cks_, for cornices, string courses, plinths, labels and
copings. They are made in the different classes to many patterns; and on
account of their greater durability, and the saving of the labour of
cutting, are preferable in many cases to rubbers. For sewer work and
arches, bricks shaped as voussoirs are supplied.

The strength of brickwork varies very considerably according to the kind of
brick used, the position in which it is used, the kind and [Sidenote:
Strength of brickwork.] quality of the lime or cement mortar, and above all
the quality of the workmanship. The results of experiments with short walls
carried out in 1896-1897 by the Royal Institute of British Architects to
determine the average loads per sq. ft. at which crushing took place, may
be briefly summarized as follows: Stock brickwork in lime mortar crushed
under a pressure of 18.63 tons per sq. ft., and in cement mortar under
39.29 tons per sq. ft. Gault brickwork in lime mortar crushed at 31.14
tons, and in cement mortar at 51.34 tons. Fletton brickwork in lime crushed
under a load of 30.68 tons, in cement under 56.25 tons. Leicester red
brickwork in lime mortar crushed at 45.36 tons per sq. ft., in cement
mortar at 83.36 tons. Staffordshire blue brick work in lime mortar crushed
at 114.34 tons, and in cement mortar at 135.43 tons.

The height of a brick pier should not exceed twelve times its least width.
The London Building Act in the first schedule prescribes that in buildings
not public, or of the warehouse class, in no storey shall any external or
party walls exceed in height sixteen times the thickness. In buildings of
the warehouse class, the height of these walls shall not exceed fourteen
times the thickness.

In exposed situations it is necessary to strengthen the buildings by
increasing the thickness of walls and parapets, and to provide heavier
copings and flashings. Special precautions, too, must be observed in the
fixing of copings, chimney pots, ridges and hips. The greatest wind
pressure experienced in England may be taken at 56 lb on a sq. ft., but
this is only in the most exposed positions in the country or on a sea
front. Forty pounds is a sufficient allowance in most cases, and where
there is protection by surrounding trees or buildings 28 lb per sq. ft. is
all that needs to be provided against.

In mixing mortar, particular attention must be paid to the sand with which
the lime or cement is mixed. The best sand is that [Sidenote: