PLASTER. The Egyptians plastered their stone buildings, even the finest granite, inside and out, to make a smooth surface for decoration. The poor used a mixture of clay and straw. On better buildings the first coat was gypsum and red clay or ashes, the finish coat slaked lime and white sand, sometimes including chopped straw. In Palestine and Syria, an outside clay coating had to be renewed after the rainy reason. Mortar was usually made with limestone, the process of its manufacture otherwise similar to that in Egypt. The Arabic word for mortar means “clay.” Hebrew sîdh (Deut.27.2, Deut.27.4) means “to boil up,” because of the action when water is poured on unslaked lime. Hebrew gîr (Dan.5.5) means “burned in a kiln” (either lime or gypsum). Tûah (Lev.14.42-Lev.14.48) means “to daub, smear.”
International Standard Bible Encyclopedia (1915)
In Egypt, now as in ancient times, the buildings are plastered inside and out. The poor quality of the stone commonly used makes this necessary if a smooth attractive surface is desired. Among the poorer classes, clay mixed with straw is used. In Palestine and Syria, where there is a rainy season, the coating on the outside walls, if made of clay, must be frequently renewed. In Egypt burnt gypsum, and in Palestine and Syria burnt limestone (lime) are the commonest materials for making mortar. For the first coat of plastering the lime is mixed with "fat" red sand or with the ash from the bathhouse fires, and the finishing coat is composed of white sand and slaked lime with or without chopped flax straw. The plaster on some of the ancient Egyptian ruins seems to indicate that milk or some similar substance was added to the mortar to give a better surface.
The ancients preferred plastered surfaces for decorating, and even the finest granite was covered with stucco on which to paint or carve the decorations (De 27:2; Da 5:5). Columns were often first stuccoed and then painted.
The Arabic word for mortar is Tin, which really means "clay." The Hebrew sidh, literally, "to boil up," refers to the boiling of the water with which the lime is slaked, because of the heat generated during the slaking process. In Da 5:5 occurs gir, i.e. "burned in a kiln," which might mean either lime or gypsum. In Le 14:42 occurs Tuach, "to smear."
James A. Patch
Only used in Isa 38:21 of the application of the cake of figs to the boil from which Hezekiah suffered. In Papyrus Ebers, figs are used as the ingredient in a plaster (xxxv, lxxix, lxxxiii). Dioscorides also recommends figs with other substances as a poultice in some skin diseases.