Plastering consists in covering with a smooth surface all rough walls, ceilings, partitions, etc., in the superior apartments of dwellings, etc., where a more finished, better-looking, and more sanitary effect is required. This result is obtained by the use of various materials, including several patents, as will be pointed out in the following remarks on the materials themselves and their application.
The lime used by the plasterer is the pure lime, containing only carbonate of lime, and is sometimes called a fat lime. It has neither great power of setting nor ultimate strength, is of a white colour, and slakes very freely; and immediately the water is poured on it a great volume of steam will arise, and the lime will begin to crack very loudly, if it is of the best kind for plastering.
Such lime is found at Crich, Buxton, and Dorking, being the product of burning either marble, white chalk, or the Bath and Portland oolites of various places. By the slaking process pure lime will increase in bulk to three times its original cubical contents. When the slaking is completed the lime and water are run through sieves, to collect and screen out the hard unslaked lumps or residue, which would be a source of danger in the finished work. The creamy mixture of slaked lime and water is called putty; and in this state, to ensure perfect slaking, some limes should be kept for a period of one or two months before being used.
The sand used for plastering must be clean and sharp, free from all earthy or vegetable matter, and washed, if necessary, to eliminate all these impurities. Pit sand is far preferable to that taken from large river beds, where the sand is continually kept in motion by the currents, so that the particles or grains are rounded, which takes away their sharpness.
Plasttr-of-PariSt used for gauged stuff, is calcined gypsum, which, after being mixed with water to a paste, sets quickly and with a smooth Hardened white surface.
Portland cement which will be dealt with more fully in Chapter XXIII (Miscellaneous Materials. Asphalte And Granite)., is chiefly used for outside work, the lighter (in weight) and quicker-setting qualities being the most suitable for this purpose.
Keent's cement is Plaster-of-Paris, saturated with alum, and is chiefly used for angles, pilasters, and the more ornamental parts of plastering, for internal use only.
Parian cement is a finer-working substance, used for large surfaces of a better class in internal plastering, the walls generally being first backed up or rendered over with Portland cement and sand, in preparation for the Parian, which is really Plaster-of-Paris recalcined, with borax added.
Martin's cement is similar to the last in preparation, pearl ash being used instead of borax, which produces a "fatter" cement, forming (like Keene's) a better "arris."
There are several other kinds of cement of these classes, but they are so seldom used in ordinary work that it is unnecessary to describe them.
The. laths used for plaster work (Fig. 881) are thin strips of wood, about 1 inch broad and up to 4 feet long, rent or sawn out of good fir or oak : and the different thicknesses are classified as below: -
Single lath are about 3/16 of an inch thick. Lath-and-half „ 1/4 „ „ „
Double lath „ 3/8 „ „ „