Inspection/planning

It is essential that complicated structures are regularly inspected and problem areas dealt with before any breakdowns spread to the overall coating.

Maintenance planning

Good maintenance involves the rectification of areas which have failed even when these areas are a small percentage of the total structure. It is vital that the failed areas be built up so that their coating thickness is equal to or more than that of the sound areas. Do not start by specifying a number of coats overall as this will not give a build-up of failed areas. Overall coats will tackle perhaps only 20% of the problems although the bill will be for 100%. With this approach re-coating becomes a largely cosmetic exercise. It should be noted that maintenance systems generally do not last as long as the original surface coating because the preparation will not be as good as on the new metal. However if the preparation for maintenance is more thorough (usually involving blast cleaning) normally a thicker film needs to be applied to cover the resulting rougher surfaces that are given by open-gritblasting compared to mechanical shot-blasting processes. This will then provide a level of protection comparable to systems applied to new steel.

System choice

Numerous factors need to be assessed before selecting and specifying a protective coating system. The key areas are:

• Surface preparation: blast cleaning power-tool or hand-tool cleaning
• Where the coating is to be applied - at the fabricator's premises or on site
• Environmental conditions of service - Application methods used

When it is a question of repeating the existing system areas of breakdown should be made good before coating overall. Where frequent repainting is being carried out consider an upgrade to lengthen the periods between repaints. Some situations require more repaints than maintenance demands such as food factories. If there is a high incidence of mechanical abrasion consider an upgrade to the system and the preparation - or repaint more frequently.

Primers are key products as they provide the foundation of the total system. They are applied direct to the steel and therefore must be compatible to the surface preparation method and the standard of cleanliness which it makes available. In addition they must be the main anti-corrosion mechanism whilst being compatible with the finishing system. Selection must also take into account the sequence / drying time of the total coating process.