LIME PLASTERING 107 



clean sand should be used, it is seldom that such is obtainable, there being 

 generally more or less clay present. The presence of too much clay results 

 in cracking of the plaster coating as it dries. 



Too large a proportion of lime also causes cracking, especially if the 

 sand is clayey, in which case it may be necessary to make the propor- 

 tions leaner than 1 to 3. 



Before applying the plaster to the wall, the mortar in the joints 

 between the bricks should be well raked out with the point of a trowel 

 to a depth of f inch. The brickwork and raked-out joints should then 

 be brushed clean, and well wetted to prevent the moisture being absorbed 

 too quickly from the plaster, and also to remove dust which would 

 prevent proper adhesion of the plaster to the brickwork. In applying 

 the plaster to the wet brickwork, it should be well pressed into the 

 raked-out joints with the trowel. 



In South Africa, plaster is usually applied in one coat, though in the 

 case of a rough stone wall a sort of preliminary coat is often applied, 

 in order to fill up depressions, before the application of the final coat. 



A reference to the Chapter on cement concrete (Chap. XIII., p. 134) 

 will give the reader some idea of the method adopted by the plasterer in 

 applying the plaster. 



Plaster on external walls, which has to resist the weather, should not 

 be less than £-inch thick, though f -inch is to be preferred. 



Plaster for Unburned Bricks. — Sun-dried, unburned bricks may be 

 plastered as follows : — 



Mix one part cow-dung and two parts sandy loam (by volume 

 thoroughly with water. Allow the mixture to stand for a few days, 

 then mix it up again thoroughly just before applying it to the wall. 



The joints between the bricks should be raked out to a depth of 

 about | inch, but the brickwork should not be wetted before applying the 

 plaster. 



Apply the plaster to a thickness of not more than j-inch, pressing 

 it well into the raked-out joints, and leaving the surface rough. This 

 first coat should be left until it has become quite dry and hard, which 

 will be in one or two weeks. 



A second coat of a similar composition to the first, except that it 

 contains a slightly greater proportion of sandy loam to make it harder 

 when dry, is then applied to a thickness of about -g inch, and is finished 

 off as smooth as possible with a wooden float. 



