Plan early for the finish

Richard Besant is Sales Director at Powdertech (Corby) Ltd, the architectural metal finishing company. Powdertech was established in 1988 and is a leading industry supplier. Over the next few months Richard will share his views on current metal finishing issues.

“In this article I would like to explain why the exterior finish to a building merits early planning, why coatings need to be tightly specified and why metal fabrications need to be designed in such a way as to optimise the metal finishing process.

The exterior envelope to a building expresses the character and values of the company and occupants of that building. It makes an immediate impression on viewers, visitors and users. Is it smart and well maintained? Is it colourful and fun, or subtle and sophisticated? Is it breaking boundaries and trying something new and radical? Given the importance of this first impression it often baffles me that the question of final coating is not given full consideration at the start of a project. By ‘full consideration’ I mean detailed specifications for the metal finishing process, and designing external fabrications with the metal finishing process in mind.

So why is a rigorous specification so important? A uniform finish, in terms of colour, gloss level and crucially, durability, is critical to the overall success of the building’s final appearance. Terms such as ‘equal or equivalent to’ are often used in the specification notes for metal coatings but this is simply inadequate. After strictly defining the majority of components it seems that providing full details for the finish is too much of a stretch! With a vague starting point, problems begin to mount up as the construction process is moved along the supply chain. Since the building envelope is rarely made by a single contractor, elements from various subcontractors end up at a variety of metal finishers, all using different pre-treatment methods and different makes of paint or powder. The interpretation of ‘equal or equivalent to’ by different metal finishers results in a building that fails to achieve uniformity in colour and longevity of finish. When small elements such as cills and flashings are finished to a lower quality they can begin to peel and corrode within five years and the building will begin to look unsightly and need maintenance even if the main cladding has a life span of twenty five years.

Loose specifications can also result in misinterpretation and confusion. Order forms received at Powdertech have been known to disagree entirely with the original drawing annotations. Time is then wasted going back up the supply chain to determine the original architect’s or designer’s intent for the finish.

Attention to simple yet essential elements in the metal fabrication design will ensure that maximum benefit is derived from the final coating. There are a number of well-tested rules that need to be observed. All external metals elements should be designed to eliminate water traps and allow run-off. Overlapping joints, or other materials in contact with the metal should be avoided as these may induce capillary action which pulls water underneath the sheet of metal and could lead to corrosion. Sharp edges must be rounded off to prevent the coating fracturing or thinning in these areas. Deep recesses in a metal fabrication should be avoided as the ‘Faraday cage effect’ can prevent the electrostatically charged powder from coating that area. Ideally a recess should not be deeper than it is wide. Suitable jigging points need to be incorporated into the design in order for the piece of metal to be suspended during the powder coating process.

For galvanizing, ventilation and drainage holes need to be drilled into hollow objects. These should be in particular places and of a specific size so that the object will sink, and excess zinc drain away once it is removed from the tank. External stiffeners at the corners of objects need to be cropped to allow a continuous flow of zinc and avoid dead pockets of air and ash.

Incorporating these simple design elements before material arrives at the metal finisher will avoid time delays in addressing problems and will result in an optimum finish across the metal surface.

I hope that in this brief overview I have demonstrated that spending time on strict specification and design to improve the metal finishing process are extremely important steps in the construction process. Allocating time and attention, early on, for the very final part of construction – the exterior finish – will ensure that the completed building will do justice both to the original design vision and to the time and money spent on achieving it.”

Contact: richard.b(Replace this parenthesis with the @ sign)