This next session on the Earthship at Te Timatanga is all about Earth. Clay really to be more precise. Clay is like nothing else, a wonderful material that is very versatile, and in most places found on the site where you plan to build. With the right knowledge of subsoils, testing, combining, drying, application and sealing it can be a fantastic building material. Traditional Earthships use far more cement and less clay, but on this build we’re trying to keep it as natural as possible – being more environmentally friendly, cheaper, less toxic and just a nicer feel. Also its easy to use, the walls can regulate moisture, they are great sound barriers and they are amazing thermal mass (storage of heat).
So far, on this Earthship, we have used Cob for pack out, mudbricks for some internal walls, chip ‘n’ slip for others, and soon will be starting earthen renders on the walls. The upcoming session will be teaching a lot of these techniques, which will be a 2 week internship working on interiors of the ship. June 22nd – July 3rd.
Cob a very old technique for building with earth. Its the name given to the mixture of clay, aggregate and a binder, that is mixed (by foot, machinery or animal) and used primarily to build walls. It creates a very strong structure when it dries, and can be either load bearing (structural) or infill (between a post and beam structure).
“A cob cottage is the ultimate expression of ecological design. Made of the oldest, most available materials imaginable – earth, clay, sand, straw and water – cob houses are not only compatible with their surroundings, they ARE their surroundings, literally rising up from the earth. They are light, energy efficient, and cosy, with curved walls and built-in, whimsical touches.” Ianto Evens from Cob Cottage Company.
Mudbricks also use clay and straw, but in this technique they are made by pushing the mix into forms 270×270 (becoming 300mm walls with render) and letting the bricks dry. Bricks can be made faster and on a larger scale then cob, often made mechanically, and they are also faster to lay – a builder can lay up to 50 a day on straight walls. Mortar must be made for between each course and between each brick, about 20mm. In NZ we also use geo grid between every 3rd course, and 12 mm reo rods vertically that attach to the footings and join the vegas above. These mudbricks have been made previously in Golden Bay by Solid Earth and stored in the Coromandel, before being transported to site.
Building with earth is a very forgiving medium. If cob dries out, wet and remix. it the walls are splurging outward, saw it off. If the layer underneath is not smooth enough, wet and add another. It can be formed, sculpted, reshaped, changed and coaxed to your heart’s content. Renders are the usual way of finishing the internal walls of strawbale, cob, super adobe, mudbrick, rammed earth and earthship style houses. Three coats are usually applied, a shaping coat (the thickest – up to 10mm), brown coat (smoothing off, 3-6mm) and a final finish coat (2-3mm). Its is always a good idea to test your renders before applying, to get the right mix, which won’t be sandy (too much sand), or crack (too much clay). There is no straight recipe for this, as it depends on your soils, and your choice of binder, the usual mix would be 70% sharp sand, 30% clay (screened as you get to finer layers) and a binder of either chopped straw, wheat paste or casein. Poo optional . Tools vary too, depending on coat, the finish required and materials. Experiment and play are good teachers!
If you are interested in this internship, please email firstname.lastname@example.org and join us in June. Alternatively, if you are interested in Earth building of all sorts feel free to email me at email@example.com. I also hold earth building workshops, or can pass your details onto the right people!