What are the different types of concrete blocks?

The main types are hollow blocks, which contain cavities that reduce weight and can be reinforced with grout, and solid blocks, which are dense units with no significant voids. Hollow blocks are lighter and cheaper, suitable for non-load-bearing walls. Solid blocks are stronger and heavier, ideal for load-bearing and foundation walls.

What is the standard size of a concrete block in Tanzania?

The standard concrete block size in Tanzania is 400mm long by 200mm high, available in thicknesses of 100mm, 150mm, 200mm and 250mm. The 200mm thick block is the most commonly used size for external load-bearing walls in residential and commercial construction.

What strength class of block do I need?

For load-bearing walls in single-storey homes, Class B blocks (5 MPa minimum) are standard. For two-storey buildings and commercial structures, Class A blocks (7 MPa minimum) are recommended. For non-load-bearing partition walls, Class C blocks (3.5 MPa minimum) are sufficient and more economical.

How many blocks do I need per square metre?

For standard 400mm by 200mm blocks with 10mm mortar joints, you need approximately 12.5 blocks per square metre of wall area. This rate applies to both hollow and solid blocks of the same face dimensions. Add 5-10 percent for wastage and cutting.

Where can I buy quality concrete blocks in Tanzania?

Tanzibaba manufactures and supplies quality concrete blocks in all standard sizes and strength classes, with delivery available throughout Dar es Salaam and surrounding regions. Our blocks are produced under controlled conditions with regular quality testing. Contact us for a free quote.

Concrete Blocks Complete Guide

What Are Concrete Blocks?

Concrete blocks, also known as concrete masonry units or CMUs, are prefabricated building materials made from a mixture of Portland cement, aggregates such as sand and crushed stone, water and sometimes additives or admixtures. They are manufactured by pouring the concrete mixture into moulds under vibration and pressure, which creates dense, uniform blocks with precise dimensions and consistent quality. After moulding, the blocks are carefully cured for a minimum of 28 days to allow the cement to fully hydrate and achieve their designed compressive strength. Concrete blocks are the most widely used building material for wall construction in Tanzania, forming the structural backbone of everything from modest residential homes in Dar es Salaam suburbs to multi-storey commercial buildings in the city centre. Their popularity stems from their versatility, durability, cost-effectiveness and the speed with which walls can be constructed using blocks compared to traditional brick or stone masonry. Concrete blocks are available in a range of sizes, strengths and configurations — including hollow and solid types — to suit virtually any construction application. Understanding the characteristics, types and specifications of concrete blocks is essential knowledge for builders, contractors, architects and homeowners planning construction projects in Tanzania.

Hollow Blocks vs Solid Blocks

The two primary categories of concrete blocks are hollow blocks and solid blocks, each offering distinct advantages depending on the construction application. Hollow blocks contain one or more hollow cavities or cores that typically account for 25 to 50 percent of the gross cross-sectional area, reducing the block weight and material content while maintaining adequate structural performance. The cores can also be used for vertical reinforcing steel and grout filling in load-bearing wall systems, combining the light weight benefits with the structural strength of reinforced masonry. Hollow blocks weigh approximately 12 to 17 kilograms each depending on size, making them significantly easier to handle, transport and lay compared to solid blocks. The air cavities within hollow blocks provide thermal insulation properties, helping to keep interior spaces cooler in Tanzania's warm climate. Solid blocks, by contrast, have no significant cavities and are manufactured as dense, solid units weighing 20 to 28 kilograms each. Their greater density provides higher compressive strength, typically 7 to 15 MPa compared to 3 to 7 MPa for standard hollow blocks, making solid blocks the preferred choice for load-bearing walls, foundation walls and retaining walls that must carry significant structural loads. Solid blocks also provide superior sound insulation due to their mass, making them ideal for party walls between adjoining properties and walls along busy roads. The choice between hollow and solid blocks depends on the structural requirements, thermal performance needs, budget considerations and specific application. For non-load-bearing partition walls, infill panels in frame structures and upper storey walls where weight reduction is beneficial, hollow blocks offer the best balance of cost and performance. For load-bearing applications, foundation walls and structures requiring maximum strength and durability, solid blocks are the clear choice.

