Steelwork

6.5.3Steel grade and coatings

Steelwork shall be specified to provide sufficient strength, durability, and fire resistance.

The design should detail the method of fixing or connecting structural steelwork. The guidance given in this chapter applies to steelwork which is to be bolted (using black bolts) or not connected.

Steelwork should be in accordance with the guidance in this chapter and:

  • BS 4 Part 1 ‘Structural steel sections: Specification for hot-rolled sections’, or
  • BS 4848 ‘Specification for hot-rolled structural steel sections’.

To ensure adequate durability in the environment it will be exposed to steelwork should:

  • have a protective coating system applied before being delivered to site
  • comply with the level of fire resistance required by building regulations.

Where welding is to be carried out, the protective coating system specified by the designer should be used.

Further guidance on the protection of structural steel is given in BS EN ISO 12944 ‘Paints and varnishes. Corrosion protection of steel structures by protective paint systems’ and BS EN ISO 14713 ‘Protection against corrosion of iron and steel in structures’.

Decorative finishes should be compatible with the protective coat specification. The designer should determine compatibility in accordance with the manufacturer’s recommendations. Chapter 9.5 ‘Painting and decorating’ contains further guidance for decorative paint finishes to steelwork.

Table 4: Environment categories for component groups in different locations and exposure conditions

Notes

1 For construction located within 500m of coastal shoreline.
2 Alternatively, steelwork may be encased in concrete.
3 For steelwork not in contact with the ground.
4 For steelwork in contact with, or embedded in an external masonry wall, for at the contact / embedment length.

Alternatively, guidance on suitable atmospheric corrosivity categories (C1 – C5) and appropriate protective coatings for domestic construction may be based on the recommendations given on the website www.steelconstruction.info. A site specific assessment is required in order to determine an appropriate classification level for the steelwork. A suitable protective coating specification is to be determined by the designer in accordance with the coating manufacturer’s recommendations.

Table 5: Protective coatings for hot rolled structural steelwork for atmospheric corrosivity category (recommended for housing applications only)

Notes

1 Where steelwork is to be given a decorative finish, the protective coat is to be compatible with the decorative finish.
Manufacturers’ recommendations should be followed.
2 Where steelwork is to be protected by intumescent paint for fire purposes, manufacturers’ recommendations should be followed.
3 All fixings and fittings to the structural steel elements are to be protected against corrosion in a manner that is both commensurate and compatible with the
protective coatings.
4 Surface preparation to BS EN ISO 12944-4.
5 Coating thicknesses given represent nominal dry film thickness (d.f.t.).
6 Thicknesses and weights shown represent the coating to be applied to each face of a steel section.
7 Epoxy primers have a limited time for over-coating. Manufacturers’ recommendations should be followed.
8 80 µm can be in one coat or as 20 µm pre-fabrication primer plus 60 µm post-fabrication primer.
9 Alternatively, use products manufactured from austenitic stainless steel in accordance with the recommendations of BS EN 1993-1-4:2006.

Where shop-applied protective coatings have been damaged, the coatings should be made good on site prior to being built into the works, as indicated in Table 5 ‘Making good of damaged areas’.

Where steelwork is to be welded, the protective coating system specified by the designer should be used.

Where steelwork is to be protected by intumescent paint for fire purposes, this should be in accordance with the manufacturer’s recommendations.