How to choose clay for producing high-strength clay brick in Zimbabwe

Since the turn of the century, Zimbabwe has faced two major challenges in the construction sector: a housing shortage and the high cost of traditional building materials. With a national housing deficit reaching as high as two million units, the government launched the Zim-Asset program in 2013, aiming to deliver 120,000 housing units by 2018; however, only 16,000 units were actually completed, falling far short of the target. Meanwhile, the price of traditional bricks in Zimbabwe was exorbitantly high—exceeding that of neighboring countries—creating an urgent need for a comprehensive, low-cost, and easy-to-implement housing construction system. In response, Zimbabwe’s Astra Building Centre introduced a highly efficient and convenient clay brick technology.

Clay brick technology not only reduces housing construction costs but also preserves local forest resources. Traditional brick firing has long been widespread; however, it entails high production costs and consumes vast amounts of timber, leading to large-scale deforestation and atmospheric pollution. Consequently, Zimbabwe’s Environmental Management Agency (EMA) has restricted extensive deforestation driven by traditional brick production.

Clay bricks are primarily made from local clay; what is the distribution and quality of clay in Zimbabwe? Next, I will explain how to choose clay for producing high-strength clay bricks in Zimbabwe.

01. First is the granitic kaolinite clay from Zimbabwe

This clay type is the most representative and widespread in Zimbabwe, aligning with the country’s geological structure and covering 46% of its total land area; it is primarily concentrated in the Central Plateau, Mashonaland, Masvingo, and East Mashonaland provinces, as well as the area surrounding Great Zimbabwe. Formed mainly through weathering, the clay developed under hot and humid local climatic conditions, where minerals such as potassium and sodium feldspar in the rock were leached out and—following prolonged chemical reactions—transformed into kaolinite minerals.

This type of clay possesses stable chemical properties and a moderate plasticity index (approximately 12%). Containing iron and aluminum oxide minerals such as hematite and gibbsite, it serves as an ideal raw material for producing red clay brick. The soil features a balanced content of cohesive particles and meets plasticity standards; furthermore, its inert clay minerals have minimal impact on cement hydration, facilitating the production of high-strength bricks. Crucially, this kaolinite-rich soil is widely distributed and abundant in Zimbabwe, allowing for on-site sourcing across nearly half the country. The clay can be excavated and crushed for immediate use—eliminating the need to purchase or transport raw materials—which represents a core advantage of this clay red brick technology.

As early as the period between 1100 and 1450, people in Zimbabwe utilized local clay to construct homes; they mixed granite sand with local clay to hand-mold “Daga” bricks—representing the region’s earliest clay brick technology. In 2026, Astra Building Centre used clay brick making machine-made clay brick to construct a perimeter wall for Mpilo Hospital, as well as projects including resettlement housing, teachers’ quarters, and schools in the Tsholotsho area. Beyond these public projects, a resident in the Domboshawa area built a two-story home using these clay bricks; the structure has withstood the test of a decade and remains in excellent condition, serving as a testament to the high strength and durability of the bricks, as well as the superior quality and suitability of the local clay.

02. Next is the analysis of the local red clay in Zimbabwe

Red clay is a widely distributed and highly characteristic type of clay in Zimbabwe, closely linked to geological rock formations and rainfall patterns. It is primarily found in the Central Plateau, Eastern Highlands, Harare, the vicinity of Great Zimbabwe, and the Mashonaland provinces—regions where annual rainfall ranges from 700 to 900 mm. This red clay is the product of prolonged weathering; under the local hot and rainy tropical climate, minerals within the rock undergo leaching and decomposition, leading to the significant loss of elements such as potassium and sodium, while iron and aluminum oxides accumulate and deposit, imparting the clay’s distinctive and easily recognizable red color.

Local red clays can be categorized based on their characteristics into granite-derived red soil and mafic rock-derived red clay. Granite-derived red clay is sandy in texture, with coarser particles, good drainage, and low cohesiveness. In contrast, mafic rock-derived red clay is clayey, with finer particles and higher plasticity. The chemical composition and physical properties of these red clays make them highly suitable for the production of clay brick; since 2006, the local manufacturer Astra Building Centre has been using this local red soil to produce clay bricks.

In Zimbabwe, there are countless examples of buildings constructed using red clay brick made from local red clay, ranging from the Emganwini demonstration house, Barham Green residences, and teachers’ cottages to the buildings at Lupane State University and the Tsholotsho clinic project currently under construction. These projects encompass a wide variety of building types—including social housing, private homes, schools, and hospitals—demonstrating the maturity of the clay brick construction technology.

