Use interlocking blocks to reduce construction costs

In Kyasira Village, in Katabi Town Council Wakiso District, is a modern. It looks so simple and so elegantly suited to its locale. The house is a prototype built using the green technology. The shiny and smooth exterior is a clear vanish that gives the house protection from water.

Constructed by Habitat for Humanity Uganda, the house has two bedrooms, a kitchen, living room and bathroom, with a shower and a waterborne toilet. A waterborne toilet was the best choice, for those times when there is no running water because it is easy to flash by pouring water in the toilet. The rooms compared to many fancy city apartments are spacious. The living room has a window extension to have more room for a reading desk.

The roofing material on the house was got from locally sourced eucalyptus trees that were first dried and then vanished with a wood preservative before roofing.

This is one way of encouraging conservation because it encourages one to grow trees if they have a long term construction plan, which saves the costs of buying and transporting timber. The house represents a milestone for the organisation which, has been able to demonstrate to the community the possibility of building a quality house affordably.

According to James Tanga, a construction specialist at Habitat for Humanity Uganda, the house at Garuga cost Shs35m from start to finish.

This is greatly attributed to the use of green technology which uses interlocking stabilised soil blocks instead of steel, concrete and cement that is commonly used on most construction projects.

These blocks, Tanga explains, require very little cement, sand and soil to bond during construction. They do not require burning, in addition to being optional to plaster at finishing stage.

How the blocks are made

Interlocking stabilised soil blocks are made using murrum soil that is normally brown in colour, sand that is similar to that used in plastering and little cement.

The three materials have to be thoroughly mixed well and pressed together in a machine to create a bond that will hold the mixtures together. The murrum has to be sieved to remove the big particles to remain with a fine layer so that it mixes well with cement and sand.

Nicholas Mwesigye, a civil engineer says the cost of murrum soil is in most, if not all cases determined by the size of the truck that transports it to your site. Whereas a Sinotruk costs Shs500,000 within Kampala, smaller trucks such as Isuzu Forward or Elf costs between Shs150,000 to Shs200,000. 

“If you want the best quality murrum, you have to be at the source or have someone trustworthy supervise the transaction. Some dealers tend to compromise the quality by mixing it with other types of soil. It also depends on the purpose for which you need it,” Mwesigye explains.

Mix ratios

According to Tanga, for the foundation blocks, you need approximately 10 percent cement in the mix ratio of sand and soil.

“For the blocks that make up the super structure, from the foundation to the wall plate, you are looking at five to eight percent cement depending on how the murrum and sand soil is. If the foundation starts from the soil and the blocks will be exposed to water from underground, you have to increase the cement content to 10 percent. There is materials known as water proofing cement, a powdery cement that comes in smaller sacks,” says Tanga.

If you want to make blocks for the foundation, for every bag of ordinary cement, you have to mix it with water proofing cement and make sure that it is 10 percent of the quantity mixed. For instance, if you have the equivalent of 10 bags, one bag of water proofing cement should be mixed with the equivalent of the 10. The water proofing cement should be one out of the nine that constitutes marram or soil and sand that’s well sieved. 

“Green technology is when you save on energy or the environment. The machines used for compressing the mixture of sand, cement and marram are echo-friendly and do not use any power, fuel or wood. After making the mix ratio for the blocks you want, you simply press the machine and the blocks will be ready,” Tanga explains.

“When ready, give the blocks time to cure. Curing means you keep it in a moist place for 28 days as you sprinkle water on them to go through the process that makes the cement gain more strength. They will be ready to use after 28 days,” Tanga adds.

By using interlocking stabilised soil blocks as an alternative to clay or concrete bricks, you are saving the environment by not burning trees.

Secondly, they are made at the site, meaning that you will not incur the costs of transporting materials. If you have good soil or marram on your site, as you excavate for a septic tank or a soak pit, the excavated soil is what you use. These are contributions that go towards lowering the cost of the house.

This technology is perfect for areas that have no artificial sources of heating or cooling. Since the walls are made from high compacted bricks, their density enables them to resist the airflow resulting in warm interiors.

On the other hand, interlocking bricks have less density than conventional bricks that allow good air-flow. So, walls with these bricks are much cooler inside. 

Benefits

Interlocking blocks are becoming popular in wall construction. This is because they are locked against each other without the use of cement mortar, they make things easier and foam a stable building structure that reduces the cost and time of the construction process.

As we all know, cement is becoming expensive and sand scarce. These interlocking bricks come in as a great alternative to construction because they are used without the need of cement mortar.

Also unlike the conventional bricks, the blocks do not necessarily require highly skilled labour.  Because of the way they are used, a layman or an unskilled labourer is able to easily grasp the construction procedure, chich reduces labour costs. 

Daniel Kyeyune, a builder argues that like clay bricks, interlocking stabilised soil blocks, when made well to meet the acceptable standards, do not only equally offer quality and strength of walls but they also greatly cut the construction costs on materials.

For example, if you choose not to plaster, vanish is much cheaper compared to paint.

A four litre tin of vanish costs between Shs20,000 to Shs25,000 yet paint and undercoat cost between Shs30,000 to Shs50,000 or more respectively, depending on where you buy it from. Even with a natural appearance, you remain with an aesthetically pleasing look.

Grow your own materials

If you intend to build in five years’ time and you have land, you can plant trees and they will be ready for use, depending on the type of eucalyptus trees you grow. There are varieties that grow fast and ready for use in three years, as well as those that take longer.

Comparison to others on the market

Some aspects such as plumbing and iron sheets are standard across all kinds of houses. However, where you have a great saving on using interlocking blocks is on the wall construction because it is optional to plaster or paint.

“When you use interlocking blocks, you save about 30 percent on the cost of the wall. To make it appealing to the urban population that prefers finer houses, there is an option of being plastered and painted as opposed to using vanish on non-plastered blocks,” Tanga adds.

According to Lceted, an online portal, interlocking blocks are economical. Interlock bricks are made of cement with the addition of cement and sand, so they are made of cement at a lower cost than conventional bricks.

The portal explains that interlocking bricks cost 35 percent less than conventional bricks. Interlock bricks may contain 10 percent cement, with the remaining mixture containing soil and sand.

“Earthquake resistant. The reason is simple. Ordinary bricks rely on mortar for its support system. If the mortar fails, the entire wall or building will fail. But interlocking bricks have their own support system that does not depend on the mortar. They effectively support each other,” the portal states.

Interlocking blocks offer better insulation in hot areas. They are also suitable for hot areas. Because it is compressed, it has more mass and the brick keeps the interior of the building cooler.

Downside

According to Lceted, interlocking blocks are not suitable for high-rise buildings. Interlock bricks are not safe for high-rise buildings. In fact, they are only good for the first three floors of a building. That is why interlocking bricks are usually reserved for residential buildings and are not used to construct commercial buildings.

Conserve

If you intend to build in five years’ time and you have land, you can plant trees and they will be ready for use, depending on the type of eucalyptus trees you grow. There are varieties that grow fast and ready for use in three years, as well as those that take longer.

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