Concrete Block Sizes and Dimensions

Concrete blocks in Tanzania are manufactured in a range of standard sizes designed for modular construction with consistent mortar joint dimensions. The standard face dimensions for all block types are 400mm long by 200mm high, with the mortar joints adding 10mm to each joint, resulting in a module of 410mm by 210mm per block position. This modular system means that four blocks laid end-to-end with mortar joints measure exactly 1.64 metres, and five courses of blocks measure exactly 1.05 metres, simplifying construction planning and dimensioning. Block thickness, which determines the wall width, varies according to the application. The most commonly used thickness is 200mm, which produces a finished wall width of approximately 210mm including plaster on both faces. This thickness is the standard for external load-bearing walls in residential and commercial construction, providing adequate structural strength, thermal insulation and weather resistance. For internal partition walls where no structural load is carried and floor space is at a premium, 100mm or 150mm blocks are used, producing thinner walls that maximise usable room area. For heavy-duty applications such as basement walls, retaining walls and security perimeters, 250mm blocks provide the additional thickness and mass needed for these demanding conditions. Half-blocks measuring 200mm by 200mm by the same thickness as the wall blocks are essential for finishing wall ends, building corners and filling spaces at openings where a full block cannot fit. Lintel blocks are U-shaped units designed to be placed over door and window openings, with the channel filled with reinforced concrete to create structural lintel beams. Ordering the correct mix of full blocks, half-blocks and lintel blocks is essential for efficient construction and minimising wastage. Tanzibaba manufactures all standard block sizes and special units to precise dimensional tolerances, ensuring consistent wall alignment and smooth construction progress.

Strength Classes and Specifications

Concrete blocks are classified into strength classes based on their minimum compressive strength, which determines their suitability for different structural applications. In Tanzania, the commonly specified strength classes are Class A with a minimum compressive strength of 7 MPa, Class B at 5 MPa minimum, Class C at 3.5 MPa minimum and Class D at 2.8 MPa minimum. Class A blocks are high-strength structural units suitable for load-bearing walls in multi-storey buildings, retaining walls and structures subjected to heavy loads. Class B blocks are the standard specification for general load-bearing construction including single and two-storey residential buildings and light commercial structures. Class C blocks are suitable for non-load-bearing partition walls, infill panels in reinforced concrete frame structures and internal walls that do not carry structural loads. Class D blocks are used for temporary structures, non-structural applications and situations where strength is not a primary concern. The compressive strength of a block is determined by testing a specimen in a compression testing machine following standardised procedures, with tests typically performed at 28 days after manufacture to allow full strength development. Several factors influence the achieved strength of concrete blocks, including the cement content and water-to-cement ratio of the concrete mix, the quality and grading of aggregates used, the manufacturing process including vibration pressure and compaction, and the curing conditions during the critical early strength development period. Blocks produced under controlled factory conditions with consistent mix design, proper vibration and adequate curing achieve more reliable and consistent strength than blocks produced in uncontrolled environments. Tanzibaba manufactures blocks to specified strength classes with regular testing at our laboratory, providing test certificates to confirm that each production batch meets or exceeds the required compressive strength.

Installation Basics for Concrete Block Walls

Proper installation of concrete block walls requires careful preparation, skilled workmanship and attention to detail to produce walls that are straight, plumb, strong and durable. The foundation or base on which the wall is built must be level, true and structurally adequate to support the wall loads. A damp-proof course of bituminous membrane or polyethylene sheet is installed at the base of the wall to prevent moisture rising from the ground into the blockwork through capillary action. Mortar is the binding material that holds blocks together and fills the joints between them. The standard mortar mix for block laying in Tanzania is one part Portland cement to four parts building sand, mixed with clean water to a workable consistency that holds its shape when pressed but can be spread easily with a trowel. Each block is laid on a full bed of mortar on the horizontal joint face, with mortar also applied to the vertical joint face before the next block is pushed into position. The mason uses a spirit level frequently to check that each block is level horizontally, plumb vertically and aligned with the adjacent blocks in the wall. Joint thickness should be consistent at 10mm throughout the wall for a uniform appearance. Vertical reinforcement bars are placed at corners, wall junctions and both sides of openings at positions specified by the structural engineer, with the reinforcement extending down into the foundation and up into the ring beam. A ring beam or bond beam of reinforced concrete is cast at the top of each storey height to tie the walls together, distribute roof and floor loads, and provide lateral stability against wind and seismic forces. The ring beam is typically formed using U-shaped lintel blocks or timber formwork with reinforcing steel placed inside and concrete poured to fill the section. After laying, the mortar joints should be tooled or pointed to compact the mortar and create a weather-resistant finish. Newly laid block walls must be protected from direct sun and rapid drying during the initial curing period to allow the mortar to achieve adequate strength. In Tanzania's hot climate, wetting the walls with water during the first few days after construction helps prevent premature drying and cracking of the mortar joints.

Concrete Blocks Complete Guide — Everything You Need to Know

What Are Concrete Blocks?

Hollow Blocks vs Solid Blocks

Concrete Block Sizes and Dimensions

Strength Classes and Specifications

Installation Basics for Concrete Block Walls

Frequently Asked Questions

What are the different types of concrete blocks?

What is the standard size of a concrete block in Tanzania?

What strength class of block do I need?

How many blocks do I need per square metre?

Where can I buy quality concrete blocks in Tanzania?

Need Concrete For Your Project?

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