1. In modern practice, plastering occurs in many departments of architecture. It is more particularly applied to the ceilings and interior walls of buildings, and also in rough-casting on their exterior. 2. In plastering the interior parts of buildings, three coatings of mortar are commonly applied in succession. The mortar for the _first coat_ is composed of about twelve parts of sand, six of lime, and three of hair, with a sufficient quantity of water to bring it to the proper consistence; that for the _second coat_ contains a less proportion of lime and hair; and that for the _third coat_ is composed exclusively of lime and water. 3. The mortar is applied directly to the solid wall, or to thin strips of wood called _laths_, which have been fastened with small nails to the joists, and other parts of the frame of the building. The tools with which the plasterer applies the mortar are _trowels_ of different sizes and shapes, and the _hawk_. The latter instrument is a board about a foot square, with a short handle projecting at right angles from the bottom. 4. In all well-finished rooms, cornices are run at the junction of the wall and ceiling. The materials of these cornices are lime, water, and plaster. The lime and water are first incorporated, and the plaster is added with an additional quantity of water, as it may be needed for immediate application. The composition is applied in a semifluid state, but the plaster causes it _to set_, or to become solid immediately. In the mean time, the workman applies to it, in a progressive manner, the edge of a solid piece of wood, in which an exact profile of the proposed cornice has been cut. 5. Ornaments of irregular shape are cast in moulds of wax or plaster of Paris, and these are formed on models of the proposed figures in clay. Such ornaments were formerly the productions of manual operations performed by ingenious men called _ornamental plasterers_. The casts are all made of the purest plaster; and, after having been polished, they are fastened to the proper place with the same substance saturated with water. 6. The branch of this business called _rough-casting_, consists in applying mortar to the exterior walls of houses. The mode in which the work is performed varies but little from that adopted in plastering the walls of apartments. It, however, requires only two coats of the cement; and, when these have been applied, the surface is marked off in imitation of masonry. It is likewise sometimes colored, that it may resemble marble or some other stone. 7. The cement is commonly made of _sharp sand_ and lime; but sometimes a kind of argillaceous stone, calcined in kilns and afterwards reduced to powder by mechanical means, makes a part of the composition. The qualities of this material were first discovered by a Mr. Parker, who obtained letters patent for this application of it, in England, in 1796; hence it has been called _Parker's cement_. THE SLATER.