Shop primer
For internal steel in a warm, dry building - most beams in houses, offices and shops - a shop-applied primer is normally sufficient, particularly where the steel will be boxed in. It is the quickest and most economical option.
Hot-dip galvanising
For external or exposed steel - balconies, external stairs, gates, railings, canopies and steel in damp locations - hot-dip galvanising is the standard choice. The fabricated steel is dipped in molten zinc, forming a tough, metallurgically bonded coating inside and out, to BS EN ISO 1461. Galvanised steel can last for decades outdoors with minimal maintenance.
- Steel must be fully fabricated before galvanising - welding afterwards damages the coating
- Hollow sections need vent and drain holes, designed in by the fabricator
- Galvanising can cause slight distortion in thin or long pieces
Powder coating and duplex systems
Where colour matters - balustrades, gates, feature metalwork - a powder coat or paint system can be applied over galvanising. This "duplex" system combines the corrosion protection of zinc with a decorative finish, and typically outlasts either system on its own.
Intumescent fire protection
Intumescent paint is a fire protection coating rather than a corrosion coating. When heated it swells to insulate the steel, giving a stated period of fire resistance. It is used where steel needs fire protection but will remain visible. Thickness is specified for the section and fire rating required.
Quick guide
- Inside, dry, boxed in: shop primer
- Outside or damp: hot-dip galvanised
- Outside and coloured: galvanised + powder coat (duplex)
- Visible and needs fire rating: intumescent coating
We shop-prime in-house and manage galvanising, powder coating and intumescent through specialist partners, so you get one price and one point of contact.