Mortar is the ‘chemical glue’ and ‘gap-filling adhesive’ that holds masonry structures together. Its purpose is to even out any slight irregularities in brick shape and size and it has a direct influence on compressive strength, durability and resistance to rain penetration through brick walling. On this basis it is as fundamental to the construction of a wall as the bricks or blocks themselves.
In basic terms, mortar is a mixture of an aggregate (soft sand or builders’ sand), a binder (usually Ordinary Portland cement) and water. Additives such as plasticizers and pigments can be added in order to achieve a particular performance objective. Water is added to form a paste with the cement, which covers the surface area of every sand particle in the mix, binding the particles together to form a solid mass when the mortar hardens. The sand is not physically altered in any way, but is firmly set into the hardened, rock-like cement paste.