Why experts are against the use of burnt building bricks

Women labor at brick making site in Sironga village, Nyamira county loaded with bricks transport them to display area by the main Nyamira-Kisii road on November 24,2020. Women have embraced hard work in the area to bring food on the table and to sustain family needs as most men have lost their jobs during Covid-19 and unable to provide for their families. [FILE/Standard] Experts are advising against using burnt bricks for construction and instead pushing for using more environmentally friendly alternatives, such as cement blocks and stabilised soil blocks. Burnt bricks, according to a guide prepared by Financial Sector Deepening (FSD) Kenya, consume a lot of water, and their production process results in losses. Stabilised soil blocks and sand-cement blocks, on the other hand, use less water to produce and also do not involve the cutting down of trees. The FSD Kenya guide titled Creating Climate-Smart Rural Affordable Housing targets developers and homeowners. It has been developed in partnership with K-Rep Fedha Services Ltd, an organisation that offers oversight to financial services associations at the grassroots level. The May 2025 guide states that while there exist different technologies to erect walls, stabilised soil blocks and sand cement blocks are superior to burnt bricks due to their climate-resilient properties. It explains that burnt bricks, being made from agricultural soil, destroy the environment. This is considering that it requires a minimum of five trees to burn 16m2 of bricks. A significant number of the bricks are also lost during production, FSD says. "Burnt bricks are the most used material for building modern and permanent buildings in Ukambani - Makueni, Kitui and Machakos counties of Eastern Kenya. This technology destroys the environment through the cutting of trees used to burn the bricks and agricultural soils used to make the bricks," FSD says in the guide. It adds that burnt bricks also consume a lot of water, and 40-50 per cent of the bricks are lost in the course of the production process through breakages. "There is, therefore, a need for alternative walling materials that are environmentally friendly and climate-resilient technologies. SSB (stabilised soil blocks) and SCB (sand cement blocks) are such alternatives, which are not only climate resilient but also cheaper than burnt bricks," says FSD in the guide. For stabilised soil blocks, FSD argues that there is zero wastage as they are machine-made. They are made up of six to 10 per cent cement, with a 16m2 house requiring only 15 bags of cement. Additionally, they are produced on site using soil dug from the foundation. Sand cement blocks, on the other hand, are also made from local sand, comprising 12 per cent cement. "Requires only a simple hand mould that can be moved from site to site. It also requires basic skills to produce quality blocks," the guide reads. Cement in stabilised soil blocks is used as a stabiliser and also to improve its water resistance properties. "Stabilised is a better and cheaper alternative to burning bricks, as it conserves trees and saves on carbon emissions," the guide says, adding that there is no waste during construction, as the soil dug from a pit latrine or foundation is viable for construction. "A manual block compressing machine is used to compress the SSBs, resulting in a solid, dense and water-resistant building block. One bag of cement produces, on average, 90 blocks (290x140x120mm), equivalent to four square metres of walling." Similarly, for sand cement blocks, the cement component is also used as a stabilising and binding agent. "One bag of cement, on average, produces 25 blocks (390x200x150mm), equivalent to two square metres of walling," the guide explains. The portability of the hand mould that can be moved from one site to another is one of the advantages of sand cement blocks being touted in the guide as a versatile technology. "The key to quality production of sand cement blocks is in the thorough mixing of cement and sand and the wet curing of the blocks for a minimum period of 21 days," the guide says. The document states that sand cement blocks should be made using clean coarse or rough sand without vegetation or humus waste. The ratio of sand to cement is 7:1. "Add a measured quantity of water, half the amount of cement used. If you have used one bucket of cement, add only half a bucket of water. Make also mixes you can use within 30 minutes," reads the guide, which also offers a step-by-step procedure on how to make the blocks. Direct sunlight The moulds in use should be clean, and the blocks should be made under a shade, protected from direct sunlight, wind and sun. They are then covered with a polythene sheet and left to dry. The blocks are then watered on the third day before being covered once again, airtight, for 18 days. After this process, their quality is tested by dropping them from a height of one metre. "Good blocks should not break. If they break, do not see or build with them," the guide says. For stabilised soil blocks, the guide states that they are not only better than burnt bricks, as no firing (baking) is required but also help with finishing of the house. "They use very little cement for laying blocks or plastering as they are of uniform shape," the guide says. The process of making stabilised soil blocks is however a bit complicated when compared to sand cement blocks. The soil needs to be sieved to break the big lumps. "If for instance you are using a ratio of 1:14( one bucket cement to 14 buckets soil, measure out the 14 buckets of soil first then add the one bucket of cement on top of the soil," the guide reads. This is then mixed until it gets a uniform colour and water added in small quantities. The mix should be firm but not form mud. A minimum of four people are required to operate the blocks making machine: one to fill the mould, second to compress the block, third to eject the block and fourth to remove the block and placing it on a flat surface protected from direct sunlight. "The blocks should dry under cover for the first 24 hours, after which wet curing should start by watering the blocks with a watering can," the guide says. On the third day, they should be firm enough to be stacked at a height of one metre, watered and covered with polythene for the next 18 days. Later, the polythene sheet can be removed and a drop test conducted at a height of one metre for strength. "A good block should not break but remain as one piece," the guide says. A water absorption test is also conducted after the 28 days. A randomly selected block is immersed in a bucket of water for 24 hours. "A good block will remain rigid and will not wear out or dissolve in the water," the guide reads.

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