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Producing ISSBs

Table of Contents

Acknowledgements ................................................................................... 2 Course Team .............................................................................................. 2 Table of Contents ...................................................................................... 3 Production of Interlocking Stabilised Soil Blocks ...................................... 4 Introduction ............................................................................................... 4 Module Outcomes ..................................................................................... 4 Module Content ........................................................................................ 5 Topic 1 ....................................................................................................... 5 Introduction to Interlocking Stabilised Soil Blocks ............................................ 5 Advantages of ISSB .................................................................................... 6 Limitations of ISSBs.................................................................................... 7 Topic 2 ......................................................................................................... 8 Tools and Equipment used in ISSB Production ......................................... 8

Equipment used in SSB Production ....................................................... 8 Topic 3 ....................................................................................................... 12 What is Soil? ............................................................................................ 12

Types of Soil ......................................................................................... 13 Topic 4 ....................................................................................................... 15

Soil Testing ........................................................................................... 15 The Bottle or Sedimentation Test ....................................................... 15 The Shrinkage Test .............................................................................. 16

Topic 5 ....................................................................................................... 18 Production of ISSB ............................................................................... 18 Common Problems Encountered During Block Making ...................... 25

Topic 6 ....................................................................................................... 26 Basic Building Guidelines ..................................................................... 26 Foundations ......................................................................................... 26 Cement/Sand mortars ......................................................................... 26 Corners and Openings ......................................................................... 26 Roof Overhangs ................................................................................... 27 What have we learnt? ......................................................................... 28

Answers to Activities ............................................................................... 30 Glossary ................................................................................................... 32 References ............................................................................................... 32

Producing ISSBs

Producing Interlocking Stabilised Soil Blocks

Introduction Welcome to this course on brick making. In this module you will learn how to produce interlocking stabilised soil blocks (ISSB). As you well know, soil is one of the main materials used for the construction of traditional low-cost houses in rural areas. This is because it is cheap and locally available. Some houses are constructed entirely or partially with soil, depending on the local traditions, climate, available skills and cost. One disadvantage of traditional soil-based construction is that they require regular maintenance and protection. This has led to the development of new methods or technologies that improve the quality and durability of soil construction methods. One such method is brick making. There are two basic types of bricks used for construction, namely:

• fired bricks which are compressed and baked in a type of oven known as a kiln;

• unfired bricks which are compressed and laid out in the sun to cure. There are many types of unfired bricks. However, in this course we shall discuss the type known as interlocking stabilised soil blocks. These are stabilised soil blocks made of moistened soil mixed with a little cement. The blocks are then compressed either manually or mechanically and cured. You will learn about the tools and equipment used to make the soil blocks and how to select and test the soil used for making them. In addition, we shall examine how to produce blocks and use them for construction. Let us start by reviewing the module outcomes.

Module Outcomes On completion of this module you should be able to:

• discuss the advantages and limitations of using ISSB; • list the tools and equipment used in the production of ISSB; • select suitable soil for the production of ISSB; • conduct soil tests to establish whether it is suitable for block making • describe the steps used in the production of ISSB; • describe the areas that require special attention when building with ISSB.

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Producing ISSBs

XmmYmm x 100 = % of clay in the soil.

Topic 4

Soil Testing Before any block making commences, you need to analyse the properties of the soil to determine its suitability and the amount of stabilizer that needs to added. There are two basic field tests which must be carried out on every soil. These are: • The bottle or sedimentation test • The shrinkage test

The Bottle or Sedimentation Test The aim of this test is to help determine the approximate amount of clay, silt, sand and gravel in a soil sample. With many soils, it is very difficult to differentiate between silt and clay, however it is easier to determine the percentage of sand or clay. Testing Procedure: 1. Start by sieving the soil to be tested with a 6mm sieve 2. Find a clear bottle with a flat bottom and reasonably straight sides 3. Fill it quarter full with soil 4. Add clean water until you completely cover the soil 5. Add a pinch of salt to the bottle contents. The salt helps to accelerate the

settling and segregation of particles. 6. Firmly close the lid of the bottle and shake until the soil and water are well

mixed - about 1 minute. 7. Allow the bottle to stand on a flat surface for about 30 minutes so that the

contents can settle. 8. The heaviest particles, that is gravel, will settle at the bottom followed by

sand, silt and clay. 9. To work out the percentage of clay in the soil, you should use the following

procedure: - Measure the total height of soil from the bottom of the bottle to

the top of the soil and record it as X mm. - By looking closely at the soil layers, you will be able to determine

where the clay content starts. Measure the height of the clay and record as Y mm.

