The concrete commonly used to make a concrete block, which is a mixture of powdered cement, water, sand, and gravel. This produces a light gray block with a fine surface texture and a high comprehensive strength. In general, the concrete mixture used for blocks has a higher percentage of sand and a lower percentage of gravel and water than the concrete mixtures used for general construction purposes. This produces a very dry, stiff mixture that holds its shape when it is removed from the block mold.
In addition to the basic components, the concrete mixture used to make blocks may also contain various chemicals, called admixtures, to alter curing time, increase comprehensive strength, or improve work-ability. The mixture may have pigments added to give the blocks a uniform color throughout, or the surface of the blocks may be coated with a baked-on glaze to give a decorative effect or to provide protection against chemical attack. The glazes are usually made with a somersetting resinous binder, silica sand, and color pigments.