Traditionally roof tile cappings have been bedded and pointed in
a sand-cement mortar. The mortar bed supports and aligns the capping
while the pointing provides the majority of adhesion and allows
a neat finish. Additional mechanical fixing is required in high
wind areas.
Being rigid, the mortar in conventional point may crack with the
movement of the roof structure. This is unsightly and can lead to
premature maintenance. Cracking may occur if pointing is disturbed
by nearby work such as television antenna installation.
Flexible pointing overcomes these problems. There are a number of
flexible pointing materials, each containing synthetic compounds.
Some are pre-coloured to match specific tiles, others are pigmented
by the tiler. Unlike conventional mortars, flexible pointing material
is trowelled to a consistent thickness of threw to five millimetres
and finished off to a smooth surface. Weep holes must be placed
in the usual positions.
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Flexible pointing
will generally take longer to cure that conventional mortar. Requirements
vary between products and with climatic conditions but usually two
to three hours of curing is adequate although caution should be
exercised is rain is expected. A manufacturer's application, handing
and safety requirements must be followed.
Although the concealed mortar be may still crack, the cured flexible
pointing will maintain the roof's integrity by absorbing considerable
movement without cracking.
Despite being relatively the veneer, flexible pointing provides
most of the capping adhesion. Flexible-pointed cappings have been
tested (CSIRO Report DTF505, February 1998 among others) at cyclonic
wind speeds of up to 74 metres per second without distress.
Under Australian Standard AS 2050 Fixing of Roof Tiles, traditional
sand-cement mortar bedding and pointing may not be used in high
wind areas - that is, above 33 metres per second - without additional
mechanical fixing such as clips or other fasteners. However flexible
pointing should be used in wind areas without additional mechanical
fixing.
Flexible pointing should be used in wind areas above 33 metres per
second, on steeply pitched roofs or those with difficult access,
for example multi-storey buildings. Although slightly more expensive,
the benefits are such that flexible pointing should be used on all
roof capping.
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Fixing Ridge Capping on a Steeply
Pitched Roof
Effective fixing of ridge capping is always essential but more so
on a steeply pitched roof because of the substantial forces at work.
As well, maintenance or repairs are more difficult, and therefore
more costly, than on a lower pitched roof, especially on buildings
of more than one storey.
What is steep? Generally it is defined as a pitch at or above 30
degrees. The traditional method for fixing ridge capping on a steeply-pitched
roof is to bed the capping in a standard cement mortar linked across
the ridge by reinforcing mesh held in a place by a hooked nail.
This works well but is laborious and therefore relatively costly.
An effective and economical alternative is to bed the ridge capping
using a flexible dry fixing strip. One such product widely use in
Victoria consists of a self-adhesive, extruded polyurethane strip
impregnated with water based emulsion. This product is available
in three shapes to match popular tile profiles.
Dry fixing replaces
the traditional mortar bed and has the advantage of being quick
and easy to apply.
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A flexible pointing material should be applied following dry fixing.
Flexible pointing also has greater adhesions - 20 to 30 times that of conventional bedding and pointing - as well
as the ability to absorb structural movement without cracking.
The result is an attractive, water-tight, durable ridge capping
that should not require maintenance or repair for many years. Initial
labour costs may also be reduced making this enhanced method of
fixing ridge capping on steep pitches both cost-effective and structurally
superior.
A range of dry fixing materials is available for other applications
including valleys and bird-proofing of eaves.
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This article sourced from the Victorian Roofing Tile Association Inc. |
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