Natural Anodized Aluminium Cladding Panels have been around the architectural market for several decades now. The use of natural anodizing though in cladding panels have not been as widespread as natural anodizing in extrusion profiles. Though, it is indeed an excellent option to consider with.
We discuss with Dirk Verwimp, an expert in this field and currently Business Unit Manager for Almeco Group in Italy.
Skyline Facades: Dirk, what are the advantages of natural anodized cladding panels?
Dirk: There are actually several. To start with, the anodic layer is inherent to the aluminium substrate, so it will never peel, chip or chalk. Anodising for facade cladding is a durable and sustainable solution with an unlimited design lifetime. In case of replacing the panel, the material is very easy to recycle at a fraction of the energy to produce new aluminium.
The material is UV resistant and the metallic lusture and gloss will be maintained over time. Pre-anodised facade cladding is easy to maintain and is graffiti proof. And finally, it is a 100% pure aluminium product with an attractive aesthetic appearance.
Umeus Student Home, Copenhagen / Denmark
Skyline: There are pre-anodized cladding panels and post-anodized cladding panels. What are the actual differences?
Dirk: Selecting pre-anodising will enhance your cost efficiency as the material can be post transformed into any type of cladding. Further, due to the constant and automatic processing on coils, the material will have an excellent uniformity. After the process , the coils can be levelled and cut into stress free sheets, which avoids tension in the cassettes.
Post anodising is mostly selected in case of extruded profiles or for very complex structures. As the process is manual, it is very work intensive which is reflected in the cost. As one load contains no more than 20-30 m2, there is a risk of colour and gloss variation on your facade. With post anodising you can achieve higher anodic layers, as prescribed in the British Standards, but this is in fact not always an insurance for better quality. These high anodic layers are often forced which results in a soft top layer that can be reduced over time.
Ideally pre anodised material is used for large facade surfaces where uniformity is essential, with the combination of batch anodised extruded profiles for the trims or finishing parts.
Learown Fuda Square, Shenzhen, China
Skyline: What are the finishes that can be achieved with natural anodizing? As architects, or façade consultants, do we have a wide range to choose from?
Dirk: Generally anodising can be provided on different type of textures. Standard and well known in the market is the mill finish surface, which is a smooth and satin surface. But more and more different textures are requested by architects, where brushed, sand blasted and BRITE finishes or textures can be offered. The pre-treatment on these textures are different and usually the chemical etching part in the process is skipped in order to maintain as much as gloss or brushed definition as possible.
Besides the different textures, modern natural anodizing offers also a wide range of colours: natural, gold, bronze, copper and zinc. Each of these colours will look different on different textures. This allows the architect to maximise its creativity by combining the preferred textures with the preferred colour tone.
Bloom College, Wavrin / France
Skyline: Can you explain us briefly the production process for natural anodized cladding?
Dirk: The standard alloy for mill finish anodised aluminium is 5005 H14. The optimal anodic layer is 15 microns for exterior use, depending on the specification. We can offer also 20 and 25 microns on coil depending on the location of the project.
The process starts with a 3 step pre-treatment: degreasing for oil removal, etching for defining the right gloss and neutralisation to clean the smut and block the pH entering the acidic anodising tank.
After the anodising step, the material can be coloured, where pigments or metal salt is deposited into the porous structure of the anodic layer. Finally, the material is sealed in a hot water tank, closing the porous structure and fixing the colour. It is important to opt for a QUALANOD certified supplier which ensures the quality and processing according European norms and standards.
E-Sport Arena, Hangzhou / China
Skyline: Is anodized cracking, when bended, an issue?
Dirk: If you produce cassettes or other types of panels from pre-anodised aluminium, you will always have superficial hairlines perpendicular to the rolling mill directions. This superficial hairlines, also called crazing, is a natural effect and only visible under certain angels and light. This phenomena is purely aesthetical and will not affect the quality nor the warranty.
We always recommend to reduce the bending radius to a minimum (in accordance with the limits of the metal substrate) in order to minimise the area of the crazing.
Chang’An Cloud, China
Skyline: What is the actual lifetime of a natural anodized cladding panel and what are the factors that affect it?
Dirk: Natural anodized suppliers provide different warranties, for us 25 years of warranty is a standard, but in fact the design life is unlimited. The material is 100% pure aluminium and has a very strong resistance towards weathering. Factors that can influence the lifetime is direct contact with cement, acidic or alkaline substances which can attack the anodic layer. This must be avoided.