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Surface Finishing

There are many surface finishing options available such as anodising, powdercoat, PVF2, galvanising and industrial paint - it is therefore important to specify the best solution for your project's construction methodology and environmental exposure. 

In spite of the fact that aluminium self passivates (surface oxidation), surface coatings allow for the metal to have greater resistance, thereby increasing durability, whilst also allowing colours and special effects to be added to the metal itself.

Stainless steel and weathering steel (Corten) also both self passivate but have completely different surface finishes based on their alloy compositions - but neither of these finishes require surface coating to extend their life expectencies.

Cast, rolled, plate etc or other mill finished steel sections do however require additional surface finishes - when used externally or structurally, they must be suitably industrial paint coated (often a multiple layered process) or galvanised to meet the structural integrity of 50 years.

The most common methods of protecting and adding colour to metal are the following:

  • Powdercoating - Aluminium or Steel 

  • PVF2 (Polyvinyl flouride)

  • Anodising - Aluminium

  • Galvanising - Steel  

  • Industrial Painting systems - Steel 

Powdercoating
Powdercoating is without doubt one of the most common methods of protecting aluminum in the building industry due to the large range of colours and the durability of the harder and often tougher surface powdercoating than can be achieved with conventional liquid paints.

Powdercoating is the process of adding a coloured powder electrostatically to a negatively charged piece of metal and then cured under heat to allow the coating to flow and form a coating or skin.

Advantages of powdercoating are:

  • Emits zero VOC (volatile organic compounds).

  • Can produce much thicker coatings than liquid paints - without the paint system running.

  • Overspray can be recycled.

  • Colour consistency between batches is maintained.

  • Many specialty colours and effects can be achieved - including 'look-a-like' anodised.

  • Small scratches can be repaired with an approved touch-up paint from the paint supplier.

  • Warranties available up to 20 years (for film and colour).

Thermosash recommend a polyester powdercoat -  which is available in various performance levels depending on the severity of the environment  and warranty being sought for the project. Both standard and special colours available.

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PVF2  - Flourocarbon finishes 
Available on request this special finish type has excellent resistance to weathering and staining and can have extremely long surface colour-fastness.

The finish has been noted to last upwards of 70 years if maintained in accordance with manufacturer's instructions.

Warranties are generally for 10 years.

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Anodised 
Anodising is the process of electrolytic passivation - used to increase the thickness of the natural oxide layer in aluminium and provide a colour by dyeing. The process increases the corrosion and wear resistance - the greater the thickness the greater the resistance.

The advatages of anodised as a surface finish are:

  • Superior bonding of the colour - as it is a metal reaction rather than a coating.

  • Colour stability.

  • A safe coating process that is non hazardous, not harmful to human health nor has any dangerous by-products.

Whilst dissadavantages of the finish can be:

  • Brittleness of the coating and susceptability to scratching if care is not undertaken during manufacture or on-site . 

  • Scratches can be difficult to repair.

  • Due to the coating process being critical to time - batches can vary in shades.

Thermosash recommend commercial grade 20 micron finish for exterior building applications.

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Galvanising
This process in the commerical window trade is limited generally to structural elements that are not visible. The protective finish is achieved by either hot dipping or electroplating of the steel or iron with zinc. Hot dipping produces a duller grey finish whilst the electroplating appears as a brighter silver coating. The zinc acts as a sacrificial anode to the metal it coats - and even if the coating is scratched  the exposed steel will, under most conditions, remain protected from the remaining zinc.

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Advantages:

  • Low cost.

  • Under most service conditions - long maintenance free service life.

  • Durable.

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Industrial Painting
Steel or iron, when used in exposed or potentially humid or wet environments, require surface protection. When the steel has an aesthetic application it is common for the steel to be painted rather than galvanised. 

When the steel element is exposed or a critical structural element, an assessment should be made on the weathering ability of the steel over the life of the project and whether maintenance will be easy to undertake. 

It is recommended that the paint specification is undertaken specifically for the project and monitored by a recognised industrial paint representative.

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