Coating Systems-Single & Multiple Coating Systems
Coating materials are components of coating systems. A coating system is comprised of the surface preparation method used, application equipment and processes and materials used for one or more layers of coating
Single Coating Systems
For many years, the main premise was that a single coat coating system was not sufficient to protect an industrial structure. However, with new technologies, advances in application equipment, and craft worker training, it is now possible to have a single coat coating system for certain applications. Solvent-free polyurethanes and epoxies are now being used in the mainstream business of corrosion protection. Tank linings, both in the marine industry and in the water and wastewater business, are using these single coat systems. Some manufacturers are pushing for use in other areas. A single coat system requires careful application of the coating and prompt detection of holidays or other defects. Specialized equipment is necessary and planning the coating application for ease of access is also very necessary.
Multiple Coating Systems
In most cases, a multiple-coat system is used in industrial and marine coating work. There are numerous reasons to use a multiple coating system. In many cases certain materials do an excellent job in one aspect of corrosion protection but not so well in other areas. The most common system uses an inorganic zinc as the primer, mainly because of its excellent adhesion to steel and its ability to provide cathodic protection at cuts, thus reducing the likelihood of undercutting corrosion. The second coat is normally a high-build epoxy, used as a barrier coat to reduce moisture penetration to the substrate. The final coat in an exterior system is typically polyurethane, used for its excellent resistance to UV.
Not all coatings work well together! A classic example is applying an alkyd coating over inorganic zinc, masonry or galvanizing; the high PH of the zinc forms a soap like material. Another common mistake is applying a chemical-cure coating over a solvent-evaporation cure coating. The strong solvents in the topcoat soften the undercoat; the stress of curing the topcoat pulls the softened material from the surface.
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