The thickness of the 'wet film' can be measured, before the solvent evaporates, using a comb-gauge. Paints are applied to steel surfaces by many methods but in all cases this produces a 'wet film'. Solvents are usually organic liquids or water. Solvents are used to dissolve the binder and to facilitate application at the paint. The binder is the film forming component in the paint. Pigments are finely ground inorganic or organic powders which provide colour, opacity, film cohesion and sometimes corrosion inhibition.īinders are usually resins or oils but can be inorganic compounds such as soluble silicates. Paints are made by mixing and blending three main components: Composition of paints and film formation

6.3 Coating applicator training and certification (ICATS).

4 Main generic types of paint and their properties.

1 Composition of paints and film formation.

Each coating ‘layer’ in any protective system has a specific function, and the different types are applied in a particular sequence of primer followed by intermediate / build coats in the shop, and finally the finish or top coat either in the shop or on site. The protective paint systems usually consist of primer, undercoat(s) and finish coats. Modern specifications usually comprise a sequential coating application of paints or alternatively paints applied over metal coatings to form a ‘duplex’ coating system.

Examples of this are epoxy and polyester glass flake coatings that are designed for high build thickness in one or two coat applications, and single coat high build elastomeric urethane coatings, up to 1000μm thick. Previous five and six coat systems have been replaced by typically three coat alternatives, and the latest formulations have focussed on application in even fewer numbers of coats, but with increasing individual film thickness.

Paint systems for steel structures have developed over the years to comply with industrial environmental legislation and in response to demands from bridge and building owners for improved durability performance. Paint is the most commonly used material to protect steel.

Paint 2 coats