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Building Products January 2018

SSQ | COVER STORY JANUARY 2018 | BUILDING PRODUCTS 7 added scrutiny when it came to testing standards. Unfortunately though, it is generally agreed that the revision has resulted in further confusion, firmly placing the burden on the end user to select a slate. For example, the water absorption criterion has been somewhat convoluted. The water absorption test’s purpose is to quantify the percentage of water that a slate absorbs after it is submerged for a prolonged period. There is a direct correlation between slate’s absorption level and its susceptibility to damage in freeze/thaw cycles. This means that a slate with a relatively high absorption level is more likely to suffer a significantly lessened service life. Previously, to attain the highest award, slate would have had to adhere to a threshold figure of <0.6%. For many, this figure was already too high a limit. The preceding British standard set the bar at 0.3% and the French standard is 0.4%. Under current regulations, a slate that tests >0.6% can still carry the highest classification as long as it exhibits an adequate freeze-thaw resistance’ - a rather ambiguous classification. However, the most pressing issue surrounding the European standard continues to be the omission of a pass/fail criterion, which was present in previous European standards’ incarnations. Consequently, test results need to undergo timely and forensic analysis by specifiers to determine whether a slate is of the required quality. For example, the thermal cycle test is designed to determine the levels of rust or oxidization present in a slate. The samples are examined for corrosion and given a T1, T2 or T3 score, with T1 being the best quality category. This means, theoretically, a slate could achieve the lowest score in the thermal cycle criteria, and have a water absorption level of 0.6% and still claim compliance with the EN 12326 standard. Slate of this composition would be prone to appearance changes, which penetrate the slate and risk the formation of holes and would be at risk of critical failure due to cracking, increased weathering and damage caused by freeze-thaw cycles. SSQ recommends the use of slate and phyllites with water absorption lower than 0.4% (within the W1 threshold), as well as a T1 and S1 classification. For more information on how to interpret the BS EN 12326 and ensure a correct slate specification, please visit: www.ssqgroup.com Haroun El-Helw is Head of Marketing at SSQ Slate


Building Products January 2018
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