The wrong choice of beading for renders can result in costly claims and tarnished reputations, according to Kevin Leedham-Green, the managing director of the UK-based Renderplas Limited.

''Rendered finishes have been around since the introduction of Portland cement 180 years ago. They can provide a welcome alternative to the monotony of bricks,'' he says. ''Today's modern renders are self-coloured and can be scraped back to look like natural stone, but at a fraction of the cost. Maintenance free, apart from an occasional washdown in polluted urban areas, rendered finishes provide excellent protection against the elements and can add colour, texture and design flair to the environment.''

''With all this going for it, why do specifiers and site agents permit contractors to install galvanised beads with the risk of compromising the whole project?'' Leedham-Green asks.

''The possible consequences are that, within a short period, rust stains will start to leach through and corrosion will ultimately cause the render to spall,'' he explains. ''The problem is likely to be more acute in the Gulf which has a more aggressive climate.''

''The problem was recently highlighted on television nationally in the UK on Back to the Wall, when the CEO of a wellknown housebuilder found that beads had rusted in newly-rendered pillars, even before the building was handed over. We never learned whether this was caused through casual specifying, inadequate site management or cowboy subcontracting. The remedy of chopping out and rerendering is costly and seldom satisfactory.

''It is also totally avoidable, providing the specification is properly defined in the plans and followed through on site. BS5262:1991 and BS8000:part 10, currently applicable for rendering, were in some respects outdated even before publication. Continental practice in this respect is much stricter. The UK submission for the draft European standard prEN 139141 on rendering specifies that stainless steel or PVC beads should be used but that unprotected galvanised beads have no place in external situations.''

He continues: ''Does this mean that higher standards will lead to increased costs? This is not necessarily the case, particularly if the PVC option is chosen. PVC is the most economical external bead available on the market. Already the first choice for most render manufacturers, they not only offer a guarantee against corrosion, but are more suited to the modern scraped finishes due to their finer arris. Beads can also be supplied in a compatible shade to match the colour of the render, making them blend in harmoniously.

''PVC beads first appeared in America more than 60 years ago and are produced by the largest bead manufacturer in the world, where they enjoy a close to 50 per cent share with metal beads.''

It is up to architects to recognise the corrosion dangers and avoid unnecessary claims and tarnished reputations, he concludes.

Renderplas was formed in 1990 to design a range of plasterers' beads produced in uPVC. The company's website (www.renderplas.co.uk) offers specifiers further details and allows them to input the drawings directly using AutoCad.

Renderplas is represented in the region by Materials Trading in Dubai, UAE.