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My first cob building  RSS feed

 
Kate Vin
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Hey everyone!
I am new to the forum, and I signed up hoping to share thoughts and experiences about natural buildings.
I  live in France and I have a kitchen garden with veggies and lots of herbs. I have a dog, three cats, 2 horses and many ducks, and oh, a husband!!!
I am a girl, but I do love to do all manners of non-girly things like building
I really am the builder here, although sometimes I can convince hubby to lift heavy stuff for me.
I am Kate; Vin is my favourite crowbar. We work wonders together.

Last year I started building a tiny cob shed, with the idea of learning the tecniques and materials for a future cottage (a tiny cottage, on the footprint of an ancient ruin we have on our land).
Late in the autumn I dug a foundation trench, as far down as I could, until I reached stone or really hard clay. In this spot, it makes for a prettz shallow foundation (more about that later). I made sure the foundation bottom slopes a little bit downhill so it serves as drainage too. Then I planted posts and built a reciprocal roof on the posts. All the timber came from our forest. They were all poles of chestnut that died on its feet. When I peeled the bark (with an old 2-handled drawknife, an invaluable tool), I could tell if the wood was too dicey (off to the stove!) or sound (up to the roof!).

There are several tutorials online onhow to build thiskind of roof. A small roof like mine (about 4 m across including the eaves) is dead easy to build, even alone.

The foundation was filled with small stones/gravel, and tamped hard.
Note that hereabouts we hardly ever have serious frosts (well, frost yes, but not to freeze the ground to any depth, really) and no earthquakes at all. So you can get away with very simple foundations. Even the old stone houses here don't have really much in the way of foundations, according to a friend of mine here who is a builder! In more difficult areas you will need more robust foundations.

Well, the stemwall was built with local stone around the posts. These are somewhat crappy stones, the good ones I kept for the cottage. The stones were stacked dry and then "mortared" with clay and sand, inside and out. The middle of the wall remains free draining.

This shed is just 2 m across inside (more or less round), but I made the walls 45 cm thick, so I could have shelves built into the volume of the walls (brilliant if you need to keep the floor area down!)

Over the reciprocal frame I made a ceiling of salvaged planks (this is where hubby came handy, to saw all those bits of planks!, oof!).
Over this I laid:
a vapour barrier (plastic sheet),
then lots of straw (not that insulation is much of an issue with this open shed, but it evens out the shape of the roof),
then lots of old sheets, recycled (to protect the waterproof membrane from the spiky straw ends),
then the waterproof membrane (2 layers of sturdy plastic sheet... pond liner much better for larger roofs!) with rain-spouts going from it through the eaves of the roof (more about that later)
then some rot-resistant polyestere fabrics, recycled (old parasols, and gazebo covers) to protect the mebrane from spiky things in the soil,
then the skylight (not glass, I am afraid of falling branches, but greenhouse plastic)
then topsoil mixed with old hay. The hay made the soil "fibrous" and helped it stick together when the roots of the plants had not developed yet.

This shed is in a lot of shade in summer so sedums and grass didn't seem a good choice. I planted a bunch of creeping things from the garden and forest,and it was a surprising success. In less than a year the roof really exploded with greenery. Species on my roof:
Ivy (hedera)
lesser periwinkle (vinca minor) (v.major would do to too, but it's such a thug!)
Bugloss (ajuga reptans)
lamiums (various)
ferns (various)
mosses (various)
strawberry (fragaria ananassa)
geranium machrorhyzum
potentilla quinquefolium
creeping charlie (glechoma hederacea)
sempervivums and wild sedums (these are suffering from the shade in summer, but they look good in winter)
*Geranium robertsiae* (herb robert: this I didn't plant, the seeds were in the forest topsoil: it went rampant and is glorious. Next spring the roof will be a pink cloud!) I definitely recommend this plant for similar conditions.
various grasses that came up from the hay including a few sprigs of barley!
various weeds and things that sprouted from the topsoil from seed.

All these things were planted in december (we have pretty mild winters) and were well rooted by the end of spring. Despite the appaling drought we are having, the roof remained green with only minimal watering. Maybe 5 or 6 times during the whole summer, for a couple o f minutes, with the hose.

The shed was left alone for the rest of the winter, while I worked on the future cottage stemwall beside it, and dug up lots and lots and lots, no, really LOTS of clay.

Ok, part 2 will follow soon, I promise.

You can see some pics here:
https://www.flickr.com/photos/mihara-kokonoe-tama/albums/72157685657647094
I will try to add more, especially of the early phases!
 
Kate Vin
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Ok, part two started at the end of May.

