New British Standard for external rendering will change common practice

Publication in March 2005 of the European Standard for External Rendering has been long awaited and is a ‘must read’ document for those architects, specifiers and plastering contractors involved in external rendering.

At first glance, the 50 pages of eurospeak from the committee responsible, which took 5 years from its original draft to approve and publish, it might appear to the experienced plastering contractor not to contain too much that he does not already practice. For the less experienced contractor, there is a word of warning that he would do well to heed. This centres on the choice of beading available to him.

Specifiers will now have to be much more vigilant over the selection of beading used for external rendering, as the Standard signals alerts over the presence of salts in the atmosphere or background which could result in corrosion.

BS EN 13914-1: 2005 stipulates that specifiers and contractors have two main choices of beading. These are either PVCu or stainless steel. The use of galvanised steel is permitted, albeit heavily qualified with regard to the level of salts, which it does not attempt to quantify further. It would therefore be a brave decision to permit their use, as there is significant ‘wriggle room’ for the client when corrosion occurs. In any case, PVCu beads are the more cost effective option, as galvanised beads must now be hot dipped after manufacture, greatly increasing costs.

It has been common practice on the Continent to use dedicated external beads for many years and, more recently, most builders merchants in Ireland offer a PVCu option. The UK, however, has been slow to adapt to the reality that corrosion can and should be prevented. This will certainly change during the coming months, as building contractors will be obliged to ensure that rendering conforms to the new standard. The plastering trade well remembers when Tony Pidgley of Berkeley Homes went Back to the Floor on BBC2 and was staggered that the plastering contractor had used internal beads in a rendered column. These rusted even before handover.

Who bears responsibility to ensure that the new standard is applied? It was alarming when 200 architects’ practices were surveyed recently, that a high proportion left the choice of beading to the contractor. Many admitted to having had corrosion problems on their projects. Whether the architect or the contractor takes the initiative, it is plain that the client now has a potential claim if BS EN 13914-1 is not applied.

PVCu beads have been available in the UK for over 15 years and they are the most cost-effective bead to specify to conform to this new standard. Renderplas Ltd was formed in 1990 to design a range of beads guaranteed to prevent corrosion and PVCu was the natural choice of material. This had never before been utilised by a UK manufacturer and the prime task was to design beads suitable for the growing trend towards the use of through-coloured renders. So successful were they that now, every UK bead manufacturer has a PVCu option based on the Renderplas design, which has become generic.

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