Requiring no special equipment and no special expertise, and very economical to boot, earthbagging is famous as an ‘idiot-proof’ technique, popular with first-and-only-time owner-builders the world over. Venetia Kotamraju, who moved from busy Bangalore to a farm on the Western Ghats, writes on her experiment with earthbagging. The final installment in a series of four.
Venetia Kotamraju, Ecologise
It took us four weeks to build our two structures last year, and about eight months to plaster them, including the down-time monsoon months. Plaster in this context consists of mud; yes, more mud. Cement plaster on earthbags isn’t a good idea. It doesn’t allow the walls to breathe, and thus they tend to become soggy.
Mud plastering really is fun for all the family: stomping in the mud, hurling mud splats at the wall, smoothing mud-water over the bumps.
It is though, also, as we have come to realise, a fine art. We initially tried putting chicken mesh over the earthbags, as some experts recommend, and then plastering. That just resulted in baggy bits of mesh and fallen plaster. We tried numerous plastering recipes and methods, and have patchworked our walls with samples.
We burnt our hands, feet and faces when we added lime to the mix. And we even convinced the local mason, a cement-and-bricks man, to try doing a mud plaster.
We have learnt a few invaluable lessons:
– chicken mesh is a waste of time and material, and only creates problems – ditch it
– the classic combination of mud and sand, which many recommended to us, makes for a crumbly plaster which doesn’t stick; it also adds a real cost to the plaster because you need a fair amount of sand, so we now avoid it totally
– fibre seems to be vital; although some said straw here might cause termite issues we use it anyway (with cow dung to try and keep the termites away) because we haven’t found any better type of locally available fibre for holding the plaster together
– we add cow dung both for its fibre and also to keep away insects; in the West they tend to use Borax a lot (although perhaps this is more for mould than insects) and I imagine you could also try neem powder
– you need to apply each new layer before the layer below is totally dry, and you need to moisten it before applying so that they bond; plan your team and approach well to ensure that each fresh layer is applied at the right time (if you have a smaller team for instance and it’s hot, work on a smaller section so that you can apply coats two and three before the previous ones have dried out)
– flour/maida paste (the original glue or gum) seems to be the magic ingredient which makes the plaster really nice and sticky
– to ensure all is mixed well, use a tarp – stomp on the mix, then pick up the edges of the tarp and roll it into the centre; repeat, repeat, repeat
Here is the recipe we use (a modified version of Kalyan’s at ProtoVillage):
– 9 bandlis mud, 1 of cow dung, 3 of cut straw (about 2 inches), 1.5 cups of flour paste
– make the flour paste in advance: whisk maida with water; separately boil 10 litres of water and add the maida mix to it; keep stirring until it thickens into jelly; store in a bucket and use within a few days
– soak the mud in water a day in advance so that all the clay lumps dissolve
– mix the flour paste and cow dung thoroughly into the wet mud
– add straw bandli by bandli
We first fill the gaps to bring those sections level with the rest of the wall (lath layer), and then cover the rest of the wall. This forms the first layer. For the second layer we use the same recipe with either no straw or very little, and a little less cow dung, and apply it thinner and smoother. Then you are ready for the lime plaster:
We have also got a great lime plaster recipe thanks to Kalyan:
– filter sand through 4mm filter
– mix 1 part lime with 3 parts sand and enough water to make it into a paste
– add some jaggery and apply
He recommends mixing either with bullocks or in a cement mixer.
As we don’t have access to either, we do it with the good old gudli and so long as the proportions are correct (and we learnt the hard way what happens when you have too much sand – a crumbly mess that quickly disintegrates) it produces a good hard finish which we then paint with lime wash. To reduce the white dust this lime plaster often creates (leaving you with a white bottom whenever you sit on a whitewashed wall), you can add casein binder.
Heat milk and add lemon juice to make it curdle (as for paneer), and then take the strained milk solids and whisk with Borax to make a frothy mixture. Many people recommend curing lime plasters – keeping them moist for a week as you do with cement – and although we haven’t done this yet it is probably worth the extra effort.
If you have the mental energy to contemplate yet more mud and plaster work, you can also create amazing in-built furniture, frescoes, sculptures and other beautiful additions to your house using various types of mud and lime plaster, stained with natural colour, and sealed.
