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An Introduction to Roofing Slate Prepared with the assistance of Dr. I. Sims, PhD, CGeol, Stats Consultancy.

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Presentation on theme: "An Introduction to Roofing Slate Prepared with the assistance of Dr. I. Sims, PhD, CGeol, Stats Consultancy."— Presentation transcript:

1 An Introduction to Roofing Slate Prepared with the assistance of Dr. I. Sims, PhD, CGeol, Stats Consultancy

2 Who are SSQ?  Founded in 1983  Producers and exporters of natural slate from Spain, Argentina and Brazil  Specialists in finest quality imported slate  Market leader in UK; exports to Europe and worldwide

3 Objectives  To explain the geological background of roofing slates  To demonstrate why natural slate makes such good roofing material  To explain the new European Standard for roofing slates  To provide advice on problem free slate specification

4 Contents  Introduction to slate – geology, extraction and source  Performance issues  The new European Standard & Quality Control  Problem-Free Specification  Conclusion

5 An introduction to slate  Definition ‘A smooth fine grained metamorphic rock which can be split into layers.’  History  Used since Roman times in Europe  Used for roofing in the UK for over 1000 years

6 Natural Slate is a fine-grained metamorphic rock, formed from the compressive pressure from both the sea and the earth’s core. Slate Layer The Formation of Natural Slate

7 Geology Mud on ocean bed 500 M yrs 300 M yrs 200 M yrs 2.5 M yrs Today Cambrian Ordovician Devonian Marine life Reptiles Dinosaurs Homo- Sapiens Hersynian Movements (volcanoes, earthquakes, and rising of mountains)

8 Mineralogical Composition  Main Components:  Chlorite  Quartz  Mica (including muscovite)  Additions  Feldspar  Carbonates (e.g. calcite & dolomite)  Opaques (e.g. pyrites, graphite)

9 Geology


11 Extraction Slate extracted around quartz vein Quarry rock face

12 Slate Production  SSQ Slate Production Video

13 Sources of Slate Used in UK

14 Performance Issues

15 Advantages of Natural Slates for Roofing  Durable  Waterproof  Minimum maintenance  Non combustible  Not susceptible to acid attack thus pollution resistant  Flexible  Natural product  Life cycle cost

16 Properties of a Good Roofing slate Suitability to climatic conditions:  Resistant to frost  Resistant to repeated wetting and drying Suitability for use on a roof:  Flatness  Regular thickness  Square cut  Longitudinal grain

17 Possible Visible Defects of Roofing slates  Non flatness  Irregularity in thickness  Cracks  Transversal grain  Non squareness  Flaking  Delamination

18 Twisted Defective Slate Cracks Different thickness Steps

19 Possible Invisible Defects in a roofing slate  Inclusions such as oxidising pyrite  Water absorption too high  Non resistance to acid attack  Non resistance to freeze-thaw cycles  Inclusions  Brittleness/breaking strength too low  Pre-existing delamination  Calcium carbonate content too high

20 Defective Slate: Pyrite Leaching Leaching and curved slates

21 Testing and Standards

22 International Standards  Until recently there were a number of international testing standards, with varying degrees of complexity:  In May 2006 the new BS European Standard (BS EN 12326) was introduced to supersede all other European national standards

23 BS EN12326 – Sample Test Certificate  CE Mark

24 BS EN12326 – CE Marking  You can check that slates are tested to the BS EN by looking for the CE marking on packaging and or any documentation accompanying the slates.  UK building regulations have been modified to ensure that only CE marked roofing products are used.  The CE mark is the manufacturers claim that the slate, has been tested to BS EN 12326

25  If the CE mark is not found, then the slates should be rejected. BS EN12326 – CE Marking

26  CE Marking does not indicate the Quality of the slate  The CE mark means the slate has been tested in the correct way

