Concrete block is a building material made from Portland cement, sand, water and aggregate. It is used in place of poured concrete to construct walls, footers, foundations and many other structures. Concrete block is available in a number of different types to suit a variety of applications.
Concrete blocks are typically sold in standard 8" by 8" rectangles that are 16" long. They usually measure 3/8" smaller than their given measurements, which allows room for mortar application. These blocks may be solid or hollow core, with hollow units offering less strength and less weight. Concrete blocks are also known as concrete masonry units (CMU) or masonry blocks.
Standard concrete blocks come in two- and three-core varieties. The corners of each block extend slightly past the face to help conceal the mortar in the finished wall. Corner and end blocks do not have these extended edges, which produce a smooth look at edges and intersections. Sash units are precut to fit around windows, and jamb units are similarly precut to accommodate door frames. Capping blocks have a top layer designed to conceal the cores, and header units are designed to fit at the top of bottom of a window opening.
These blocks may be smooth or split-faced. A split-faced block has a rugged surface that adds texture to a building, though this type of block is much more expensive than smooth units. Blocks may be coloured with integral pigments or dyes and may also be bull-nosed, or rounded at the edges, to improve their appearance. Glazed blocks have a porcelain coating that makes them suitable for moisture-prone or sanitary applications.
When installing concrete blocks, the builder must decide whether to use a reinforced or non-reinforced technique. Reinforced block installations use steel rebar placed within the cores of each block to help increase strength and durability. Non-reinforced units do not use rebar or steel, and may not last as long as reinforced units.
Concrete block is installed over a concrete foundation and requires the use of masonry mortar between each row of blocks. The joints of each row are staggered to create a more stable structure. Blocks are cut with a masonry hammer and chisel to fit each row.
Concrete block offers a number of benefits when used to construct walls, foundations and other features. It is highly resistant to fire, insects and mould, and can be expected to last for many years with little to no maintenance. This material is much more economical than poured concrete. It can also be installed more rapidly, which can reduce labour and equipment costs associated with installation.