Dr Bob Rich
Mudsmith
Frequently Asked Questions
1. But what happens if it rains?
You come in, and look at the rain through the window! A properly built, earth-walled house is weather-proof, and resistant to weather damage. If you want to know what 'properly built' means, read the Earth Garden Building Book .
There is a rammed earth barn in the south of England that is over 400 years old. The roof burnt down 80 years ago, and was never repaired. The walls are still standing (they probably have a high content of lime).
The temples of Angkor Wat stand in the junge, in a very high-rainfall, tropical area. The earth walls, which receive constant maintenance, have been standing for hundreds of years.
Sennacherib built his great city of Nineveh in about 700 BC. Complete, undamaged mudbrick (adobe) buildings have been excavated. They have been lying underground, buried in sand, for 2700 years!
On the loess plains of China, people build endless mudbrick windbreaks that stand out in the open for many years. The top of the wall is sloped so that rainwater runs off, and they make a thatch from grass as a little roof.
I have often built experimental earth walls, trying out different techniques and materials. The wall is left out in the open, completely exposed to the weather. The poorest wall stood up to two wet winters before collapsing in a storm. The best stood there for five years without appreciable damage.
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2. Is it cheaper to use mudbricks?
Depends on what you define as a 'cost'. A CSIRO study showed that if you cost all materials and all labor, and do all work on site (no prefabricated components), a mudbrick house and a brick veneer house of the same size and design will cost exactly the same.
Mudbricks have a very high labor content. Rammed earth (pise) and poured earth (formwork cob) are much more efficient techniques. Depending on circumstances, they need between one-half to one-fifth of the labor content per volume of wall. Therefore, even if you pay for all labour, a rammed earth or poured earth house is cheaper than a brick veneer.
If you do some or all of the work yourself, you can trade off between time and cash. My house cost me $10,000 for materials, and nothing for labour (though I bartered work in various ways). Others have built even cheaper. Mudbricks are cheaper than other earth building techniques. Rammed earth often needs cement, and even a small proportion like 5% adds up when you build a whole house with 12 inch thick walls. Poured earth using sandly soil needs even more cement. Both these techniques need formwork, which also costs money.
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3. What is better, adobe or pise?
Currently, I am displaying a section from the
Earth Garden Building Book
discussing this issue.
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4. How much can I expect to pay for suitable soil?
Nothing.
Low environmental cost is one of the benefits of building with earth, provided you use the soil right there, on the site. Middleton, in
Build your House of Earth
estimated that all the exterior and interor walls of a mudbrick house can be built from six inches of soil removed from the site. Levelling a slightly sloping site will give you more than enough raw material for the walls, provided you don't mix up different layers. Or you can excavate a hole for an in-ground swimming pool.
Soil is heavy. Carting it around converts fossil fuel into air pollution.
A suitable technique can be found or developed for
ANY
soil.
Of course, building with some soils is very hard work. If your building block has heavy, sticky alluvial clay, your mudbricks will be excellent but making them may wear you out. The solution might be to sell the block and buy elsewhere. This is better than carting many tons of stuff. Or you can reduce the labour content and difficulty through ingenuity, for example
The
Earth Garden Building Book
has many such ideas, and you will find even more in back issues of
EARTH GARDEN
magazine.
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5. Are earth walls good insulation?
No.
Thermal insulation uses one of two processes.
Reflective foil
bounces electromagnetic radiation back instead of letting it pass through or absorbing it. It must have a 1 cm (half-inch) air gap next to the shiny surface, or it won't work. A double-sided sheet of 'RFL' with an air gap on each side and no dust on it has an insulating value of 'R1.5'.
Bulk insulation
works by trapping air. What traps the air is immaterial. Fibreglass and rockwool are the usual, which is a pity because they have very high energy costs of manufacture.
ANY
fireproof substance will do: scrap wool or shredded paper treated with a borax-based mix are examples. A one inch layer of bulk insulation has a value of R1.5.
A 12 inch thick earth wall has perhaps one-third of the insulating value of double-sided, properly installed RFL.
Nevertheless, an earth-walled house can be cool in summer, easy to heat in winter, at least in the range of climates found in non-tropical Australia, and in desert regions. This is because the
thermal mass
of the solid walls evens out temperature fluctuations. (Thermal mass works like a hot water bottle.)
In places with very cold winters, eg., in much of North America, a cavity wall would seem to be essential: two walls close together, enclosing a (say) two-inch thick air space. Insulation can be placed within this cavity.
Trapping air within the earth wall enormously improves its insulating properties, without sacrificing thermal mass. I have built a poured earth wall where I enclosed empty bottles within the mix. About half the volume of the wall is air. The result is an ideal mix of insulation and heat storage.
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6. What is 'poured earth'?
The
Earth Builder's Handbook
(available from
EARTH GARDEN
magazine) contains a description. The technical name for 'poured earth' is
formwork cob
, and it is discussed under that heading in the
Earth Garden Building Book
. Several back issues of Earth Garden magazine have relevant articles, and one has appeared in
OWNER BUILDER
magazine.
Poured earth can be done with any kind of soil, but the technique has to be adapted.
Clay soils
In effect, you make mudbricks directly on the wall. The layer you pour almost welds to the previous layer, and need never be moved again. It dries perhaps three times as fast as mudbricks, because the moisture soaks into the wall below the current layer. You should go up in 6 to 8 inch (150 to 200 mm) rises. The formwork can be relatively flimsy as long as it is well braced at regular intervals. Cut the mud with a trowel, or insert temporary dividers, at approximately mudbrick-length intervals, staggering these from course to course.
Sandy soils
You can go up in rises as high as is convenient, though the higher you go in one step, the stronger your formwork needs to be (to resist hydrostatic pressure). The mud can be mixed in a cement mixer. You need to add cement (determine the proportion through small-scale experimental samples). In effect, you are making a half-strength concrete wall. Do not make the concrete too strong, because then you are reducing thermal insulation and make a hard, sound-bouncing surface that is not nice to live with. Use the
lowest
cement content that gives a durable wall. The test is: Let the wall cure for at least two weeks, even longer if possible. Then scratch it hard with a metal object like a nail. You should not be able to gouge out to more than a quarter inch (6 mm) depth.
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7. How do you build a house from
straw bales?
I have never been involved in building a strawbale house, though I've read books and seen demonstrations.
A systematic, detailed description is given by
Huff'n'Puff Constructions
strawbale.archinet.com.au/build.htm
, an Australian company. This is almost a mini-textbook on the technique, illustrated with excellent photographs.
The definitive list of links relating to strawbale construction is at
Strawbale Construction in the Colorado Rockies
www.moxvox.com/straw.htm
.
My only additions are:
a) Straw and hay are different. Hay rots far more readily. You can't build with it.
b)
Keep your straw bales dry at all times
. Every precaution must be made for this.
c) It is environmentally unfriendly to transport bales over a long distance. Use the source closest to you.
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