Type of protection to be used 1241 General

The following notes may assist in determining the type of system which is appropriate for a particular application and exposure:

• Protection requirements are generally minimal inside dry, heated buildings, such as offices, shops and schools. In such situations, no protection is required, except for decorative reasons, unless the steelwork is located within a cavity wall (see below).

• Some interior steelwork may be exposed to condensation, particularly in sports halls, exhibition halls and workshops. Although these environments are generally classified as mild, a protection system will generally be required for visual reasons.

Where steelwork is exposed to industrial processes, or encloses humid areas such as swimming pools, the environment should be classed as 'severe' and specialist advice should be sought. The system chosen will depend on the particular environment and atmospheric contaminants.

Perimeter steelwork enclosed in cavity walls can be subdivided into two categories:

— where an adequate air gap (40 mm minimum) exists between the steel and the outer masonry skin, then adequate protection can be achieved by a simple painting system. This gap can be reduced to 25 mm if an impermeable thermal insulation is placed between the steelwork and the outer leaf. Suitable materials include closed cell organic foams, such as polyurethane phenolic based or extruded polystyrene

— where the steelwork is in contact with, or embedded in, the outer leaf of the wall, then a high-quality surface protection system should be applied. Bitumen-based coatings (site applied) and coal tar epoxies (shop applied) are common. Alternatively, for severe environments, the steel can be galvanized and painted with bitumen-based paint to prevent the galvanized surface coming into contact with the masonry.

Where the steelwork is fire protected, consideration must be given to the compatibility between the corrosion and fire-protection systems. For boarded fire-protection systems, this will generally not be a problem. Mineral fibre or particle-sprayed systems should generally not be used on galvanized steelwork due to adhesion problems. Where intumescent paints are used, it is vital that the compatibility is checked with the paint manufacturer.

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