lightweight, and when finished measures only from two to four inches (102 mm) thick. So strong is the result that partitions of this class only two or three inches (76 mm) thick were used for temporary cells for prisoners at Newgate Gaol during the rebuilding of the new sessions house in the Old Bailey in London. The slabs may be obtained either with a keyed surface, which requires finishing with a setting coat when the partition or ceiling is in position, or a smooth finished face, which may be papered or painted immediately the joints have been carefully made. Fibrous plaster Fibrous plaster is given by plasterers the suggestive name "stick and rag", and this is a rough description of the material, for it is a fibrous composed of plaster laid upon a backing of canvas stretched on wood. It is much used for moldings, circular and enriched casings to columns and girders and ornamental work, which is worked in the shop and fixed in position. Desachy, a French modeler, took out in 1856 a patent for "producing architectural moldings, ornaments and other works of art, with surfaces of plaster," with the aid of plaster, glue, wood, wire, and canvas or other woven fabric. The modern use of this material may be said to have started then, but the use of fibrous plaster was known and practiced by the Egyptians long before the Christian era; for ancient coffins and mummies still preserved prove that linen stiffened with plaster was used for decorating coffins and making masks. Cennino Cennini, writing in 1437, says that fine linen soaked in glue and plaster and laid on wood was used for forming grounds for painting. Canvas and mortar were in general use in Great Britain up to the middle of the 20th century. This work is also much used for temporary work, such as exhibition buildings. Plastering Modern interior plastering techniques There are two main methods in USA used in construction of the interior walls of modern homes, plasterboard, also called drywall, and veneer plastering. In plasterboard a specialized form of sheet rock known as "greenboard" (because on the outer paper coating is greenish) is screwed onto the wall-frames (studs) of the home to form the interior walls. At the place where the two edges of wallboards meet there is a seam. These seams are covered with mesh tape and then the seams and