'The durability and design life of the external face of the enclosure and its components should be related to, but not necessarily the same as, the design life of the completed building . . . The designer should, nevertheless, assess as precisely as possible the required minimum life of the enclosure as a whole (with maintenance considered),' states bs8200 Design of non-loadbearing external vertical enclosures of buildings.
It is not disputed that, for architectural applications, aluminium is the most durable of all the commonly used metals. Indeed, aluminium structures have an almost unlimited technical life - bs5427 states that 'mill finish aluminium will last the life of the building'.
It is a fact that modern alloys can give aluminium the same strength as steel, but with less than half the weight. Aluminium's performance in fire has led to its adoption for roofing by all the major supermarkets. Its scrap value is approximately 30 times greater than that of steel - and all in a material that can be infinitely recycled into new architectural products of the same quality, so meeting any and all likely end-of-life directives or other environmental legislation that may be issued by the European Parliament.
Less well known is that the surface of aluminium is ideally suited to receiving a wide range of different organic coatings, so producing a decorative material that will have a greater aesthetic life and lower maintenance costs than any comparative product. In fact, one of the major differences between coatings on aluminium and coatings on steel is that coatings on aluminium are there to decorate the substrate, not protect it. Aluminium is naturally so corrosion-resistant that it doesn't need to be protected - the coatings are there purely to provide a long aesthetic or decorative life - so fulfilling the vision of the architect who originally conceived the project.
Hoogovens buys its coated aluminium from Euramax Coated Products in Corby, which began its coil coating operation in 1983 and which operates the uk's only major aluminium coil coating line. Euramax has invested extensively in developing and testing products for architectural applications and has now supplied many millions of m2 of sheet and coil that have been fabricated into a multitude of different roofing and cladding products by customers in the uk, Scandinavia, Italy and the Middle East. Each of these environments places its own demands on the performance of the material, although high levels of uv (sunlight) combined with high humidity place the greatest strain on organic coatings.
There are three basic coating systems for architecture, all with an almost unlimited colour range, and all with full British Board of Agrement approval. These are:
Polyester - as used to clad caravans, this product is available in all gloss levels
ars - a polyester or polyurethane resin reinforced with nylon, giving outstanding uv and corrosion resistance and excellent resistance to mechanical damage during fabrication and construction.
PVdF - commonly known as pvf2, even after 30 years' use this still represents the state of the art in providing a long aesthetic life and is the coating of choice for all long-life projects, such as the new roof on Wimbledon Court Number One. Typically this product will give a service life without maintenance over painting in excess of 30 years. This compares very well with the 'decision to repaint' life expectancy of inferior cladding systems.
For particularly harsh or difficult environments, such as paper mills, leisure pools, large areas and areas not washed by rainfall such as soffits, we offer high-build primers, barrier coats or other modifications to systems, to ensure customers get the service and performance of their specifications. These may additionally be needed with specific metallic colours, or bright blue or yellow house colours to ensure stability of the pigments.
In service, aluminium roofs simply don't fail. As long as building guidelines are followed, the product will do exactly what the technical manuals say it will do. In fact, the only reported case of corrosion Euramax has received in its entire history was on a flat cladding where the tight bend radii on the cassette edges had caused a serious problem. Restrictions on bend radii apply equally well to steel products. An impressive record considering the amount of material produced each year. An important difference to steel is that where cut edges are exposed to the elements, aluminium's oxide layer prevents the kind of edge creep and corrosion that can lead to premature failure of the coating or substrate. What other material can make that claim?
Coated aluminium will not crack, craze or delaminate. In practice, the surface of the coating breaks down by slowly chalking. Chalking is the release of non-bound powdery pigment from the surface of the film. Even after chalking starts, apart from a loss of gloss, it will be many years before customers are aware that there is any change in the appearance of the building, as any change in appearance will be uniform along any elevation. Typical decorative lives for the coatings only are detailed in the table. The aluminium underneath will continue to perform long after the paint ceases to be decorative.
Historically, aluminium has been specified wherever clients have been responsible not only for the construction of a building but also for its maintenance and disposing of the materials when they come to the end of their useful life (watch out for ec legislation and 'End of Life Directives' that will be introduced shortly). Recent converts to aluminium have been attracted by the superior performance of the material as they become disillusioned by failures and the endless cycle of maintenance repair of inferior systems.
Guarantees on performance aren't much good when your own reputation is at risk. Customer confidence in individual architects and specifiers can quickly evaporate if products don't perform as required or if maintenance costs become a haemorrhage on customers' finances.
As far as coated aluminium cladding is concerned, although this a decorative product - which means that you have to look after it to keep it looking decorative - maintenance in practice is very minimal. Exposed areas are mainly kept clean by the natural beneficial washing action of rainfall. Areas not exposed to rainfall, such as soffits, may need regular cleaning to remove potentially corrosive deposits.
The uk has a well-organised secondary aluminum industry well able to cope with as much scrap aluminium as may be generated. At the end of its useful life, coated aluminum is efficiently converted back to new materials of the same quality - the remaining coating is burned off without affecting the product in way whatsoever. In fact, for the truly environmentally conscious a roof can be taken down, remelted into ingot, rolled to thickness, coated and profiled, so that in theory the same metal can be put back on to the same roof. What other materials can offer this level of conformity to the problem of waste disposal, especially when you consider that the price of the scrap is a significant part of the cost of the product initially purchased and that this is a inherent part of the value of the structure.
So as far as we are concerned, durability means the aesthetic life of the product in terms of the design life of the building, not the time it takes to look so horrible that the owner decides to paint over what was originally there. The list of failures for PvDF coatings on buildings in its 30-year history is hardly a list - nothing comes near this level of performance. The product is effective as a cladding or roofing solution from every aspect of design. It performs to customers' expectations. It is an environmentalist's dream - aluminum products and suppliers are mentioned positively in Greenpeace literature on construction. It is simply a product that does what it is supposed to do. In fact, on a recent visit to Hoogovens I was invited to look at an industrial estate in Warrington, a heavy industrial environment, where aluminium cladding in bright colours had been erected over 15 years ago. The photographs opposite show that this material is performing as well now as the day it was first installed. No wonder that architects worldwide specify PVdF on aluminium wherever they want their reputations to do what their creations do - stand the test of time.
David J Goddard
Sales and marketing director, Euramax