have helped rebuilding after the 2010 floods. The benefits of earth being relatively easy, cheap and low tech to work with; which helps ensure that it can be maintained, repaired and rebuilt by the people working there. It’s easy to turn to cement thinking it will be stronger, but it’s heavy and costly to ship and repair.
– Cement and earth are not best of friends as, generally speaking, earth ‘breathes’ and cement doesn’t. There are numerous examples of a cement render being applied to fix an older earth wall, where, over time, the render will ‘balloon’ out and fall off.
– Some other random characteristics to be aware of; it’s possible to compress a drier mix more than a wet mix; the higher the clay content, the more shrinkage is likely to occur; you might think a cement mixer might be a good idea for mixing earth and straw but in practice it just bunches up.
– Barley straw is thought to be preferable for cob as its coarser texture helps grip the mud, whereas the smoother Wheat straw can be preferred for roof thatching; if not using some kind of reed.
– And finally, the Mosque of Djenne in Mali. One of the most impressive earth buildings standing in the world. The current structure was actually finished in 1907, so more recent than you might think at first glance (link)
Now the messy stuff… the cob wall, the bricks and the rammed earth wall.
Hands-on Part 1: The Cob Wall
The length of the wall before we started to make repairs. The holes ranged from tennis ball sized chunks to smaller bee holes.
The wall needed to be wet to help the new mud stick, so a quick spray of water also encouraged the bees to move on. Structurally, the bees don’t really go deep enough to do any major damage.
A close up of a repaired section. I would have taken a photo of us ‘at work’ but its pretty messy work! Essentially you just press the mix into the holes, with a bit of stone or premade cob block if it’s a particularly large gap. Got to give it a bit of a chuck to get deep into the holes.
These mixing trays were pretty handy but we also just used any piece of flat wood. The dirt had already been sieved for larger stones, organic material. I think a little sand was added too but this might vary on the composition of dirt being used.
Water of course, add sparingly. You can always add more. This mix (for repairing the wall) was fairly wet in order to get into the holes. Other applications were drier, which we’ll get onto in a sec.
We added hay to this one. Again, straw was used in other applications but the fine consistency of the hay helped a bit for the repair work.
Just a shot of the mix ‘nearly done’ at this stage, having been turned by spade and trodden down several times to get it all well mixed and bound together.
This is roughly where we were by midday, quite a lot of progress I think.
Hands-on Part 2: The Bricks
A range of bricks drying out. The kids who came at lunchtime were pretty productive!
The brick molds we used. Note the removable slats for making various sizes or multiple sizes. These should be wet before you pack the mix in.
Fill up the mould, pack it down then lift away (handles on both sides) However…
…this particular mix was too wet. The bricks would not separate from each other. Also they would probably take ages to dry and couldn’t really be moved without falling apart.
Here’s another attempt with a one-brick mould and a drier mix. Trimming and scraping was a fair task as well, if you wanted them to look as smart and uniform as possible.
Evenly removing the mould while applying pressure to the top
A much more consistent looking brick (with the shoddy one nearby for comparison!)
It can even stand up on end without collapsing! Success.
Hands-on Part 3: The Rammed Earth Wall
This frame is holding up/together a small rammed earth wall that was being built from scratch. The consistency of earth being used was much drier, with no straw/hay being added at this stage. You pile up the earth inside, then ram/stamp it down for quite a while! I believe the general rule of thumb is that the earth will compress about 3:1 – so although the wall looks fairly small, roughly 3 times that volume of earth has gone into it. Go and look up pise / rammed earth walls. The finished product is pretty amazing. Note it is still raised off the ground with a stone foundation/plinth.
A roof was being added at this stage, with a cob mix being used to help anchor each roof truss. Note the fairly wide pitch of the roof; this will help throw rainwater far from the wall.
There were four trusses overall. Getting them level seemed tricky, but given the cob was easy to move around it was possible to fiddle them around quite a bit until it was right. This was going to be finished on the second day. I will see if I can get a picture.
You can read more about the whole course from one of SPABs own team here (link)
The finished wall eventually looked like this, what a beaut:
image: Alex Gibbons – SPAB
Lots to keep reading in the delegate pack and free copy of Cob Buildings by Schofield & Smallcombe (Black Dog Press.co.uk)
Thanks once again to SPAB for this fun, informative and well organised day, and a special thanks to Anthony Goode, the East Midlands local ‘mud man’!
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