Adobe Buildings - How They Are Constructed

Construction of adobe buildings can be traced back to 500BC, and the method of construction has changed little during the intervening 2000 years or so, except that nowadays, the adobe mixture can have asphalt added and then be hydraulically pressed into brick molds. But the traditional method of packing the mix into the brick molds by hand is still widely used and a more satisfying method.

The brick molds are usually made from wood, to the required size of the brick.

The components comprising of clay, sand, straw and animal dung are mixed with the water then packed into the mold, ensuring that all the air has been pressed out of the mix. Once this has set, the mold is removed leaving a formed adobe brick, which will be left for up to a week to harden, depending on the weather.

Once sufficient quantities of bricks have been prepared, (a single storey house can require 6,000 bricks) the construction of the building walls can be commenced.

The bricks are laid in the traditional fashion known as a running bond, the mortar being made from the same mix as the bricks, but of a more watery consistency and without the straw component. The foundations can comprise of poured concrete or the traditional method of footing which is to compress the earth to support the weight of the walls above it.

This is the fourth in a series of articles on natural green materials for buildings, the previous ones being on straw, logs and rammed earth.

As with the previous articles, the descriptions and method used for the buildings is to illustrate the aesthetic quality, durability and suitability of the material, and not to be used as a technical construction manual.

We shall begin with the components of the mixture used when building with adobe.

The components of the usual mix are as follows,

• Clay – The mixture contains about 50% clay, bonding the material components together, and the clay used should be able to pass the following simple sediment test:

-A handful of clay is added to a glass jar of water and vigorously shook until the contents are well mixed. It is then left for an hour or so on a level surface. Upon examination, the water should not be cloudy; the clay lying at the bottom of the water indicating the clay is suitable for brick formation. A cloudy mixture indicates clay which would produce weak inferior bricks, liable to crack.

• Sand – 30% of the mixture is ordinary sand. This is used to bulk out the mixture acting as a filler to the mix and bonding to the clay.
• Dung or Straw - This makes up the last 10% of the mixture, and either one can be used as a bonding agent. I wondered about the straw used for bedding for cattle in barns, this would be a combination of both. But I am sure the dung would need to be dried before use so it crumbles into the other mixtures. The straw or dung is used to strengthen the bricks and help dry them out evenly avoiding cracking or crumbling.

Note

These percentages vary for different countries, for instance adobe building construction companies in Canada recommend up to 70% soil content in the mix.

A typical frame mold measures about 10" x 14" and is made from 6" x 4" sections of wood, but these dimensions can be altered to suit the size of bricks required. The frame is laid on a firm, level plane where the mix is shoveled into it and tamped down until level with the top of the wood frame. This ensures all the unnecessary air and water is expelled.

After a short time, the frame is removed and the formed brick left in the sun to dry for a few hours. Once set enough to lift, the bricks are brought into shade for final drying, lying on their side. It takes about a week in the hot weather for the bricks to harden and be ready for the wall construction. A DIY family can produce 200 bricks per week. (Why not have a few brick building parties or barbeque parties – where everyone constructs 20 bricks!) Remember to have plenty of mixture and molds ready.

Please read on to find out more about adobe building construction methods.