Page:EB1911 - Volume 21.djvu/817

Rh stuff, or lime putty, is pure lime which has been slaked and then mixed with water to a semi-fluid consistency, and allowed to stand until it has developed into a soft paste. For use in setting it is mixed with fine washed sand in the ratio of one to three.

For cornices and for setting when the second coat is not allowed time to dry properly, a special compound must be used. This is often “gauged” stuff, composed of three or four parts of lime putty and one part of plaster of Paris, mixed up in small quantities immediately before use. The plaster in the material causes it to set rapidly, but if it is present in too large a proportion the work will crack in setting.

The hard cements used for plastering, such as Parian, Keene’s, and Martin’s, are laid generally in two coats, the first of cement and sand to  in. in thickness, the second or setting coat of neat cement about in. thick. These and similar cements have gypsum as a base, to which a certain proportion of another substance, such as alum, borax or carbonate of soda, is added, and the whole baked or calcined at a low temperature. The plaster they contain causes them to set quickly with a very hard smooth surface, which may be painted or papered within a few hours of its being finished.

The by-laws made by the London County Council under § 31 of the London Council (General Powers) Act 1890 set forth the description and quality of the substances of which plastering is to be made for use in buildings erected under its jurisdiction.

Plain, or unenriched, mouldings are formed with a running mould of zinc cut to the required profile. Enrichments may be

added after the main outline moulding is set, and are cast in moulds made of gelatine or plaster of paris. For a cornice moulding two running rules are usual, one on the wall, the other on the ceiling, upon which the mould is worked to and fro by one workman, while another man roughly lays on the plaster to the shape of the moulding. The mitres at the angles are finished off with joint rules made of sheet steel of various lengths, three or four inches wide, and about one-eighth inch thick, with one end cut to an angle of about 30°. In some cases the steel plate is let into a “stock” or handle of hardwood.

Cracks in plastering may be caused by settlement of the building, and by the use of inferior materials or by bad workmanship, but

apart from these causes, and taking the materials and labour as being of the best, cracks may yet ensue by the too fast drying of the work, caused through the laying of plaster on dry walls which suck from the composition the moisture required to enable it to set, by the application of external heat or the heat of the sun, by the laying of a coat upon one which has not properly set, the cracking in this case being caused by unequal contraction, or by the use of too small a proportion of sand.

For partitions and ceilings, plaster slabs are now in very general use when work has to be finished quickly. For ceilings they require

simply to be nailed to the joists, the joints being made with plaster, and the whole finished with a thin setting coat. In some cases, with fire-proof floors, for instance, the slabs are hung up with wire hangers so as to allow a space of several inches between the soffit of the concrete floor and the ceiling. For partitions the slabs frequently have the edges tongued and grooved to form a better connexion; often, too, they are holed through vertically, so that, when grouted in with semi-fluid plaster, the whole partition is bound together, as it were, with plaster dowels. Where very great strength is required the work may be reinforced by small iron rods through the slabs. This forms a very strong and rigid partition which is at the same time fire-resisting and of light weight, and when finished measures only from two to four inches thick. 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. Partitions are also formed with one or other of the forms of metal lathing previously referred to, fixed to iron uprights and plastered on both sides. So strong is the result that partitions of this class only two or three inches thick were used for temporary cells for prisoners at Newgate Gaol during the rebuilding of the new sessions house in the Old Bailey, London.

Fibrous plaster is given by plasterers the suggestive name “stick and rag,” and this is a rough description of the material, for it is

composed of plaster laid upon a backing of canvas stretched on wood. It is much used for mouldings, circular and enriched casings to columns and girders and ornamental work, which, being worked in the shop and then nailed or otherwise fixed in position, saves the delay often attendant upon the working of ornament in position.

Desachy, a French modeller, took out in 1856 a patent for “producing architectural mouldings, 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 practised 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 last century. This work is also much used for temporary work, such as exhibition buildings.

The principal books of reference on the subject are: W. Millar, Plastering, Plain and Decorative; G. R. Burnell, Limes, Cements, Mortars and Mastics; Rivington, Notes on Building Construction, Part III. “Building Materials”; the works on architecture of Robert and James Adam.

 PLATA, RIO DE LA, or, a funnel-shaped estuary, on the east side of South America, extending W.N.W. from the sea about 170 m. The discovery of the South Sea by Balboa, then governor of Castilla del Oro, of which Darien formed a part, created a lively desire to learn something of its coast-line, and the year following (in 1514), the Spanish monarch concluded a navigation contract with Juan Diaz de Solis, then Piloto Mayor, to search for a strait connecting the Atlantic with the newly found ocean, explore the coasts of the latter and communicate with Pedrarias de Avila, the new governor of Castilla del Oro; and, if it were found to be an island, to report to the superior authorities of Cuba. De Solis set sail from the port of Lepe on the 8th of October 1515, reached the Bay of Rio de Janeiro on the 1st of January 1516, and continuing southward to lat. 35° entered the great estuary now known as the Plata, which, for a short period of time, was called the de Solis and the Mar Dulce. Ascending it to the vicinity of the island of Martin Garcia, near the mouth of the Paraná river, de Solis was ambushed and killed in the early part of 1516 by Guarani Indians while attempting to capture some of them. In the first months of 1520 Magellan explored the Rio de la Plata, and afterwards, in the same year, discovered and navigated the straits which bear his name. This discovery led to the voyage of Sebastian Cabot, who fitted out an expedition in 1526 to reach the Spice Islands by the Magellan route. Owing, however, to shortness of provisions and the insubordination of his men Cabot abandoned his proposed voyage to the Moluccas, and, ascending the Mar Dulce, discovered the Paraná river and reached a point on the Paraguay near the site of the present city of Asuncion. Here he met many Guarani Indians wearing silver ornaments, probably obtained in trade across the Gran Chaco, from the frontier of the Inca Empire. In exchange for beads and trinkets Cabot acquired many of these ornaments and sent them to Spain as evidence of the richness of the country in precious metals and the great importance of his discoveries. The receipt of these silver baubles caused the name of Rio de la Plata to be applied to the third (perhaps the second) greatest river of the Western Continent.

The extreme breadth of the river at its mouth is 138 m. It narrows quickly to 57 m. at Montevideo, and at its head, where it receives the united Paraná and Uruguay rivers, its width is about 25 m. Its northern or Uruguayan shore is somewhat elevated and rocky, while the southern or Buenos Airean one is very low. The whole estuary is very shallow, and in no place above Montevideo exceeds 36 ft. in depth when the river is low. The bottom generally consists of enormous banks of sand covered with from 10 to 20 ft. of water, and there is a continuous and intricate channel, of about 22 ft. depth only, to within 14 m. of the port of Buenos Aires. The remaining distance has a depth of 18 ft. in the uncertain channel. The Plata is simply the estuarine receptacle of two mighty streams, the Uruguay and Paraná, which drain the Plata basin. This has an area of 1,198,000 sq. m., or over two and one-half times that of the Pacific slope of the Andes, and comprises the most fertile, healthiest and best part of Brazil, a large portion of the Argentine Republic, the whole of Paraguay and south-eastern Bolivia, and most of Uruguay.

The Uruguay river has a length of about 1000 m. Many small streams from the western slope of the Brazilian Serra do Mar unite, in about 27° 45′ S., to form this river, which then flows W.N.W., serving as the boundary between the states of Santa Catharina and Rio Grande do Sul, as far as 52° W., near which it receives a considerable tributary from the north, called the Pepiri-guazú. Between 27° 58′ and 33° 34′ S. three important tributaries join it from the east—the Ipui-guazú, the Ibicui and the Negro, the last being its main affluent.

