Ashlar is stonework that is cut on at least four sides, so that the when it is laid, it joins with the other stones at right angles. The face of ashlar masonry can be dressed or unfinished. This type of masonry dates back to at least the time of ancient Egypt. An early example of it can be seen on the step pyramid of Djoser, which dates back to the 27th century BC.
This dressed stone typically comes in a range of styles and sizes. Its height can be as little as two inches (5.08 cm) to as great as 16 inches (40.64 cm). Its width varies similarly. Ashlar’s face — or the side that can be seen when looking at a constructed wall — can be left rough, chiseled to achieve textures, chamfered or beveled at the edges, or completely smoothed and, sometimes, polished. The joints are often very narrow and barely visible. Some types of stone commonly used in this form of masonry include granite, limestone, and English Portland stone.
Ashlar masonry can be laid in straight or broken courses. Straight courses resemble rows, while broken courses present a more random look. Whichever way ashlar is laid, however, care needs to be take to keep horizontal bed joints level, and vertical joints plumb. Uneven joints are often visually noticeable and can detract from the appearance of the stonework.
Buildings that employ this type of masonry are often meant to convey great importance or solidity. Some examples that typically utilize ashlar include banks, government buildings, churches, and schools. It can also be seen in monuments and some bridges.
Various names have been given to the different patterns in which this stonework can be laid. For example, coursed ashlar uses stone blocks that are uniform in size and are laid in continuous horizontal bed joints. This effect creates uniform rows of stone, all the same height. Variation occurs with the vertical joints between two rows of stone. Every vertical joint is offset between adjoining rows, but the joints line up between every other row.
Ashlar can be expensive compared to other types of masonry, such as block, brick, or rubble. For this reason, it is often used to face walls. The backing is usually made of a less expensive stone or brick, which is laid first. Then a thinner veneer of the dressed stone is applied to the front of the backing.