Masonry blocks, or concrete masonry units (CMU), are precast blocks used in construction since 1882. They are economical, environmentally friendly, fire-resistant, and durable. Blocks come in two grades and various sizes, types, and shapes. They are made from Portland cement, sand, gravel, and water, with additives for durability and coloring. Manufacturing involves machine molding, polymerization at high temperature, and solidification. Masonry block construction is fast and compatible with conventional masonry supplies. It requires standard mortar joints and can be reinforced with steel or concrete where required. Professional advice and consultation of local building codes are recommended before starting construction.
Masonry blocks, also known as concrete masonry units (CMU), are precast blocks, solid or hollow, used in construction since 1882. They are economical, environmentally friendly and provide excellent structural strength to residential, commercial and and industrial in rural and urban areas. They are also fire resistant, durable and require minimal maintenance.
These blocks come in two grades determined by compressive strength and purpose. CMUs in both grades are load bearing, but differ in the type of concrete wall in which they are used. Grade N blocks are suitable for lower and upper level exterior walls. Grade S blocks, on the other hand, are only used for raised exterior walls with a weatherproof finish, or in walls that are not exposed to the weather.
Size, type and shape, blocks vary widely. The nominal standard size is 8 x 8 x 16 inches (20.32 x 20.32 x 40.64 cm). The different types of blocks are plain, ash or breeze, clinker and aerated concrete. They come in block shapes such as stretcher, split-face, sill, lintel, edge, corner, screen, cinder block, and shade.
The basic materials used in the production of regular high density masonry blocks are Portland cement, sand, gravel and water. This mixture is modified in the case of cinder blocks and low density clinker by replacing the sand and gravel aggregates with fly ash, ash, coke, coal, etc. Lightweight aerated blocks are a mixture of sand, cement, aluminum powder and water.
Additives are usually added to concrete mixes to give the blocks durable, water-repellent and coloring properties. The proportions in which the materials are mixed and the methods of production are instrumental in creating blocks of varying strengths and textures. The mixing and production is done by machines.
In the manufacturing process, concrete mixes that are damp or with very little water are fed into machine moulds, compacted and vibrated. Subsequently they are polymerized at high temperature and left to solidify. The masonry blocks are then ready to be used in construction.
Masonry block construction is fast and compatible with conventional masonry supplies. It requires standard 3/8 inch (0.95 cm) mortar joints and hollow cores can be reinforced with steel or concrete where required. A block wall structure provides excellent thermal and acoustic insulation and is usually painted or stuccoed for aesthetic appeal and protection from the elements.
It is best to seek professional advice and consult local building codes before starting construction. Different areas have different rules on the use of masonry blocks. In some parts of the United States, for example, cinder blocks are not permitted for foundations, while in the UK the use of cinder blocks has been discontinued.
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