If you are building on a budget, beware the roof. Just as we were patting ourselves on the back for building two large structures with very little financial outgo, we came face to face with the reality of the roofs. After searching high and low for an affordable way to do it, we gave up and went with a steel-Mangalore tile combination which is the most durable and cost-effective solution in our wet climate, but not particularly sustainable (at least both steel and tiles are re-usable) and certainly not cheap.
We haven’t supported the roof on the walls of any of our structures, partly because of the special requirements of those buildings but also because we weren’t confident of their strength. That means a whole lot of extra steel pillars. There are certainly ways of integrating a roof into an earthbag structure but you do need to be very careful that the roof doesn’t push the walls out, especially in a round strucure, and in general I’d say get some expert advice before you try this.
Thatch might work in drier climates, as might bamboo. If you don’t treat bamboo properly though, you will be fighting insect infestations all the time. Wood seems to be so astronomically expensive in India that it’s probably no longer ever a viable option. And of course, if you have almost no rain you can try an earthbag dome which solves the problem of a roof altogether.
Surprisingly few earthbag resources talk about floors. Maybe people are so exhausted after the building and plastering that they just settle for a regular poured cement floor – and boy is it tempting. There are though other options. We’ve done jelly plus soil plus cow dung floors in several places. The massive advantage of these floors is that they soak away spills and don’t require any cleaning (bar the weekly reapplication of cow dung). The disadvantage is that they are bumpy and can be quite dusty, at least initially, and you don’t really feel like sitting directly on them.
This year we are experimenting with a sealed earthen floor, in which we create a 4 inch layer of jelly followed by an adobe mix (mud, sand, a bit of straw, cow dung) and then seal it with several coats of thinned linseed oil. You could also set tiles or large stones into the mud and then grout and seal.
Excluding tools and equipment, here is what we spent on constructing and plastering the earthbag walls of the building we worked on this year:
Our 10ft radius circle takes about 55 bags per course and we have four courses of jelly bags (which are double bagged so 55 x 4 x 2 = 440) and about 14 courses of earth bags (which are single bagged so 55 x 15 = 825), thus 1,265 in total. At Rs 6 per bag, that works out to Rs 7,590.
Other materials used:
– Quarry materials (boulders x 2 loads; 40mm jelly x 2 loads; baby jelly x 2 loads) = 17,500
– Sand (including for lime plastering) = 11,500
– Barbed wire = 4,602
– Nails = 1,218
– Steel tools (compass, slider, bag stand) = 2,745
– Wood and carpentry charges (for velcro strips, shelf brackets, arch forms and moulding tool, door frames) = 20,409
– JCB and tractor = 4,400
– Maida, jaggery = 1000
– Lime = 3,000
Total material cost: Rs 73,964
For the wall construction, we pay our team of 4-5 men Rs 300 per person per day and it took them about 30 working days, so Rs 1200-1500 a day for 30 days = Rs 40,500
For the plastering, we pay our team of 4-5 women Rs 250 per person per day and 1 man (to mix) Rs 300 a day for about 10 days, so Rs 1300 – 1550 a day for 10 days = Rs 14,250
Total labour cost: Rs 54,750
Earthbag construction is material-lite but labour-heavy. If you are doing this in a developed country where labour is relatively expensive, it isn’t nearly so cost-effective – unless of course you do it in a community or with a team of volunteers. We have had several visitors – friends, family, Workaway volunteers – join us for earthbagging, but, while it’s fun to have people participating, we have yet to find a single person who can last even one of our five-hour days lugging mud in the hot sun.
Earthbag Building – Kaki Hunter and Donald Kiffmeyer
The Mud Home: Earthbag Building – Atulya K Bingham
Earthbag Building in The Humid Tropics: Simple Structures – Patti Stouter
Soil Tests for Earthbag – Patti Stouter
Earthbags: A Primer in Self-Help Construction Using Flexible Form Rammed Earth – Sourabh Phadke
Videos on specific earthbag projects: http://greenhomebuilding.com/videos/earthbagvideos.htm
There are now several places where earthbag houses or huts have been built in India, including the visitor’s centre at ProtoVillage near Bangalore and other sites in Tamil Nadu, Maharastra and Rajasthan. Get in touch for more details.