27  The performance of a slate is measured by various tests, with the most important being:  Dimensional tolerances (deviation from declared length, width, squareness and straightness)  Thickness  Resistance to flexion  Permeability - Water absorption  Durability  Freeze thaw  Thermal cycle test  Carbonate content  Sulfur dioxide exposure tests  Non-carbonate carbon content  External fire exposure  Release of dangerous substances European Standard BS EN 12326

28  No pass/fail criteria, instead has levels of performance for some tests and values for others  Any tested roofing slate can state compliance with the standard, and show the CE mark no matter what the quality is.  What constitutes a quality slate ? European Standard BS EN 12326

29  Non-visible: Test Certificate – What to Look For  Visible: Dimensional and thickness variations Flexural Well performing slates will have : longitudinal Flexural Resistance In excess of 65 MPa STRENGTH

30 Test Certificate – What to Look For Water Absorption, Permeability & Durability Quality slates have low water absorption Low risk of freeze-thaw damage British standard was <0.3% New standard: A1 = 0.6% Carbonate Content Differing types of carbonate have different potential for reaction Safe to assume slates with lower carbonate content will weather more slowly unless iron-sulphurs are present Proven quality roofing slates have carbonate content <3%

31 Test Certificate – What to Look For Thermal Cycling / Free of Oxidation Oxidation will occur if reactive iron-sulphur minerals are present (pyrites) Three Classifications: T1 free of pyrites or of leaching pyrites. Applied to slates that exhibit colour changes that neither affect the structure of the slate nor form runs of discolouration T2 exhibit pyrites/ leaching pyrites. Applied to slates that form runs of discolouration, but no structural changes T3 exhibit pyrites/ leaching/oxidising pyrites. Applied to slates that form runs of discolouration and may form holes around inclusions but no structural changes. Well performing slates will have no visible pyrites and be T1

32 Quick Quality Checklist What to Look For: Strength  Flexural Strength > 65 MPa Water Absorption  Water absorption < 0.3%, generally the lower the better (A1) Free of Oxidation  Avoid slates with potential for oxidation (T1) Carbonate Content  Carbonate content < 3%, generally the lower the better Proof  Proven history of performance in UK environment

33 Each label has the test data included Quick Quality Checklist What to Look For: CE Mark

34 Quick Quality Checklist What to Look For: Low Oxidation T1 Strength MOR > 65 MPa Water Absorption < 0.3% Low Carbonate content < 3%

35 Specification

36 A Check-List To Ensure Problem-Free Slate Specification Key Points:  Know the origin of the slate  Reliability of the importer  Check for CE Mark  Ask for recent BS EN test certificate showing date, name and origin of slate  Ask about quality control at source  Are sufficient stocks available?  Service and assistance of supplier  Written guarantee based on UK law  Ask for reference sites

37 Specifying Slate  Contractual specifications for roofing slates will need to be more sophisticated than in the past  No ‘blanket’ specifications  Ensure CE Marked Slates only  To ensure performance for at least 30 years, request slates with:  > 65 MoR, A1, and T1 results  Slates with < 65 MoR, A2, and T3 May comply but may last only a few years on a roof subjected to UK climactic conditions

38 Design Possibilities with Slate

39 Quality Imported Slates in UK  Spanish & Argentinean slates are used on listed buildings  Approved in Snowdonia National Park  Accepted by English Heritage  Some accepted by Historic Scotland

40 Applications of Quality Spanish Slate - Scotland Slate specially produced for Scottish market:  equivalent in colour  equivalent in texture and size  equivalent in performance to indigenous slate

41  Check for the CE Mark on labels & Certificates  Although the slate may be compliant with the new BS EN 12326 ensure it passes the Quick Quality Checklist Conclusion  Natural slate is the perfect roofing material  Natural slate is a low life cycle cost, low maintenance, environmentally friendly material  Slates may have defects not visible to the naked eye

42  Visit our website

43 An Introduction to Roofing Slate Any Questions?


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