Dr Robert Rich
MUDSMITH
Author of the
Earth Garden Building Book:
Design and Build Your Own House
[by Dr Robert Rich & Keith Smith; 4th ed. Viking 2005]

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A Short Sample [pp 106 - 107]

Rammed earth (pise) versus mudbrick (adobe)
    These two techniques use different types of soil (See Any soil will do, page 95).
    It is silly to decide on a building technique in the abstract and then to have to buy and transport the materials for it. It is better to adapt the technique to the soil on the site. Nevertheless, the most frequent question asked about rammed earth is: 'How does it compare with mudbrick?' Here is a comparison.
Advantages of rammed earth
*     Other things being equal, rammed earth is about half as labour intensive as mudbrick. There are two reasons for this.
    First, rammed earth is a means of constructing the wall in place. Any such monolithic technique involves less work than the making and combining of materials. Mudbricks have to be made (mixed and shovelled into forms), handled several times during drying (stacked and turned), even perhaps stored and later removed from storage, transported to the job and laid with mortar mixed for the purpose. Rammed earth involves preparing and transporting the soil only once. The soil may have to be sifted and cement will probably need to be mixed in, but then the soil is shovelled into forms (or poured from a bucket), rammed, and there you are, with a completed piece of wall.
    Second, ramming soil is used just damp, not wet and sticky. Mixing and handling wet soil is much harder work than anything you need to do when ramming.

*    Rammed earth doesn't shrink. There are no worries with cracking, no gaps at the top or next to doors and windows. It is true that insufficiently compacted rammed earth tends to powder away. This can usually be repaired (see Preparation for rendering on page 153) but it is a problem that's best avoided.
*    There is a limit to how many courses of bricks, stone or mudbricks a person can lay in one day. Too much, and the still-soft mortar gets squeezed out. There is no such limit with rammed earth. I have seen a team of eight people complete a 4 metre long, 3 metre high wall on a single day (this wall was three sections long and five sections high).
*    Mudbrick making and mortar mixing require a lot of water. Ramming needs only a little. This can be a big advantage if water is in short supply or has to be brought in by drums or buckets.
    Mudbricks take time to 'cure' before they can be moved. This means that you need either a lot of flat space under cover, or you will have to spend extra time covering and uncovering the bricks as they dry. There are no such space problems with rammed earth.
Advantages of mudbricks
*    Mudbricks (and compressed earth blocks) can be made in advance, for example while your house plans are still being drawn up. In this way you can put 'labour in the bank'. You could also employ a number of helpers by having some people make mudbricks while others are laying them. Rammed earth requires a small, practised team.
*    Rammed earth usually requires the addition of cement (average of 5%), while ramming forms must be strong and solid. You need money for both of these. In contrast, mudbricks can be made using a mould made up of scraps, and a bale of straw (if needed) will last for hundreds of bricks. So choose mudbricks if you are strong and have lots of time, but little money.
*    Mudbricks can be made in rainy weather, provided there is a flat area under cover. You may be brought to a standstill while ramming if rain over-wets your stockpile of soil, though soil dug out from a steep bank as needed will usually be dry enough.
 

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