THE INADEQUACY of the British Standard for stone cladding systems has led the sector's leading research body to issue its own guidance.
The publication of the Centre for Window & Cladding Technology's Guide to the selection and testing of stone panels for external use comes a week after a warning that engineers have overlooked durability problems in stone cladding and, following a recent court case, may be liable for failures (NCE 22 January).
The CWCT's guide was prepared by a 14 strong panel of engineers, manufacturers and architects. The foreword declares: 'At present the stone industry and specifiers appear to be in some confusion as to the necessity of stone testing and selection of tests for fitness of purpose'.
While declaring that BS 8298 is adequate for some straight-forward cladding systems, it concludes: 'It is for larger panels, or where durability of the stone is questionable because of adverse environmental conditions or lack of available data, that...the British Standard only gives limited guidance on the testing regime.'
The guide warns that many types of 'exotic' stone used in cladding systems may have 'no record of adequate performance in service in environmental conditions of the UK' and will therefore need to be subjected to a stringent testing regime.
The CWCT is also due to publish two other related documents, Standard for ventilated rainscreens and Fixings for natural stone. In parallel it is developing a database of natural stone for use in curtain walling which will draw together existing test results and contain information on the physical properties of stone commonly used in the UK for curtain walling.
The CWCT can be contacted on 01225 826541.