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Welsh
Natural Roofing Slates |
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| A range of natural slate roofing extracted
from quarries in North Wales |
| General |
Introduction
Slate is one of the oldest, most efficient and most attractive
roofing materials. The natural slate marketed by Welsh Slate is among
the highest quality slates available in Britain. It is extracted from
slate beds up to 950 million years old at quarries in North Wales
and the USA. |
Authority
The slates exceeds the standards stipulated by BS 680: Part1: 1944,
Part 2: 1971 Specification for roofing slates. The company is quality
assured to BS EN ISO 9001: 2000. The Penrhyn quarry is accredited
to ISO 14001: Environmental Management System. |
Applications
Natural slates may be used on roofs of over 20° pitch on all types
of building. They are particularly suitable for use on historic properties,
in conservation areas and on prestigious buildings. |
| Description |
| Slate is formed from the metamorphism of a sedimentary
shale which may contain clay, quartz and mica with smaller amounts
of iron, calcium and magnesium minerals, feldspars, pyrites and silicates.
When subjected to intense pressure, these minerals reorientate to
assume parallel positions perpendicular to the compressive forces.
This process produces the familiar slatey cleavage. |
Composition, manufacture
The slate is quarried by open cast mining techniques. The selected
raw material is then cut using diamond saws into smaller blocks and
the best material split using a light hammer and chisel into thin
sheets. These are dressed using a rotating cutting blade which puts
the characteristic chamfer on the face of the slates. |
| As roofing slates are produced from a natural material,
each individual hand made slate will have its own visual characteristics. |
Shape
Standard slates are rectangular with special shapes to individual
requirements. |
Density
Varies according to slate type, between 2,700 kg/m3 - 2,800 kg/m3. |
Appearance
Riven texture, rectangular with chamfered edges. Available in the
following 8 colours: Heather Blue, Heather Red, Heather Grey, Blue
Grey, Dark Blue Grey, Autumn Green, Vermont Green and Truthville Red. |
| Performance |
Liquids
Water absorption is less than 0.28% (minimum requirement
of BS 680 is 0.3%). Unaffected after 15 minutes wetting and drying
cycles (minimum BS 680 requirement). |
Chemical resistance
Unaffected after 10 days in 20% sulphuric acid solution and resistant
to alkalis and other chemicals. Slates are resistant to sever atmospheric
pollution, acid rain, sea air and salt spray. ASTM Class S1 (service
period of 75-100 years). |
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| Performance contd. |
Biological
Unaffected by moss and lichen growth, rot or by insect attack. |
Light
Unfading and unaffected by UV light. |
Compatibility
Compatible with other building materials. |
| Design Considerations |
| The company recommends its earliest involvement on
any roofing project and reference to BS 5534: Part 1: 1997 Code of
Practice for slating and tiling: design. |
| Sitework |
| The Approved Roofing Contractor scheme aims to ensure
that slates are fixed in accordance with BS 5534: Part 1: 1997 Code
of practice for slating and tiling and BS 8000: Part 6: 1990 Workmanship
on Building Sites. |
Handling
Slates should be stored on edge and stacked with battens between layers.
As slates may have sharp edges and can splinter, the use of a sturdy
pair of gloves is recommended. Any excessive inhalation of dust may
proved harmful and should be avoided. It is also advisable to wear
suitable eye protection to BS 9092 grade 2 (current COSHH data sheet
is available from the company). |
Sorting
It is important that slates are sorted into at least 3 grades whilst
holing, to ensure that the slates on any one course are of the same
thickness and to prevent ‘kicking’ slates and unsightly
gaps between courses. |
Holing
Slates should always be holed using a drilling or boring method from
the underside and positioned so that the thinner end is at the top
when fixed. |
Cutting
Slates should not be cut too narrow as this normally reduce the side
lap and, therefore, the integrity of the roof. The company recommends
the use of ‘slate and a halves’ at the end of alternate
courses and in cases where cutting normal slates would result in the
width being narrower than 150mm. |
Fixing
The roof should be properly marked out prior to any slates being fixed
and all slating work should be in accordance with the latest editions
of BS 5534 and BS8000: Part 6. Proper grading and selection of slates
is important to achieve a neat and attractive finish. Natural slate
should be considered as an individual unit and one slate may suit
a particular location on the roof better than another for reasons
of thickness, natural curvature, surface texture or appearance. |
| Supply |
Availability
Either direct from the company or through a network of distributors
whose names may be obtained from the company. |
| Services |
Sales and technical
Detailed technical advice, including roof specification and cost estimation
via a computer-based system and a free sample service is available.
A list of approved roofing contractors for the UK is also available. |
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