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.
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.
Fixing Ridge Capping on a SteeplyPitched 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.
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.