- To work out the percentage of clay in the soil, use the formula described below:

The SThis testhe soi

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7

Producing ISSBs

Figure 7: Sieving the soil with a wire mesh screen.

Topic 5

Production of ISSB As we have mentioned before, the basic materials required for production of ISSB are soil, stabiliser (cement) and water. The following are the steps to follow in production of interlocking stabilised soil blocks. 1. Dig or excavate the soil:

• Tools: You will need to have a hoe and a spade. • Method: With the use of a hoe excavate or dig out the identified soil

and crush the big lumps by hitting them with the back of the spade. 2. Sieve the soil:

• Tools: 6mm sieve and a spade • Method: The simplest sieving device is a screen made from 6mm wire

mesh, and nailed to a supporting wooden frame and inclined at 45 degrees to the ground. See Figure 5 below. Using a spade, you should throw the soil against the screen. The fine material will pass through while the course oversized material will ran down the front.

Once you conduct a soil test and estimate the amount of cement you will need, the next step is to start making the stabilised soil blocks. Let us learn how that is done in the next topic.

Producing ISSBs

Figure 8: Filling the mould with soil/cement mixture.

Note that the particles which are retained on the sieve can be further crushed and sieved again. 3. Batching and Mixing

• Tools: Shovels; Bucket; Watering can • Method: Once you establish the right proportions, identify a

measuring device, such as bucket, for your materials. o Using the bucket, measure or batch out the soil and cement

required for a particular production. o Using the shovels, mix the dry cement and soil three times

until the mixture has one uniform colour. o With the use of the watering can, add water gradually to the

mixture of soil and cement until it is moist but not too wet. When you squeeze a handful of the soil mixture in your hand, no water should ran between your fingers.

4. Loading the Press

• Tools: You will require the following equipment and tools; Soil press machine; Shovels; Brush.

• Method: Open the press cover of the brick making machine. o Check the piston cover to ensure that it is sitting on the

adjusting knob. o Using a brush, apply oil inside the mould. This is only done at

the start when the blocks tend to stick. o Fill the mould box flush on top with the soil/cement mix as

shown in figure 7 below. o Drop the mould cover gently to cover the mould box. In so

doing, the soil inside is pre-compacted.

Producing ISSBs

Figure 9: Block compacting machine.

Figure 10: Worker bringing down the handle of a compacting machine.

5. Compacting the Block

At least two people are required for this operation. • Method: Open the lever latch as the person on the other side takes

over the handle to compact the block.

• The handle is brought down by the person compacting the block until the lever arms touches the compaction stop.

• This indicates that maximum compaction has been achieved.

Producing ISSBs

Figure 11: Removing the block from the machine.

6. Ejecting the Block

Once the block has been compressed, the next step is to eject the block. • Method:

o Pass the handle to the person on the opposite side of the press to start the ejection stroke.

o Ensure that the lever latch is locked in position, while the handle is moved from the vertical position so that the cover can be opened.

o Bring the handle all the way down as the block is being ejected.

o Remove the block gently by holding it along the sides and take it to a well-sheltered area for curing as illustrated in Figure 10 below.

o To make more blocks, repeat the same process again. 6. Curing The last process in block making is curing. This starts the following day after production when the blocks are approximately 24 hours old. Curing is the process of controlling the setting or hardening of the soil block, so that it can gain maximum strength. This is a common requirement for materials with cement. If a product with cement dries very fast in the sun, it loses all the strength and start disintegrating. To acquire maximum strength, any cement product with cement must be laid out to dry slowly in wet or humid conditions for a few days. This is what is referred to as curing. If curing is not done properly, the surface material will lose its moisture and the clay particles will shrink. This will cause surface cracks on the block faces. The final blocks will be of poor quality and all the time and money spent in producing the blocks will have been wasted.

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Producing ISSBs

Next let us discuss the common problems one is bound to encounter during block making and their solutions.

Common Problems Encountered During Block Making While producing bocks, you might encounter some minor problems, which you might not know of their immediate cause. The Table 1 below summarizes some of the possible problems with the machine and the solutions.

NO PROBLEM SOLUTION

1 Compaction of blocks is too hard

• Check if you are loading too much soil in the press. Adjust the volume of your moulding box using the adjusting knob

• The other possible cause for this problem is if the mixture is too dry. Check your water content

2 Compaction of blocks is too easy

• You are probably not putting enough soil in the moulding box. Adjust the volume of your mould box.

• Your mixture might have excessive water. Check your water content

3 The blocks have broken edges when ejected

• Oil the mould box. • Check whether your mixture is too wet • Check whether your soil might be

containing too much clay.