Clay brick dimensions are not fixed; thanks to years of research and development by our engineers, we now offer dozens of brick types. These range from the classic 230×220×115mm brick to large two-hole bricks (300×150×100mm), U-shaped bricks, CLC bricks, half-bricks, and clay brick pavers. We can also customize dimensions to meet specific client requirements, resulting in a highly diverse product lineup. Moreover, a single clay brick machine can produce this wide variety of clay brick size simply by changing the molds.

03. The third material we are analyzing is the Karoo kaolinite clay from Zimbabwe

Karu kaolinitic clays are primarily distributed across the Mid-Zambezi Basin in Zimbabwe; in the northwestern part of the basin, the clay is predominantly kaolinite, whereas in the southwestern part, kaolinite coexists with chlorite and montmorillonite. These clays originated from freshwater sedimentation rather than the more common processes of leaching and weathering—a conclusion further supported by the distinct vertical and spatial variations observed in the distribution of the kaolinite.

Karoo kaolinitic clay is predominantly composed of kaolinite and is chemically stable and inert, meaning it has minimal impact on the cement hydration process. It possesses a moderate plasticity index of approximately 21%, with a combined content of clay-sized particles and sand ranging from 10% to 40%. Overall, therefore, Karoo kaolinitic clay aligns well with the raw material requirements for clay brick.

Despite the ideal composition of Karoo-age kaolinitic clays, there are regional variations; clays in the northwestern part of the Mid-Zambezi Basin are predominantly kaolinitic and suitable for claymex brick production, whereas those in the southwestern part exhibit excessive plasticity and require the addition of a small amount of sand for modification. Producing high-strength, durable clay brick necessitates scientific testing, optimal raw material proportions, and professional manufacturing and curing techniques.

04. The fourth subject we will analyze is the sodic clay of the Zambezi Valley in Zimbabwe

The sodic clays of the Zambezi Valley possess unique properties and represent a clay type of significant engineering importance in Zimbabwe. Rich in sodium ions, these clays exhibit physical characteristics such as low permeability and high expansiveness. They are alkaline, with pH values ​​ranging from 7.5 to 10.0—a result of the hydrolysis of sodium ions within the clay producing sodium hydroxide. The region features flat terrain where, particularly during the rainy season, rivers and lakes overflow; salts washed down from higher elevations accumulate on the mid- and lower-slope sections of the valley, eventually forming these distinctive sodic clays over long periods.

The sodic clays found in the Zambezi Valley disperse and swell upon contact with water, creating a risk of cracking in clay brick; consequently, this clay cannot be used directly for brick production and requires modification. One method involves mixing 30% sand into the clay, which effectively reduces its plasticity index. A second method is the addition of gypsum; gypsum contains abundant calcium ions capable of displacing the sodium ions present in the clay. A third method involves adding lime, which functions similarly to gypsum by using calcium ions to displace the sodium ions. We recommend that local building material manufacturers conduct detailed testing of the local clay and carry out small-scale production trials before commencing full-scale brick manufacturing; this ensures the feasibility of the modification strategy and guarantees the high quality and durability of the resulting claymex brick.

05. The fifth subject we will analyze is the soil derived from the ultramafic rocks of Zimbabwe’s Great Dyke.

Ultramafic rock clays of the Great Dyke represent a unique soil type in Zimbabwe, distributed primarily in linear, band-like patterns along the ridges and slopes of the Mpinga and Bannockburn sections. These clays are the products of the physical and chemical weathering of magnesium- and iron-rich parent rock. Initially, physical fragmentation of the ultramafic rock yields sand and silt particles rich in iron oxides; subsequent chemical weathering and precipitation processes then give rise to these distinctive ultramafic clays.

Due to its high montmorillonite content, this clay exhibits a high plasticity index; furthermore, the presence of significant amounts of magnesium and nickel interferes with cement hydration and compromises the quality of the resulting clay brick. Consequently, if local builders wish to use this clay for southern clay brick production, they must incorporate substantial quantities of sand to reduce plasticity and lime to adjust the pH level. Compared to high-quality clays such as kaolinite-rich clay or red clay, this ultramafic-derived clay entails higher modification costs; therefore, precise cost calculations are required to determine the production cost per pacific clay brick.

Zimbabwe possesses abundant high-quality clay resources—such as kaolinite and laterite clays—giving clay brick technology a distinct resource advantage in the country. Currently, this technology is rapidly gaining ground in Zimbabwe, with successful applications spanning residential housing, public facilities (including hospitals, dormitories, and resettlement housing), and mining company accommodation. Beyond saving resources and costs, these projects create local employment opportunities; for instance, the 2017 Knowstics Academy boys’ school project saw local workers use clay bricks to construct academic buildings, dormitories, laboratories, and a library, generating over 200 jobs for the community.

