Last edited 26 Nov 2020

Coating

[edit] Introduction

In the construction industry, a coating is a protective layer applied to the surface of a material (the substrate) to:

Provide protection from some deleterious or unwanted effect, whether from rainwater, condensation, corrosive substances, (e.g zinc coating on iron, steel or other metal - called galvanising which provides a sacrificial zinc coating that protects the substrate from oxidation and corrosion.)
To improve performance. For example, the properties of plain glass may be enhanced by a range of coatings which can improve its performance and aesthetic qualities, e.g reduce heat loss, minimise solar gain, apply a mirrored effect etc.
Provide a decorative effect e.g paint (which also protects the substrate).
Provide fire protection. Intumescent paint can be brushed or sprayed on and provides fire protection for a limited period. It works by swelling up when exposed to heat, increasing in volume and decreasing in density. The resulting ‘char’ retards the spread of flame due to its poor heat conductivity. Intumescent paints are used for passive fire applications such as fire -proofing structural steel.
Seal a substrate e.g tensile fabrics, normally coated on both sides. If a fabric is to be used externally for a tensile structure, it is usually coated either with PVC or PTFE (Teflon) and can last in excess of 20 years. In some cases this may be further protected by a durable topcoat.

In most cases, coatings are very thin, sometimes just microns thick, depending on how they are applied:

Brush, e.g anti-rust paints and graffiti-resistant wall paints.
Spray e.g lacquers which can be applied to furniture to both protect and enhance.
Heat-cured e.g powder coating (sometimes called polyester powder coating (PPC)) which comprises polymer or thermoplastic powder that is heat cured to produce a coating of uniform thickness. The result is a very tough coating which does not suffer the unevenness, drips, runs and emissions of volatile organic compounds (VOC) normally associated with paints and sprays. Powder coating is typically used on aluminium profiles, household appliances and more recently, medium-density fibre-board (MDF). ‘Powder-coated’ aluminium door, window and structural profiles have become very common in the construction industry providing a full range of colours to harmonise with most designs.