4 Block disintegrates while testing.

• Check whether the curing procedures was strictly followed.

• Check whether the soil is sieved before production

That brings you to the end of this topic on block production. We hope that you are now well informed about how blocks are made. In the next section we shall look at basic building guidelines when using ISSBs.

Producing ISSBs

Topic 6

Basic Building Guidelines When building a house with ISSBs, you should take special care in the following areas:

• The foundation • Cement/sand mortar to be used • Corners and around openings • Roof overhangs

This is because the foundations, corners and openings are the areas which are most vulnerable to water damage and erosion. Let us look at the guidelines for each starting with the foundations.

Foundations When building the foundation walls, you should use quarry stones or concrete blocks. If you must use ISSB’s then it is recommended that you use special blocks which are made with twice the amount cement used on the basic blocks used for the super structures.

Cement/Sand mortars When laying the blocks, you should not use cement or sand mortar that is stronger than the blocks themselves. This can cause the mortar to crack thus exposing the block to rain. The mortar strength should be slightly weaker or equal strength to the blocks. Mud mortars can also be used and later on raked externally to make the joints waterproof. Generally, the bed and vertical joints should not be bigger than 12mm.

Corners and Openings Since the corners and openings are more vulnerable to erosion, it is recommended that all corners and the areas around openings should be plastered, see Figure 15. This applies also to the base of the building which must be plastered at least 300mm above the ground level. Again, you should make sure that the cement/sand is not stronger than the blocks themselves. Otherwise the plaster may crack.

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Producing ISSBs

Congratulations! You have now come to the end of this course. We hope you have found it interesting and informative and that you now have the necessary knowledge to make interlocking stabilised soil blocks. To check if you have mastered the content of this course, go back to the outcomes at the beginning of this course and check if you have achieved them. If you have, take time to practice what you have learnt because practice makes perfect! Good luck!

Producing ISSBs

Answers to Activities

Answer to Activity 3 (1) What is the difference between a manually operated and a motorised

interlocking stabilised soil block making machine The motorised machine uses diesel or electricity to run while the manual ones does not. The manual machine produces one block at a time while some motorised machines can produce 2 or more blocks at a time.

(2) List the tools that are used for making interlocking stabilised soil blocks.

1. Bucket; 2. Oil can; 3. Watering can; 4. Sieve; 5. Shovels; 6. Trowels; 7.Hoe; 8. Pan; 9. Rammer; 10. Broom.

Answer to Activity 6: Soil Tests What is the difference between the bottle test and the shrinkage test?

The bottle test assesses the quality of the soil in terms of the proportions of each particle. While the shrinkage test is performed to help you calculate the amount of cement that should be added to the soil.

Activity 7: Process of Block Production Arrange the following steps of block making in the right order:

1. Dig or excavate the soil: 2. Sieve the soil: 3. Batching and Mixing 4. Loading the Press 5. Compacting the Block 6. Ejecting the Block 7. Curing 8. Stacking the Blocks 9. Testing The Blocks

Producing ISSBs

Activity 8: Building guidelines for ISSBs List the four areas that require special attention when building with ISSBs in Column A and write the reasons why care is needed in Column B.

Column A Column B

1. Foundation

Foundations are vulnerable to water damage and so require quarry stones or concrete blocks or ISSBs with twice the amount of cement used in ordinary blocks

2. Use of cement/sand mortars Cement or sand mortar should not be stronger than the block to avoid cracking

3. Corners and openings Should be plastered to protect from erosion

4.Roof overhangs To provide protection to the walls

Producing ISSBs

Glossary Compress To squeeze the soil mixture with a machine

Stabiliser Material added to soil to make it stronger and water proof, such as cement or lime.

Interlock To fit or join two blocks closely together

Mortar A paste made up of cement and sand used to bind blocks together

Compacting To exert force on a soil mixture in order to compress it

Mould A container used to give shape to something

Lubricating To oil something

Decayed To rot or decompose

Batching The process of measuring and combining ingredients for block making.

Curing Keeping blocks moist so that they can achieve maximum strength.

References 1. UN Habitat (2009). Interlocking Stabilised Soil Blocks: Appropriate Earth

Technologies in Uganda. UN Habitat/Adrian Perez. 2. UNESCO (2001). Compressed Stabilised Earth Block Manufacture in Sudan.

UNESCO, Paris. 3. Weinhuber, K. (1995) Building with interlocking blocks. German

Appropriate Technology Exchange, GTZ (GATE), Eschborn. 4. Teach a Man to Fish, Income Generating Activity Information Sheet,

Stabilised Soil Brick (SSB) Brick Making

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