Plastering consists in applying different compositions resembling mortar to walls and ceilings, in thin layers, so as to form smooth surfaces, for the sake of appearance and cleanliness.

The plaster may either be laid on the face of the wall itself, or it may be spread over a screen of laths fixed in any required position.

The latter operation only is technically known as "plastering" the application to the wall itself being called "rendering."

Plastering and rendering are applied in one, two, or three coats, according to the importance of the building and the degree of finish required.

Materials Used By The Plasterer

The materials used for plastering will be fully described in Part III.

In the following brief notes information is given sufficient only to enable the student to understand the processes described in this chapter.

Limes And Cements. - Lime

The pure or fat limes are generally used for plastering, because in using hydraulic limes minute unslaked particles are apt to get into the work, and to blow, throwing out bits of plaster, and injuring the surface.

Plaster of Paris is calcined gypsum. When mixed with water to form a paste it sets very quickly, expanding as it sets, and attains its full strength in an hour or two.

Portland Cement is made from chalk and clay mixed together in water, then burnt and ground. It is the strongest cement in use, but sets more slowly than the other varieties.

Roman Cement, Medina Cement, Harwich, Calderwood, Whitby, Mulgrave's, and Atkinson's Cement, are all natural cements of the same description. They are made by burning nodules found in different geological formations. These cements set very rapidly, but attain no great ultimate strength.

Keene's, Parian, Martin's, and Robinson's Cements, are all manufactured by recalcining plaster of Paris with different substances.

These cements are useful only for indoor work; they set very quickly, and can be painted within a few hours.

Whiting is made by grinding white chalk to a fine powder.

Sand And Water

Very clean sand and fresh water should be used for plasterers' work (see Part III.)

Mixtukes

Coarse, Stuff is a rough mortar, containing 1 or 1 part of sand to 1 of lime by measure, thoroughly mixed with long ox hair (free from grease and dirt), in the proportion of 1 lb. hair to 3 cubic feet of mortar.

Fine Stuff is pure lime slaked with a small quantity of water, and afterwards saturated until it is of the consistence of cream; it is then allowed to settle and the water to evaporate, until thick enough for use. For some purposes a small quantity of white hair is added.

Plasterers' Putty is lime dissolved in water, and then run through a hair sieve. It is very similar to fine stuff, but prepared somewhat differently, and always used without hair.

Gauged Stuff consists of from to 4/5 plasterers' putty, and the remainder plaster of Paris. The last-named ingredient causes the mixture to set very quickly, and it must be gauged in small quantities. The proportion of plaster used depends upon the time to be allowed for setting, the state of the weather, etc., more time required in proportion as the weather is damp.

For cornices the putty and plaster are often mixed in equal proportions.

Stucco is a term vaguely applied to many mixtures containing common and hydraulic limes, also to some cements.

Common Stucco contains three or four parts sand to one of hydraulic lime.

Trowelled Stucco consists of 2/3 fine stuff (without hair), and 1/3 very fine clean sand.

Bastard Stucco is of same composition as trowelled stucco, with the addition of a little hair.

Rough Cast consists of sand, grit, or gravel, mixed with hot lime in a semi-fluid state.

Size is thin glue made by boiling down horns, skins, etc.

Double Size is boiled for a greater time so as to be stronger.

Laths are thin strips of wood, generally fir, sometimes oak, split from the log, 3 or 4 feet long, about an inch wide, and varying in thickness according to their class.

Single laths are about...................

3/16

inch thick.

Lath-and-half lath „....................

"

Double laths "............................................

3/8

"