A plasterer is a tradesperson who works with plaster, such as forming a layer of plaster on an interior wall or plaster decorative moldings on ceilings or walls. The process of creating plasterwork, called plastering, has been used in building construction for centuries.
History
Plasterwork is one of the most ancient of handicrafts employed in connection with building operations, the earliest evidence showing that the dwellings of primitive man were erected in a simple fashion with sticks and plastered with mud. Soon a more lasting and sightly material was found and employed to take the place of mud or slime, and that perfection in the compounding of plastering materials was approached at a very remote period is made evident by the fact that some of the earliest plastering which has remained undisturbed excels in its scientific composition that which we use at the present day. The pyramids in Egypt contain plasterwork executed at least four thousand years ago, probably much earlier, and yet existing, hard and durable, at the present time. From recent discoveries it has been ascertained that the principal tools of the plasterer of that time were practically identical in design, shape and purpose with those used today. For their finest work the Egyptians used a plaster made from calcined gypsum just like plaster of Paris of the present time, and their methods of plastering on reeds resemble in every way our lath, plaster, float and set work. Hair was introduced to strengthen the stuff, and the whole finished somewhat under an inch thick. Very early in the history of Greek architecture we find the use of plaster of a fine white lime stucco, such has been found at Mycenae. The art had reached perfection in Greece more than five centuries before Christ, and plaster was frequently used to cover temples externally and internally, in some cases even where the building was of marble. It formed a splendid ground for decorative painting, which at this period of Grecian history had reached a very high degree of beauty. Also known as Gyporockers.
Tools and materials In the more common operations of plastering, comparatively few tools and few materials are required, but the workman efficient in all branches of the craft will possess a very large variety of implements. The materials of the workman are laths, lath nails, lime, sand, hair, plaster of Paris, and a variety of cements, together with various ingredients to form coloring washes, et cetera.
Laths
Wood laths are narrow strips of some straight-grained wood, generally Baltic or American fir, in lengths of from two to four or five feet to suit the distances at which the timbers of a floor or partition are set. Laths are about an inch wide, and are made in three thicknesses; single (1/8 to 3/16 inch thick), lath and a half (1/4 inch thick), and double (3/8–1/2 inch thick). The thicker laths should be used in ceilings, to stand the extra strain, and the thinner variety in vertical work such as partitions, except where the latter will be subjected to rough usage, in which case thicker laths become necessary. Laths are usually nailed with a space of about 3/8 of an inch between them to form a plaster key. Laths were formerly all made by hand. A large quantity, however, are now made by machinery and are known as sawn laths, those made by hand being called rent or riven laths. Rent (riven) laths give the best results, as they split in a line with the grain of the wood, and are stronger and not so liable to twist as machine-made laths, some of the fibers of which are usually cut in the process of sawing. Care should be taken to check the pH value of the wood; oak contains tannic acid which attacks the lime, this can compromise bond strength. Laths must be nailed so as to break joint in bays three or four feet wide with ends butted one against the other. By breaking the joints of the lathing in this way, the tendency for the plaster to crack along the line of joints is diminished and a better key is obtained and it provides restraint for the timber frame. Every lath should be nailed at each end and wherever it crosses a joist or stud. All timbers over three inches (76 mm) wide should be counter-lathed, that is, have a fillet or double lath nailed along the centre upon which the laths are then nailed. This is done to preserve a good key for the plaster. Walls liable to damp are sometimes battened and lathed in order to form an air cavity between the damp wall and the plastering. Lathing of metal, either of wire or in the form of perforated sheets, is now extensively used on account of its fireproof and lasting quality. There are very many kinds of this material Metal made in different designs under various patents, the best known in England being the Jhilmil, the Bostwick, Lathing, and the Expanded Metal lathing. The two last-named are also widely used in America. Lathing nails are usually of iron, cut, wrought or cast, and in the better class of work they are galvanized to prevent rusting. Zinc nails are sometimes used, but are costly.
Lime The lime principally used for internal plastering is that calcined from chalk, oyster shells or other nearly pure limestone, and is known as fat, pure, chalk or rich lime. Hydraulic limes are also used by the plasterer, chiefly for external work. Perfect slaking of the calcined lime before being used is very important as, if used in a partially slaked condition, it will "blow" when in position and blister the work. Lime should therefore be run as soon as the building is begun, and at least three weeks should elapse between the operation of running the lime and its use. Due to time constraints Hydrated Lime mixed with plaster is normally used for modern construction. Slaking is not required if more time is allowed for finishing the surface after application which is a common practice where a quality finish is required, however in the housing industry it is often run for three days, the time it takes to prepare an average house for plastering, to achieve a lower quality cost effective finish.
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