| Handbook for building homes of earth |
Probably one of the first homes man lived in after he came out of a cave, was made of earth. To be sure, the earliest known kinds of earth construction were very crude by our standards today. Primitive man did little more than stick mud on poles woven closely together. But even with this, he found shelter that was better than anything else he had except his cave. He also had the advantage of being able to move around. He could live wherever he wanted to.
Gradually, he learned that some kinds of mud made better houses than others. And some of the best ones lasted his whole lifetime.
Today, there are plenty of earth dwellings in many parts of the world that are centuries old. Man discovered that the earth homes that have lasted best were in areas where not much rain falls. A wet climate is the worst enemy of an earth house..
Today, with the advances made in the science of soil mechanics, what soils will do under many different conditions can be predicted and controlled. It is possible, even with little skill, today to build beautiful, inexpensive and durable homes using the oldest construction material known, the earth around us.
Strangely enough, it is the scientific road builders who have learned most about the way many kinds of soil will behave under a wide variety of conditions. These scientists know, for example, how to take soils that for centuries were considered useless for anything and, by combining them with materials called stabilizers, make them into mixtures that are excellent for earth construction.
As in most important discoveries, this new knowledge, much of it learned since World War II, was found by work done in laboratories by highly trained technical men. It now remains to make these new techniques available to the people who need them most and can use them to their advantage: the many people in the world who need good, lasting homes and who cannot afford to spend a lot of money to buy them, or who do not have access to modern manufactured materials. Earth is everywhere.
One of the great aims of the Agency for International Development is to help fulfill this need. Under its Self-Help Program, which the AID feels gives the most help while allowing those aided to keep their dignity and pride, comes this manual as one of AID's many technical services.
This small book tries to take the newest techniques developed in modern soil mechanics and put them into simple terms so that almost anyone, anywhere, can have the benefit of the great amount of work that has been done by the scientists.
The AID authorized and paid for a research project by the Texas A&M Research Foundation, at College Station, Texas, to:
1. gather and study all available information on building homes with earth;
2. do new research in areas where not enough was known about what can be done with earth, and
3. bring this information together and present it in a form most useful for most people.
Information came from many countries and from all kinds of sources. These included books, articles, technical reports and even newspapers. More than 300 such sources were studied. In addition, soil engineers at Texas A&M University worked in their own laboratories and made tests of the materials they had and added the knowledge they developed themselves.
This manual tries to present its information in the simplest way possible. Because many things vary greatly even in one country, it is impossible to say all things to one person and have all that information apply to the place he lives.
The many kinds of climate that exist all over the world, plus the much greater number of kinds of soils that are found, make the problem of explaining just how to build a house difficult. For example, in the State of Texas, alone, what would be best to do in the eastern part would not be at all the same in the western part of the state. What would be fine in parts of the Rio Grande Valley and the Texas Gulf Coast in the south part would not be best in the Panhandle in the north.
So, this manual describes broadly the kinds of soil that are found in various parts of the world and tells what can be expected of them. It then tells what is best to do with each of them, alone or in combination with others, to make them good enough to use or make them better with the use of stabilizers. And then it explains which of the three general kinds of earth construction is best for use with the kinds of soil available. It also describes simple tests anyone can perform that tell the builder how well he is succeeding in what he is trying to do.
After chapters on picking out places to build, how to make a good foundation for any kind of house and how to build a roof, the manual has separate chapters on adobe, rammed earth and pressed block construction.
Because conditions and available materials change so much in different places, the builder often will want to use his own good judgment. It is therefore important, in order to get the best value out of this manual, that he read at least the early chapters carefully before deciding how best to solve his own problem.
As in any craft, the good workman has "the feel" of his job before he tries to go too far with it.
This manual, it is hoped, will give him that "feel."
Types of Earth Houses
There are three main types of earth houses that the builder can select:
2. Rammed earth.
3. Pressed (or machine-made) blocks.
Two other methods chat can be used are "cob" and "wattle and daub," but usually these do not make the best houses.
