120 VETERINARY HYGIENE 



BUILDING MATERIALS. 



The following notes on building materials are confined to those 

 in general use for ordinary farm buildings. There is a great variety 

 of proprietary articles made, many of which are good and useful, 

 but these, owing to their cost, are out of the question in most 

 agricultural buildings. 



BRICKS. Bricks are probably the oldest form of standardised 

 building material. Modern bricks are made either of a natural 

 clay or a suitable brick earth. To the former must be added any 

 of the necessary ingredients in which it is deficient. All clays and 

 brick earths vary in character. Natural plastic clays are composed 

 of silica and alumina, and contain a very small proportion of lime, 

 magnesia, sodium and other salts. They are inclined to shrink 

 if used alone, and attain great hardness when burned. 



Brick Earth or loam consists of clay (i.e., silicate of alumina) 

 and sand. The latter prevents shrinkage and cracking, but reduces 

 the hardness of the resultant brick. Most loams require the 

 addition of lime as a flux, in order that the materials may be bound 

 together. Marls or calcareous clays contain a large proportion 

 of chalk. Suitable brick earths, whether natural or artificial, should 

 contain such proportions of carbonate of lime and oxide of iron, &c., 

 as will form a sufficient flux to fuse the constituents when in the 

 furnace, but an excessive quantity will cause them to run together, 

 and result in an over-burned and badly-shaped brick. The oxide 

 of iron in a brick helps to bind the brick, and gives it its colour, 

 whilst the carbonate of lime is purely a binding material. 



Bricks should be of regular and uniform size, shape, texture and 

 colour, quickly and thoroughly burned right through. They should 

 be free from cracks and flaws, sharp on the arrises, and give out a 

 clear ringing sound when struck with a hard material. It being 

 impossible to receive delivery of all bricks in this perfect condition, 

 those slightly damaged are quite good for building in concealed 

 positions, provided that the brick is hard and well-burned. Moder- 

 ately rough, irregular and chipped bricks need not be objected to for 

 partitions or walls which have subsequently to be plastered or 

 covered in any way. Porous bricks should never be used in founda- 

 tions nor in external walls. They are sure to absorb' water, and 

 likely to weather badly. It is economical to build the brickwork 

 of agricultural buildings in cement mortar, as it results in much 

 more durable and water-resisting work, reducing depreciation and 

 giving a stronger result than the use of lime mortar. 



Ordinary building bricks of the best quality should be selected 



