A composition that is applied between bricks and stones to cement them together (as in a wall) or that is used as a wall coating. (Le 14:42, 45; 1Ch 29:2; Isa 54:11; Jer 43:9) A weather-resistant mixture (properly termed “mortar”) of lime, sand, and water was used in the construction of the finer homes in ancient Palestine. Another type of mortar, used as plaster, was prepared by blending sand, ashes, and lime. Sometimes oil was added to the mixture, or the wall was coated with oil after it was plastered, to produce a nearly waterproof surface. In Egypt (even up to modern times) mortar used for wall plaster has been composed of two parts clay, one part lime, and one part straw and ashes.

Instead of conventional mortar, the builders of the Tower of Babel used bitumen, which “served as mortar for them.” (Ge 11:3) The later Babylonians likely obtained their bitumen for mortar from the subterranean fountains near the city of Hit located not far from Babylon on the Euphrates River. According to Herodotus (I, 179), hot asphalt (bitumen) was used as cement, or mortar, when building up the sides of Babylon’s moat and when constructing the city’s wall.

While the Israelites were slaves in Egypt, the Egyptians “kept making their life bitter with hard slavery at clay mortar and bricks.” (Ex 1:14) The mortar was mixed to about the consistency of molasses, usually by trampling it with the feet. Chopped straw was combined with the mortar to increase the cohesiveness of the mixture. Later, in their own land, clay mortar and mud bricks served the Israelites as basic building materials in areas where little good-quality building stone was available.

Mud bricks were not lastingly resistant to wet weather. Therefore, in order to protect a new wall or to save and strengthen a damaged wall, a coat of mortar, or plaster, was sometimes applied. However, if only whitewash or bad mortar containing little or no lime was daubed on such a wall, it could not be expected to withstand severe storms.​—Compare Eze 13:11-16.