In August 2026, the Zimbabwean government announced plans to revise traditional building regulations and establish green building standards, thereby paving the way for the development and formal standardization of clay brick construction materials. The government has explicitly endorsed the use of innovative clay brick minecraft construction methods by domestic developers to lower production costs and minimize environmental impact. Currently, alongside Zimbabwe, numerous other African nations—including South Africa, Kenya, Nigeria, and the Democratic Republic of the Congo—are strongly supporting the production and application of clay brick technology.

The key to the future development of clay bricks in Zimbabwe lies in localized production and skills training. By moving away from an over-reliance on imported building materials and cement raw materials—and instead leveraging local resources—the country can train local youth and the workforce in clay brick production and construction techniques. This approach will create new local jobs and establish a comprehensive ecosystem characterized by national standards, systematic production, and local supply. Ultimately, clay brick technology is poised to become a mainstream solution for Zimbabwe in addressing its housing crisis and promoting green building practices.

If you are interested in topics such as the production and curing of clay brick or the mix ratios of clay raw materials, please feel free to email us with your inquiries.

FAQ

01. What kind of clay is the ideal raw material for producing clay brick?

First is the clay type; a balanced ratio of sand to clay particles is required, with an ideal clay content of 10%–35%. The red clays and kaolinite clays—which are the most widespread in Zimbabwe—feature small particle sizes and serve as ideal raw materials for producing clay bricks. Second is the plasticity index; a plasticity index of 7%–10% is optimal for clay brick production. Third is the organic matter content; surface clay contains high levels of organic matter that can interfere with the cement hydration reaction, so subsurface clay is a better choice as a raw material for production.

02. What materials can be used to replace cement in the production of clay brick?

First are industrial by-products such as fly ash and slag. Currently, fly ash is the most well-established substitute for cement; research indicates that a 20% replacement ratio yields the best results, enhancing the compressive strength of clay brick. Slag possesses latent hydraulic properties and can reduce cement consumption by 50%. Next are natural minerals like gypsum and lime; lime improves raw material quality through ion exchange and contributes to the strength of the clay brick price.

03. What policies has the Zimbabwean government introduced to support clay bricks?

The Zimbabwean government is currently reviewing the Model Building Regulations established in 1977 to remove regulatory barriers and pave the way for the promotion of clay bricks for sale. Meanwhile, Paul Mavima, the Minister of National Housing, has announced plans to accelerate the adoption of clay brick, setting a target of 120,000 housing units. Additionally, the government is providing financial support, including a $63 million credit facility, to develop clay brick technology and establish factories for a green claybank brick plant.

04. Does Zimbabwe currently have green building standards for clay brick?

The Green Building Council of Zimbabwe (GBCZ) is currently developing its own green building standards—comprising building energy efficiency codes, green building criteria, and a localized rating system—with the support of the United Nations Environment Programme (UNEP). The GBCZ Chairperson has noted that promoting green buildings constructed with red clay brick could reduce global carbon emissions by 40% and encourage young Zimbabweans to enter the green building market.

05. How effective are clay brick houses at sound and heat insulation?

Because clay brick are made from high-density clay, they provide a “thermal mass” effect, resulting in excellent sound and thermal insulation for homes. Regarding sound insulation, houses built with clay bricks meet the standards of the South African National Building Regulations (SANBR); they offer a noise reduction rating of 40 decibels, effectively blocking out 60 decibels of external noise. In terms of thermal insulation, clay bricks perform three times better than concrete bricks, boasting a thermal conductivity of 0.354 W/m·K.

06. How many stories can a house built with clay bricks have?

Clay brick have a strength exceeding 7 MPa; those with a width of 220 mm are suitable for use in load-bearing walls for buildings of three stories or fewer. For buildings exceeding three stories, the role of clay bricks shifts from that of a primary load-bearing element to that of an infill material. In multi-story buildings, ring beams and structural columns must be incorporated to enhance the structural integrity of the building.

07. What routine maintenance is required for houses built with clay bricks?

Since clay brick are made by pressing a mixture of clay and cement, waterproofing is the key aspect of the house’s routine maintenance. First, the waterproof coating on the exterior walls should undergo a comprehensive annual inspection; any damage found must be repaired promptly. Second, the drainage system surrounding the house requires maintenance; especially during the season of falling leaves, accumulated foliage must be cleared from gutters to ensure unobstructed drainage. Third, the roof should be inspected annually for damage or leaks, with any issues repaired immediately upon discovery.