(a) Primers pigmented with metallic elements anodic to steel For primers applied directly to steel surfaces, these are also usually required to provide corrosion inhibition. Its purpose is to wet the surface and to provide good adhesion for subsequently applied coats. The primer is applied directly onto the cleaned steel surface or, in the case of duplex systems, the sealed metal coating. Paints are usually applied one coat on top of another and each coat has a specific function / purpose. Intermediate and finish coats are usually classified according to their binders, e.g. Each of these inhibitive pigments can be incorporated into a range of binder resins giving for example, zinc phosphate alkyd primers, zinc phosphate epoxy primers, etc. zinc phosphate primers and metallic zinc primers, etc. Primers for steel are usually classified according to the main corrosion inhibitive pigments used in their formulation, e.g. The most common methods of classifying paints are either by their pigmentation or by their binder type. Since, in the broadest terms, a paint consists of a particular pigment, dispersed in a particular binder, dissolved in a particular solvent then the number of generic types of paint is limited. In general the corrosion protection afforded by a paint film is directly proportional to its dry film thickness. dft = 'wet film' thickness multiplied by the % vol. The relationship between the applied 'wet film' thickness and the final 'dry film' thicknesses (dft) is determined by the percentage volume solids of the paint, i.e. The thickness of the 'dry film' can be measured, usually with an electro-magnetic induction gauge. As the solvent evaporates, film formation occurs, leaving the binder and pigments on the surface as a 'dry film'. 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.

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