5 Things About Rainscreen Cladding Finishes You Need to Know

26th March 2021

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The decision of what colour or finish you want for your building is a tricky one, and not one that is ever taken lightly. Architects go to a lot of effort to research the surrounding area to find out what influential buildings are already there. What is the heritage of the local area? Is there any old heritage or industry that we should reflect in our facade?

Once the rough colour palette of materials has been decided, the tricky decision process as to what specific colour, texture, gloss level and finish begin… is tricky because it needs to be right! A high gloss level in the wrong place can ruin the appearance of a building. Colour variation in the wrong place can look awful. So, as I say, it needs to be right.  A bright and vivid colour in the wrong place could be enough to put someone off buying a building. The large majority of external rainscreen cladding panels on buildings are aluminium. Aluminium finishes fall into two main categories: Polyester powder Coated (PPC) and Anodised.

To assist you in your decision as to which way to go, here’s a few things you need to know:

1.) Anodising is not a coating. Anodising is a process where a very thin top surface of the aluminium is etched away, opening up the pores of the aluminium material. Then through an electrolysis process, an anodised film is formed on the surface of the metal. The anodic film is impregnated into the metal itself rather than a coating on the outside.

2.) Natural Silver anodising (also known as natural anodising or satin anodising) is not a colour.  The process described above does not involve any colour at all. The result of natural silver anodising is that the natural colour of aluminium is what you can see. The natural grain in the aluminium is generally not visible as this is removed in the etching process. To create colour, dyes are added during the process which creates bronze and other colours. Different grades of aluminium will create different gloss levels.

3.) Colour consistency cannot be guaranteed with any anodised finish.  As this is a natural process, working with natural raw materials, and created through a manual process, there will be variance in the final finish. This can be controlled by procuring material from the same coil and batch anodising at the same time, and using good, experienced anodises. However, there will be some variance so you must appreciate this. Some architects choose anodised finishes for this very reason as it gives a more natural feel to the building.

4.) You can’t use the same grade of aluminium for anodising and powder coating.  If you decide on a powder-coated finish, the base material will likely be a 1050 grade aluminium, however, if you tried to anodise this grade of aluminium it would come out with unusual streaks and inconstant colour across a panel, this is because the grade of aluminium isn’t suitable for anodising. If you opt for an anodised finish then a better grade of metal is required (and yes, more expensive). This will generally be a 55HX grade aluminium from Aleris or J57UP from Novelis.

5.) There are over 200 polyester powder-coated finishes.  Every RAL colour can be powder coated, and for each RAL colour, there are generally 3 different gloss levels: satin, matt, gloss. Then for some colours, there are different textures and metallic finishes. Four PPC ranges that are worthy of note in their own right: ANODIC POWDERS The Anodic PPC range has been developed to sit in-between standard flat powder coating and anodising. They have a metallic fleck in them and are supposed to mimic an anodised finish. As it is a coating you won’t get the colour variation as you would with an anodised finish, but rather a consistent colour. Akzo Nobel have a particularly good range of Anodic Finishes.

Textured Powders

Textured powders are applied like any other powder, but the difference with them is that the raw powder hasn’t been ground so finely, so when it is applied it creates small ‘lumps’ in the finish. This makes for an interesting appearance. Textured powders are generally ‘super matt’ in their appearance, meaning they have virtually zero gloss level.

Imitation Powders

Relatively new to the market has been the introduction of powder-coated finishes made to look like other metals, such as weathered steel, weathered copper, weathered zinc, GRC, and various other patina finishes. These are often created using different colour powders and flecks mixed or through two-pass powder coating using light water spray to separate different colours. The company leading the way in this field is a Spanish powder manufacturer Adapta Powder Coatings.

Bespoke Powders

The beauty of powder coating is whilst the existing range of powders listed above is almost endless, there is the odd occasion when a client wants something very specific or wants to match another product (a piece of furniture for example), and it simply doesn’t fit within any colour on the market. Or they want a particular RAL colour, but in a texture that isn’t currently available. Akzo Nobel, a leading powder manufacturer, offer a service where they can match textures and tones in their laboratory, and generally create an exact match.