The technology of manually molded blocks for building projects

Some call it blocks while others call it 'sandcrete', this is an important building material which we get by mixing powdered cement, sharp sand and water in a ratio made to suit the job it was produced for. You might wonder why I used the phrase 'in a ratio made to suit the job it was produced for'? Okay,  there are many uses for blocks apart from using it to raise the walls in homes and fences. Blocks could be used for a variety of works, including

1. Walling of a house
2. Making a fence wall
3. Building a generator house or any other structure that will have vibrating equipment inside
4. Effluent waste pits or soak away tanks.

Because of the various uses for blocks, the mixing ratio cannot be the same, we tend to reduce the ratio of sand to a bag of cement if we want a more solid mix or a block product which can do more than covering the walls of a house. I will like to mention here that most houses, especially those built with reinforced concrete columns and metal rods, blocks don't bear much loads, this is why you see houses built without blocks at first, the builder will first raise the columns and deck the first floor, then continue with another set of columns which will bear the next floor, and up and up we go.

There are many different types of blocks in modern building, these include;

1. 9" hollow blocks
2. 6" hollow blocks
3. 6" solid blocks
4. 5" solid blocks
5. The fancy blocks for decorative use

These blocks could be used according to the specifications of the building plan you are using. Most houses with more than one floors uses the 9" blocks on the ground floor and maybe the next few floors, but as a house rises in height, it is recommended that the weight of the blocks on the top floors be reduced, ie. If you use 9" blocks to do a ground floor and the next few floor, use 6" to do the topmost floor to ease the weight on the columns, beams and foundation.

There are two major ways of producing blocks, the first is the older method of using manual labour. Skilled block makers using a metal contraption called a mold, they use this mold to compress mixed cement/sand/water to form blocks and leave them on the ground to set.
The second method was a product of industialization and the need for increased output to meet builders demand. A machine was invented to help compress mixed sand and produce blocks. This is the type we call the machine made blocks. This machine uses vibration method to compess blocks as against the manual method. So we will call this second method the vibrated blocks method.

Which one is stronger? Well, it still depends on the mixing ratio, because it is what you mix that the machine will vibrate. I have seen many breakages among machine vibrated blocks as well with hand made blocks. (I will treat this in a new topic)

Apart from bad mixing ratios, which happens when some block makers add too much sand to the mix ratio to get more yield of blocks, some other things can cause blocks to come out in a bad condition which can affect the quality of the project. These other conditions include;

1. Using bad/expired cement

Due to the prevailing economic conditions, some block makers tend to go for very cheap cement which may not have the required quality to hold a solid block. These blocks break soon after they are made. Some cement sellers who hoard cement keep the cement for so long that the quality of the cement is compromised, by this I mean that the cement will lack some of the quality needed to make blocks as the binding agent present in cement may have become weaker. Another thing to note with cement is that some cement sellers rebag cement, removing and reducing the original quantity of cement from the factory. As a consequence the ratio you thought you are using to produce a given quantity is no longer complete, making for a low quality block that can easily break before it is used for the project.

2. Quality of the sand

Some sands are coarse while some are soft. The sharp sand (coarse) is recommended for block making but it should not be too sharp, or it will not be very good for the quality of block. Some people pack dirty sand from the roadside, gutters and ponds. We recommend sharp sands packed from flowing water, or better still the beach. Care should be taken so the bigger pebbles and stones that mix with the sand are filtered out.

3. Rain

Make sure the weather is clear before you start making your blocks, this is because a freshly made block is softer than eggs, and when it rains, the whole blocks can melt and become formless. We have a way to protect the effects of rain if we must make blocks in the rainy season. We buy nylon sheets and use them to cover the freshly made blocks. Also ensure that there are no small erosion tracks passing from under the freshly made blocks.

4. Other domestic animals

Now, keep those your fowls, dogs and goats indoors while making blocks. A running fowl can break more that 10 blocks if it climbs on frshly made blocks, how much more the heavier mammals like goats, sheep, dogs and even cattle. I have seen freshly made blocks trampled upon by animals, and it leads to loss of time and resources.

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