First, I laid a plastic sheet over the "floor"of the hut.Then I filled it with a cob mix of clay sand and longstraw, tamped it down carefully and left it to dry for a few days.

I would have much preferred to lay the cob on a layer of gravel, without the plastic (I am more worried of water puddling in from the top of the floor than water seeping through from under) but carrying gravel to this site is nearly impossible, so...
This was my first attempt at cob mixing and it nearly was the death of me. I quickly realized that turning cob with a fork in a pit is not for me.
When I started the walls I switched to the tarp system, and this is much much easier. I started with very small batches and worked my way up. Soaking my clay in buckets, and mixing it by foot in the tarp, is by far the best way for me. The tarp sits ina shallow pit, so the clay remains well bunched. I didn't screen the clay for the general purpose cob. Any larger stone that made it's way into it, I'd feel it my feet (ouch!) and fish it out. I made a routine of threading very slowly at the beginning, to test the batch for stones, glass and pottery shards. Once the whole mass is threaded properly once or twice, I can pick up the rhythm (depending on the energy levels). Once a batch of cob is ready for building I break off clumps of it with a fork and plop every clump in front of the building. This is easier than trying to pry gobs of cob from the mass with your hands, although it does have a tandency to steal straw from the bottom of the mass of cob. So you get some gobs of almost pure clay at the bottom, but those come handy to finish off the surface of coarser cobs, glue them together etc. In time you get to know which cob is good for what

I did all the cobbing alone, which can be tedious at times. Music definitely helps. The Chieftains' Rocky Road to Dublin is much the best cobbing song I discovered so far

I am lucky to have the perfect sandy clay for cob. If I soak it in buckets, by the time a batch of 4 20l buckets has been treaded and built into the walls, the next batch is soaked ready for treading, and so there is a good rhythm. The clay was soaked but not "liquid". Just enough to model it and make it stick together. More water can always be added while treading.

By working alone a few hours a day (I have animals to tend, a garden, and a houshold to keep going!) it took me about 2 months to build the cob walls of the shed.
Building around the post and beam structure can be fiddly in parts. The idea was to build the roof first to protect the unfinished walls from the rains. It goes without saying that we had no rain whatsoever in all the time I was cobbing. But if I had not built the roof first we would have had 2 monsoons in a row, I am sure. It is what C. Lloyd called the natural cussedness of things.

Well, in this shed I took the chance to try out different kinds of shapes of doors and windows. I much recommed pointy gothic arches, if you have the height for them. They are much easier to build than lower arches, because each course of cob projects only a little from the edge of the course below. In this way you hardly need to make "corbel cobs" as they are called in "The Hand Sculped House" (a book I can't recommend enough). Corbel cobs are made with lots of straw stalks laid parallel in the clay. They are very strong, and fun to use, but time consuming to prepare. Gothic arches are also stronger.
Lots of shapes were sculpted in the clay, again to try out the possibilities. The scupted parts are made of slightly finer cob. I was more careful to extract stones from the clay, even smallish ones, and made sure to discard the more stiff straw stalks, or using the wispy, crushed straw that collected under the bale as I extracted the big flakes for the normal cob. But I never actually screened the clay until I started the plaster, stucco, and floor.

I walled a mirror into the cob simply by standing it between two large blobs of cob and then building around it, and included several sturdy planks as shelves and windowsills.
I noticed that it is much better to put a couple of narrow planks the same thickness as the future windowsill as "place holders" where the edges of the windowsill will be built into the walls, while you cob. Once the cob is alrealy dried out quite a bit, you knock the place-holders out and bang the sill in, by slipping it in sideways. In this way the wood does not soak up all the humidity from the cob and does not warp. I made one sill with this sistem (perfect!) and one by simply laying the sill in the cob and then building around it (a disaster, never again!). Ofcourse this will not be possibleif you needto build in the window-frame ontopof the sill...

Well, once the cob walls were all done I trimmed out the most outrageous bulges, filled up some ugly dimples, snipped off the longer straw that stuck out and made the plaster/stucco. Oh, I tryed using a machete for trimming, but in fact I much prefer an old saw with a very flexible blade.
Plaster/stucco I made by using screened clay (very fluid, like pancake batter), mixed with screened dry horse manure (tiny hay fibres!) and some fine sand.
I made the cob walls wet with the hose, and smeared the stucco on with my hands. Once the stucco is "set" but not dry, I smoothed it with a wet (very wet) brush (actually a broom without a handle). Once it was completely dry, I brushed it again gently with the same broom, dry, to dislodge the looser bits. This leaves a pretty surface.
The idea was to paint the interior with natural limewash... But I do love the colour of the clay. We'll see.
Oh, the ceiling of recycled planks looked a bit shabby, so I decided to plaster it with the same mix. It is a bit tricky to get the plaster to stick to the wood, but once you get it to stick it stays stuck, so it's worth the effort. In some narrow nooks and crannies at the top of the roof I used a thicker mix (thick enough that it could be modelled into little balls) and it was actually rather easier.

