eaded openings instead of or in conjunction
with arches. They are useful to preserve the square form and receive the
joiners' fittings, but except when made of steel or of concrete reinforced
with steel bars, they should have relieving arches turned immediately over
them (Fig.15).

"Fixing bricks" were formerly of wood of the same size as the ordinary
brick, and built into the wall as required for fixing joinery. Owing to
their liability to shrinkage and decay, their use is now practically
abandoned, their place being taken by bricks of coke-breeze concrete, which
do not shrink or rot and hold fast nails or screws driven into them.
Another method often adopted for [v.04 p.0527] providing a fixing for
joinery is to build in wood slips the thickness of a joint and 41/2 in. wide.
When suitable provision for fixing has not been made, wood plugs are driven
into the joints of the bricks. Great care must be taken in driving these in
the joints of reveals or at the corners of walls, or damage may be done.

The name "brick-ashlar" is given to walls faced with ashlar stonework
backed in with brickwork. Such constructions are liable in an aggravated
degree to the unequal settling and its attendant evils pointed out as
existing in walls built with different qualities of bricks. The outer face
is composed of unyielding stone with few and very thin joints, which
perhaps do not occupy more than a hundredth part of its height, while the
back is built up of bricks with about one-eighth its height composed of
mortar joints, that is, of a material that by its nature and manner of
application must both shrink in drying and yield to pressure. To obviate
this tendency to settle and thus cause the bulging of the face or failure
of the wall, the mortar used should be composed of Portland cement and sand
with a large proportion of the former, and worked as stiff as it
conveniently can be. In building such work the stones should be in height
equal to an exact number of brick courses. It is a common practice in
erecting buildings with a facing of Kentish rag rubble to back up the
stonework with bricks. Owing to the great irregularity of the stones, great
difficulty is experienced in obtaining proper bond between the two
materials. Through bonding stones or headers should be frequently built in,
and the whole of the work executed in cement mortar to ensure stability.

Not the least important part of the bricklayer's art is the formation of
chimne