The Home Builder's Manual of Mud Brick Design and Construction, Brickmaking


Author: Alistair Knox

The methods of moulding the building blocks varies from forming them in individual moulds employing a wide variety of pressing machines. such as Singa Rams, to the use of big mobile tumblers that can mix tons of soil and water into a properly pugged mixture which is then placed in multiple grid moulds and left to dry in the landscape. There are still other systems that press the material which has been wetted to a minimum degree so that the block may be lifted and stacked immediately after being formed.

The use of many machine methods implies a cost beyond the scope of the individual home builder. In addition, the mechanically pressed brick often suffers from being improperly wet through or pugged and is held together by a heavy pressure rather than by the ageless method of allowing the thoroughly water percolated earth to fuse the material into blocks of consistent strength and endurance. It is found that mechanically made bricks may start to deteriorate a year or so after manufacture because of dry fragments remaining in the inadequately mixed soil. Good material is ready when it develops a whipped cream consistency. So that When placed in the mould it merely has to be tapped lightly With the sole of the foot before removing the mould. It is not even imperative to strike off the top of the brick with a spade, provided the foot tapping process can completely fill the mould and leave the corners square and full.

It is a mistake to believe that mud bricks must be mostly clay. I have always found the best results occur Where the minimum clay content - consistent with the proper binding of earth that colloidal material provides is used. Most bricks require some straw to be added. The more clay in the mix, the more straw required because straw acts as a form of binding agent. It should be chopped with a hatchet into pieces from 6" to 8" long to prevent the mix becoming difficult to turn over when it is wet.

I have seen almost every conceivable type of soil used and they all seem to work to a lesser or greater degree. The art of making bricks efficiently is of course to evaluate the simplest and easiest method for the individual site. This often requires the mixing of different soils but the result depends, where the bricks are hand-made, in a simple time and motion study of arriving at the shortest way from the dry earth on the land to the properly pugged mixture being deposited in the mould. Where a hand shovel is employed, it becomes inefficient every time wet earth is required to be lifted more than a foot above the ground.

Some natural soils are so benign that they do not require any straw to assist the binding at all. Bricks that are preponderately clay shrink considerably as they dry from the outside in. This uneven process can cause them either to fail altogether or for the cracks to close up as the centre of the brick eventually dries out and shrinks to the same degree but it still weakens the final result. Good soil mixtures will dry without anything beyond hairline cracks, except in very hot condition where the evaporatory process become too fast. In such circumstances it is a good policy to spread wet heshian over them to increase the drying time.

It is also advisable to consider carefully the ground on which the bricks are to be formed. The ideal site is one that is very slightly sloping down preferably from south to north. Making them on the concrete slab or on sheets of polythene is not as good as it sounds because the water takes too long to dry out at the bottom of the brick. Short grass will prove an ideal laying base because it allows the water to filter away and at the same time prevents the moist brick adhering to the earth. It is preferable to make bricks at a sufficient distance from trees to prevent concentrated dripping from the leaves falling on them from a height. It can cause more damage than leaving them in the open. It is remarkable how long newly formed bricks will stand under reasonable rainfall. provided they are made of well mixed and of reasonably stable material.

It is, nevertheless, a truism that no mud brick maker likes the rain, yet in and around Melbourne whose inclement weather is a joke to the rest of mainland Australia, it is truly wonderful how few bricks are lost through water damage. It is possible to make them during the winter but it is highly undesirable because they can take so long to dry. They can even dry to a point just below building strength and then become quite soft if some more rain catches them.

Dull weather seriously slows down the drying in Spring, Autumn and Winter, Where the atmosphere is often moist and still but strong winds at any time make for good quick consistent drying. Once persevered with, it will be discovered that slowly cured bricks will eventually become stronger and better than those that dry fast.

Every attempt should strive to make the process as direct as possible by using some mechanical assistance such as a rotary hoe to stir up the mix. Simple hand-driven cultivators are cheap and easy to hire and any small financial outlay will be reimbursed several times over both in time and the saving of back breaking work.

Now that every Local Council in Victoria is required to give serious consideration to the approval of sensible plans for earth wall buildings they may ask for tests to measure the crushing strength of the dried bricks. Mud brick builders should willingly comply with this requirement because it is cheap to do through a simple test that can be provided by Universities, Technical Colleges and other such institutions. It also provides builders with information that can assist their designs and turn their confidence into certainty. When I first had to specify a minimum crushing strength I nominated 140 lbs to the square inch as being adequate to carry the live and dead load of any normal structure, not excluding heavy roofing materials such as tiles or slates for single storied building. Load bearing walls of two storied buildings should employ 13" thick walls for the first 9'. When the change was made to metric measureaents this was altered to 1 megapascal to the square inch. A megapascal is equal to approximately 143 lbs. This figure was not chance or guesswork, but was based on fifteen years practical experience. If a municipal authority were to prove difficult, a Civil Engineer could use the code governing structures and prove that such walls would hold some five times or more the designed load and would cover any demands that authorities could demand of them. If there is a benighted Municipal Engineer or building Surveyor still surviving in these more enlightened times who still resists, the matter can be settled by going to the building Committee, a body of specialists employed to interpret anomalies and variations to the Victorian building Code. They have always approved our submissions in the past and the sudden explosion in earth building through the entire state has, I believe, dissolved official resistance forever. I know of several building Surveyors who are building mud brick houses for themselves. At a recent Seminar I held I discovered the most enlightened and creative Municipal Engineer I have ever heard of who went much further than I had in his freedom of approach to mud brick structures. In a final word it may be stated that the prejudice and ignorance that once frightened intending builders in Victoria is no longer a threat.

In New South Wales. South Australia and Queensland there are still pockets of resistance but these are quickly being overcome. I recently heard about a case in the Mittagong (N.S.W.) area where a lady applying for a permit was so intimidated by the hard time the authorities promised they would give her that she gave up the whole idea. They said they would leave her alone if she built out in the bush. Had I designed the building for her I could have obtained a permit because they were exceeding their authority. building Surveyors only have the right to administer laws and regulations concerning the stability and sanitation of building projects. They have no jurisdiction over matters of quality of design and choice of materials except in some isolated instances. They at no time are the arbiters of taste and aesthetics.

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