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436 Barry’s Advanced Construction of Buildings
generally dictate the need to allow some movement of joints and fixings. There will be, for
example, very considerable temperature differences between facing slabs on an exposed
south-facing wall and the structure behind so that differential thermal movement has to
be allowed for both in joints and support and restraint fixings.
A general recommendation in the fixing of stone facing slabs is that there should be
horizontal movement joints at each storey height below loadbearing support fixings or not
more than 3 m. These joints are usually 10–15 mm deep and filled with one of the elastic
sealants. Where so wide a joint would not be acceptable in facework finished with narrow
joints, it is usual to accommodate movement in narrower sealant-filled horizontal joints to
all the facework. Vertical movement joints are formed in facework where these joints occur
in the structure, to allow for longitudinal structural, thermal and moisture movements. A
continuous vertical joint is formed between stone facings and filled with sealant.
Faience slabwork
Faience is the term used to describe fire glazed stoneware in the form of slabs that are used
as a facing to a solid background wall. Slabs are fixed in the same way as stone facings. The
best quality slabs are made from stoneware that shrinks and deforms less on firing than
does earthenware. The fired slab is glazed and then refired to produce a fire glazed finish.
The slabs are usually 300 × 200, 450 × 300 or 610 × 450 mm and 25–32 mm thick. They
form a durable, decorative facing to solid walls. The glazed finish, which will retain its lustre
and colour indefinitely, needs periodic cleaning, especially in polluted atmospheres. Faience
slabwork was much used as a facing in the 1930s in the UK, as a facing to large buildings
such as cinemas.
Terracotta
Terracotta was much used in Victorian buildings as a facing because it is less affected by
polluted atmospheres than natural limestone and sandstone facings. Fired blocks of terracotta,
with a semi-glaze self-finish, were moulded in the form of natural stone blocks to
replicate the form and detail of the stonework buildings of the time. The plain and ornamental
blocks were made hollow to reduce and control shrinkage of the clay during firing.
In use the hollows in the blocks were filled with concrete and the blocks were then laid as
if they were natural stone. This labour-intensive system of facing is still used today.
Tiles and mosaic
‘Tile’ is the term used to describe comparatively thin, small slabs of burnt clay or cast
concrete up to about 300 mm square and 12 mm thick. These small units of fired clay and
cast concrete are used as a facing to structural frames and solid background walls. For
many years, the practice has been to bond tiles directly to frames and walls with cement
mortar dabs, which provides sufficient adhesion to maintain individual tiles in place.
Unfortunately, this system of adhesion does not make any allowance for differential movements
between the frame, background walls and tiles, other than in the joints between tiles,
which can be considerable, particularly with in situ cast concrete work. To make allowance
for movements in the structure and the facing, tiles should be supported and restrained by
cramps that provide a degree of flexibility between the facing and the background. For