22 RCI 0514

RCI May 2014

ISSUES & SOLUTIONS 022 MAY 2014 RCIMAG.COM Leave no stone unturned Agree? Disagree? Are there any issues on any aspect of the roofing, cladding or insulation sectors you would like to see discussed in future Issues & Solutions columns? If so, email the editor: mdowns@unity-media.com The issue Causing confusion for many, determining the quality of a slate can pose somewhat of a dilemma, particularly for specifiers who, due to conflicting information, are left unsure about what to consider when it comes to ensuring good quality slate is supplied. And because of this perceived complexity in choosing and specifying slate correctly, theories that wouldn’t wash in other industries are sometimes put forward as a way of taking advantage of this uncertainty – no one wants problems after all. An example of this would be some marketers claiming that slate from certain geographical locations being blanket superior to that from other origins. It’s simply not true. Any geologist worth his or her salt would remind you of the fact that slate is a natural product, and that the only true way of determining the quality of a piece of rock is by following the right procedures in terms of getting the relevant testing done and interpreting those results accordingly. And yes, if a quarry does already have a poor track record – or a certain seam of metamorphic rock pertaining to a few quarries has already been proven to be problematic – then caution is certainly the best option. Especially when the price appears to be particularly enticing. But such occurrences should not be used to tar the reputation of a whole region whether it’s Spain, North America, Wales or further afield. Because test results do not lie and if the economics of slate production mean that you can find an equally good slate elsewhere then the consumer should be able to benefit from this, rather than having to be cajoled into forking out more for what performance wise is effectively the same thing. Of course, other factors such as traceability (there is no point having results that do not relate to the product being purchased) and aesthetics (if you want a thicker, rougher looking, green slate instead of a smooth grey one, for example) do also come into play, however, if the overriding decision to select a certain slate is made with only origin in mind, then it is entirely possible that the best value won’t be achieved, and worse still, in some cases, slates that are not fit for purpose selected with potentially catastrophic consequences. The Solution To help overcome these issues, a greater level of awareness is required throughout the industry to help arm specifiers with the right knowledge to make the correct choices to provide the best solution to their problem. Addressing the main issue first and foremost is a good place to start – a specified geographical location from which the slate “should be” sourced is not a necessary (or sufficient) condition when it comes to ensuring quality. Due to the timescales involved in the formation of slate – many hundreds of millions of years, the bands of rock were crisscrossing one single landmass – the supercontinent known as Pangea. It is only as the continents have moved apart over time that slate can be found in different countries – in many cases, it is entirely possible to find ‘matching’ slates thousands of miles away from one another in different countries or even continents. What does matter, however, is the type of rock from which the slate is mined in various regions. In Spain, several different grades and types of slate can be found – the La Cabrera region for example, has what is considered to be some of the best grades of rock in the world. There are similar quarries in Argentina that boast rock from the Precambrian era which following thorough testing, have been found to achieve a water absorption rate of only 0.1%, which is perhaps one of the lowest water absorption rates achieved in slate testing history. This point is particularly important when it comes to determining the quality of slate as this indicates how porous the slate is – if the water absorption rate is too high then the slate will act like a sponge, taking in water, which will in turn make the slate much heavier. Worse, water contained within the slate will freeze in colder climes, then later thawing, weakening the slate. If this ‘freeze and thaw’ process occurs too often, the slate could crack or delaminate leading to its eventual removal from a roof. In order to minimise the level of poor quality slates being introduced into the market, a standard has been in use in France – the biggest consumer of natural slate products globally – to ensure that its slates meet the most exacting of requirements. This standard – NF 228 – tests for water absorption levels, flexural and transversal strengths, density and the carbonate and non carbonate content. This independent testing procedure ensures that NF certified slates will not rust or leach, and importantly will not fade over time. Whilst this standard is not obligatory within the UK market, taking it into account does help to ensure that any slates supplied are of a better quality since they will have been subjected to a more rigorous testing process. Whereas CE certification only states what results were achieved, the NF mark indicates that the slate has actually passed the criteria of a Pass / Fail test, helping to further ensure better quality slate in the process. As slate specialists at SSQ we recommend slates chosen that comply with the NF standard which – in addition to ensuring a greater quality of slate – also provides a much better level of traceability: Every pallet of NF 228 certified slate, for example, is stamped with the NF mark, meaning it can be thoroughly traced throughout the process. Whilst it should be noted that it is incredibly difficult to guarantee the absolute quality of every piece of slate, since many factors are involved – the more specialist the supplier, the more consistent the supply is likely to be. Being able to back this up with independent testing, such as that provided by the NF standard, provides further reassurance and ensures that beautiful slate roof will last for many, many years to come. www.ssq.com Haroun El-Helw of SSQ outlines the issues relating to determining the quality of a slate amidst all the “conflicting information” “If the overriding decision to select a certain slate is made with only origin in mind, then it is entirely possible that the best value won’t be achieved”


RCI May 2014
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