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the finished work. Plaster should
be firmly trowelled onto walls and
executed in one operation. Plaster
should be pushed onto the wall or
ceiling using pressure to compact
the plaster and to ensure full contact
with the substrate. Once applied the
plaster should stiffen.
It is important that the plaster
does not dry out too quickly and
should be dampened or sprayedwith
a light spray for a period of not less
than three days. Successive coats
should not be applied during this
time. Once the substrate coat has
hardened sufficiently another coat
can be applied.
INSTALLATION OF CLAY
AND CONCRETE ROOF
TILES
Mechanical fixing systems may com-
prise either singly or in combination,
mechanical fixings such as clips,
nails, screws and cement mortars.
Mortar for bedding and pointing
comprises one part common cement
and three parts sand and mixed in
accordance to specifications. Fixing
nails should penetrate battens to a
depth of not less than 25 mm.
Damage due to excessive gusting
occurs at eaves, verges and ridges.
Mechanical fixing systems prevent
tiles from being lifted off. All tiles
should be aligned vertically, hori-
zontally and diagonally and overlap
each other by the minimum amount
specified by the manufacturer, but
not less than 50 mm.
At the beginning of the tiling
operation, a course of tiles should
be laid along the roof from right to
left at the eaves and along the ridge.
This procedure will ensure that the
overhang of both verges, is equal. If
the tiles do not provide the desired
overhang at each gable end or do
not fit, the lock tolerance on each
tile should be opened or closed to
achieve the desired overhand. It may
be necessary to fix a cut tile at each
end of the roof. Once the overhang
has been achieved, it will thenbe pos-
sible to lay a course of tiles that are
true and straight both horizontally
and vertically. When this has been
established, the battens at the gable
end can be cut and verge counter bat-
tens (50 x 38 mm) installed.
Tiles in each course, or in each
alternate course, should be set out
in vertical alignment so that the tiling
presents a regular and even appear-
ance. All starters, finishers and full
tiles at the end of each course at a
gable should be mechanically fixed.
The cutting of tile ridges, hips,
verges and valleys shouldbe neat and
present a straight line. Tiles at ridges
and hips extend under the capping by
a sufficient distance to be weather-
proof. Similarly, tiles should overlap
valleys by a sufficient distance to be
weatherproofed.
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Reinforcement
Exposed trusses
Roof tiling