Hot-dip galvanizing or painting: how to protect steel

In hot-dip galvanizing, cleaned steel is dipped into molten zinc at about 450 °C. The zinc bonds metallurgically with the steel and also covers edges, corners and the inside of vented hollow sections. If the surface is scratched, the surrounding zinc keeps protecting the steel. EN ISO 1461 sets the requirements and minimum coating thicknesses.

• A good choice outdoors and where maintenance is difficult.
• The surface is grey and metallic; there is no choice of colour.
• The size of a part is limited by the size of the galvanizing bath.
• Hollow sections need holes for air to escape and zinc to drain; these must be on the drawing.
• Thin, large plate parts can distort from the heat.

At Novatex, galvanizing (hot-dip, or electro-galvanizing when needed) is done through trusted partners.

A paint system usually consists of a primer, an intermediate coat and a top coat. EN ISO 12944 helps you choose the system based on two questions: how aggressive the environment is (corrosivity categories C1 to C5 and CX) and how long the protection must last (durability L up to 7 years, M 7 to 15, H 15 to 25 and VH over 25 years). Before painting, the surface is usually abrasive blast cleaned.

• Any colour, for example from the RAL range.
• No bath limits the size of the part.
• Damage can be repaired on site.
• A fire-protective coating is a paint system of its own, its thickness depending on the fire resistance required and the section.

Novatex paints in-house with wet paints, in various paint systems, including fire-protective coatings.

Where both a long service life and a specific colour are needed, a duplex system is used: the steel is hot-dip galvanized and then painted. The galvanized surface has to be prepared properly before painting so the paint holds. A duplex system costs more than either solution alone, but protects longer than either on its own.

Powder coating is applied as a powder and cured in an oven. The finish is even and durable, but the part has to fit in the oven, so it suits smaller parts better than large steel structures. In our workshop we use wet paints.

• Indoors, dry and heated: a simple paint system is often enough, or no corrosion protection is needed.
• Outdoors, hard to maintain: hot-dip galvanizing or a duplex system.
• A specific colour needed: painting or a duplex system.
• A fire requirement: a fire-protective coating, compatible with the substrate and the rest of the paint system.
• A very large or long part: painting, if the part doesn't fit in the galvanizing bath.

Put the corrosivity category, the durability required, the colour and, if needed, the fire resistance class on the drawing or in the request. That makes quotes comparable; see also what affects the cost of a steel structure. Send your drawings with the quote form and we will send you a quote. What we build: special metal structures and construction structures.