Mortar is a workable paste which hardens to bind building blocks such as stones, bricks, and concrete masonry units, to fill and seal the irregular gaps between them, spread the weight of them evenly, and sometimes to add decorative colors or patterns to masonry walls. In its broadest sense, mortar includes pitch, asphalt, and soft mud or clay, as used between mud bricks. The word “mortar” comes from Latin mortarium, meaning crushed. Cement mortar becomes hard when it cures, resulting in a rigid aggregate structure; however, the mortar functions as a weaker component than the building blocks and serves as the sacrificial element in the masonry, because mortar is easier and less expensive to repair than the building blocks. Bricklayers typically make mortars using a mixture of sand, a binder, and water. The most common binder since the early 20th century is Portland cement, but the ancient binder lime mortar is still used in some specialty new construction.
Mortar (masonry) Damp Proofing
Water drawn up from underlying soils and rocks holds dissolved salts. As the saline liquid evaporates, generally over a 6 to 12 month period, crystallised salts remain both in the wall and in its plastered surface. The accumulation of salt crystals degrades the masonry, mortar and the wall plaster. As salts are typically hygroscopic, they absorb moisture from the air, especially under humid conditions. This salt damp alone can cause the wall and any contacting decorations to remain damp even after the provision of a new DPC. To comply with BS 6576 fully:2005+A1:2012, replacing salt contaminated wall plaster with a salt resistant plaster mix is an essential requirement in the treatment of rising damp. At least 14 days should elapse between injection of the DPC and the application of new plaster unless using an air-gap membrane to isolate brickwork and salts from the plaster finishes during the drying process.
Mortar (masonry) Rendering
Mortar can generally be thought of as a glue that fills gaps, which will even out uneven and irregular wall surfaces, bind blocks and bricks together in the construction of a wall, and also as rendering to achieve a smooth and weatherproof finish. The correct mix to use when applying rendering should be more or less ONE part of cement to FOUR parts of sand. This mix can vary slightly, depending on the porosity of the wall and the material the wall is made from.
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