ADORE BLOCKS - Walls made from adobe blocks are probably the most popular anti one of the oldest forms of earth housing. Adobe blocks are made by placing a wet mud in boxes called "forms." The forms are removed a short time after the blocks are made anti the adobe blocks are allowed to dry (or cure) for about a month before they are used to build a wall. The blocks are held together in the wall with a "mortar" which can be the same mud used for making the blocks.
The main advantage adobe has over the other methods is that it is the simplest method, and a satisfactory dwelling can be built with the least amount of construction skill. Do it right, and you can have strong walls that are relatively free from cracks. You can also make all of the blocks in your spare time and store them until you are ready to use them.
Adobe has several disadvantages. Adobe blocks are likely to be "rough looking" and chip easily. Adobe is usually not suited to climates that have more than 25-30 inches of rainfall a year.
Walls made from adobe blocks are usually as attractive or more so than rammed earth but like rammed earth, adobe often requires surfacing for a good appearance., Adobe walls probably require less work than do rammed earth walls. The attractive house shown in Figure I is an adobe house covered with stucco.
RAMMED EARTH - In this method, continuous walls are built by ramming moist soil into position between heavy wooden forms. When a short section of wall is completed the forms are moved upwards or sideways and the process is repeated until the walls are completed. The ramming may be done with either hand or pneumatic tampers, but either way the soil has to be rammed until it becomes dense and extremely firm. Pneumatic tampers require more skill for successful use than do hand tampers.
A well made rammed earth wall is one of the most durable earth walls that can be made. Some have lasted for centuries. Unskilled labor can do the ramming.
Rammed earth has the following disadvantages:
1. It is-not easy to do well.
2. The heavy wooden forms take time, money and some skill to build.
Rammed earth construction requires the most careful selection of the soil type, or the walls will shrink and crack after they dry.
The amount of water used in the soil during the ramming must be carefully controlled to get proper ramming of the soil.
If carefully done, the finished wall may look well without any coating. But, it is common practice to stucco or paint the finished wall to produce a pleasing finish. Bonding of stucco or paint to the wall may present a problem if special surface preparation is not carried out.
MACHINE-MADE OR PRESSED EARTH BLOCKS - Recently, several simple and inexpensive machines have been made for pressing soil into bricks or blocks. These earth blocks have many advantages. They have approximately the strength and durability of rammed earth. Some blocks which have had stabilizers (or chemicals) added to them are nearly as satisfactory as burnt brick, lumber, or certain other building materials. At the same time, walls can be built as easily as adobe block walls. The pressed blocks dry and shrink in the sun before they are laid so that walls essentially crack free, can be built even with soils that shrink a little.
Walls made of pressed blocks have a very pleasing appearance (Figure 3) and it is not necessary to use surface coatings as long as the right soils are used. It nevertheless must be remembered that much hard work is required for handling and mixing the soil and transporting the finished blocks.
The next two methods are not recommended for a house you want to last a long time.
WATTLE AND DAUB - In this method, a vertical frame`` work of posts and poles is first constructed. Then reeds, branches, etc., are woven among the poles to form a base for a mud "plaster" which is applied to both sides of the framework. Another way is to make a double wall of poles and reeds and fill the space between with mud also. Figure 4 shows a wattle and daub house.
Shrinkage cracks often occur in walls of this type, and constant maintenance is likely to be necessary. For sick people, and some elderly people, this method of construction is not practical because a wattle and daub house might need repairs when they can least afford to do it. In many cases this is a disadvantage of the other methods already mentioned.
The method is not very practical in areas where durable species of wood are not available.
COB - In the cob method of construction, stiff mud is molded into balls somewhat larger than a person's head. These balls are then piled up in thick layers to form the wall directly without the use of any kind of forms. The mud must be stiff enough so that it will not have a tendency to slump. If some slumping or spreading does occur, the mud is put back in place with a trowel or else the excess mud is sliced off and placed on top. The wall must be constructed slowly so that each layer has a chance to harden before more mud is stacked on top of it. Workers usually stand or sit astride the walls so that scaffolding is not needed.
The only advantages that cob houses have are that they are easy to build and need very little construction equipment. However, shrinkage cracks can usually be expected and they may be serious.