The clay floor is not finished yet, so That will be part three.

As always, photos are here:

https://www.flickr.com/photos/mihara-kokonoe-tama/sets/72157685657647094
 
r ranson
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That's a great project. Absolutely beautiful!

You can also upload your photos directly into your posts.  I noticed a lot of photo hosts seem to make the images available for only a short time.  This way, it's forever and it doesn't cost you anything.

Absolutely brilliant project.  Thanks for sharing it.
 
Kate Vin
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Thank you so much!!
I am really super-motivated to start the bigger cottage now!
It was so much work to do this, but so rewarding too, and it is so beautiful there among the trees! Much prettier than any shed I've ever seen

I also want to say, I am a woman,and a pretty small one too, but I was able to build this practically on my own, so I encourage people to give this a go even if you don't have a big bunch of brawny builders at hand

There should be no problem with the pics disappearing, I have been on Flickr for ages. Unless all of flickr goes belly-up of course (fingers crossed!)!
I thought I'd put them there so I can send the link also to my friends
 
Martha June
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Location: Southwestern Ontario, zone 5
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Thanks so much for posting your building steps and photos. Your cob shed is beautiful. Really amazing - from the roof through the wall shelves to the finished form. Your postings give me hope that I can possibly do something similar - I also am a woman and I would like to build a structure with cob. I live in a Canadian city with building codes which I'll have to check out. But I'm enthused to start some small project - maybe a playhouse for my granddaughter.
 
Kim Arnold
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You are definitely a cob artist! That's a beautiful structure. Can't wait to see your cottage!
 
Kate Vin
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Thank you very much for your comments on my little building!

The cottage won't probably be finished for two years at least, gasp, and then it will need a little extension to one side to be really comfy. Because it is built on the footprint of an old ruin it is practically a square building (gasp!! the horror!) so I want to build a rounded extension to help it blend into the surroundings.
I really like the curvy aspect of cob building, it looks so organical and natural (which it is, of course!).

Martha, of course you need to check with the local regulations, but in many places very tiny buildings can be built without permissions, so a play house or shed could probably be built without burocratic entanglements (that is the case with my little shed). If you want to give it a go, I'd be happy to help with any little wisdom I accrued, but really I recommend Ianto Evan's book "The hand-sculpted house"! It is a wonderful book to read, and a positive mine of information.

I found this tutorial for reciprocal roof building very useful: http://www.thatroundhouse.info/reciframes.htm
I might add that when building a very small roof with relatively light rafters you can get away with very little measuring and marking, as it is very easy to adjust things as you go. On a larger roof, that is probably not possible.

Today after much heavy work I decided to reward myself with a little artistic fun, so I will post some new pics soon

Thank you again for your positive feedback, it really means a lot after all that work!
 
Julia Winter
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Your cottage is lovely, thanks for sharing! 

Thanks for sharing the link about reciprocal roof building.  I have been struck by the organic beauty of that sort of roof for ages, but didn't know what they were called. 
 
Tiffaney Dex
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Hello Kate. Your buildings are absolutely beautiful! I admire you for it. At my house, my husband is the one who accomplishes things like that, while I take the typical female role. I admire you for all of your hard work.

What part of France do you live in, since you do not freeze very much? My family and I live in Brittany, so not much on freezes, either.

Take care.

-- Tiffaney
 
Kate Vin
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Hello there, and thanks! I live in the Dordogne, so we get frosty nights in winter, but this site is on a south facing slope, so it's pretty mild!


I had some fun with clay plaster (well deserved after all the heavy work, right?). It will be prettier once the clay is dry and blend in the wall.
Fungo-hut-dragon.JPG
[Thumbnail for Fungo-hut-dragon.JPG]
A bit of fun after all the hard work. Freshly modelled dragon on cob building.
 
Tiffaney Dex
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That is an area where I have never been. From what little I do know, your tomatoes don't succumb to mildew. Is that correct?
 
Kate Vin
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It really depends. For several years we had no great trouble with mildew. Then last year it was a disaster. This year is not so bad, but it's been so dry that everything struggled quite a lot. Maybe even the mildew gave up!
 
No prison can hold Chairface Chippendale. And on a totally different topic ... my stuff:
The $50 and Up Underground House Book by Mike Oehler - digital download
https://permies.com/wiki/23442/digital-market/digital-market/Underground-House-Book-Mike-Oehler
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