Zinc spray corrosion protection is the umbrella term for sprayable coatings with a high zinc content that protect steel from rust. They are used wherever hot-dip galvanised components have an exposed area after welding, drilling or cutting, or where bare steel needs a primer with active protection. This guide explains the working principle, distinguishes zinc spray from zinc-aluminium spray and anti-rust primers, and describes professional application.

How zinc spray achieves corrosion protection: the cathodic principle

Steel rusts when iron oxidises in the presence of water and oxygen. In the electrochemical series, zinc is less noble than iron. If both metals are in conductive contact and are wetted by an electrolyte such as rainwater or condensation, the zinc dissolves preferentially and the iron remains protected. The zinc becomes the sacrificial anode, the steel the cathode. This is known as cathodic corrosion protection.

This mechanism distinguishes zinc spray from a pure barrier coating:

A barrier such as a top coat keeps water and oxygen away from the steel. If it is damaged, the steel rusts at the damaged spot and the rust creeps under the coating.
Cathodic protection continues to work at small defects and scratches as long as zinc is still present in the surrounding area. The steel remains protected at the edge and under-rusting is slowed down.

The prerequisite is metallic contact between the zinc particles and the steel. This is why the zinc content in the dry film must be high and the surface must be bright metal and free of grease before application. According to the product description, the zinc spray from the Aerosols Germany range is formulated with over 92 % zinc in the dry film and is therefore electrically conductive, which also makes it suitable as a spot-welding paint.

Zinc spray, zinc-aluminium spray or anti-rust primer?

All three product groups serve corrosion protection but pursue different aims.

Product	Working principle	Typical use	Appearance
Zinc spray	Cathodic protection through high zinc content	Primer on bare steel, repair of galvanised parts, weld seams	Matt grey, similar to hot-dip galvanising
Zinc-aluminium spray	Zinc as sacrificial anode, aluminium pigments for weather protection and appearance	Initial preservation and repair of galvanised surfaces, visible cut edges	Lighter, metallic silver
Zinc touch-up	Zinc-containing paint, colour-matched to fresh galvanising	Visible welds and cuts on galvanised parts, top coat possible without primer	Almost identical in colour to freshly galvanised parts
Anti-rust primer with rust converter	Barrier plus chemical conversion of residual rust	Rusted surfaces that cannot be fully de-rusted	Red-brown, intended for overcoating

Zinc spray

Zinc spray is the first choice when active protection is the priority: weld seams, drilled holes, connection surfaces and all places where the hot-dip galvanising has been damaged. It is intended as a corrosion protection primer for common metal parts and is suitable for repairing galvanised steel surfaces.

Zinc-aluminium spray

Zinc-aluminium spray combines the zinc content with aluminium pigments. The aluminium flakes overlap like scales and improve weather resistance as well as the appearance, which is closer to fresh galvanising. It is used for initial preservation and repairs on galvanised surfaces, is heat-resistant and, according to the product description, adheres well to common metals.

Zinc touch-up

Where appearance is decisive, for instance on railings, fences or facade components, the zinc touch-up gives a result that is almost identical in colour to freshly galvanised parts. According to the product description, it can be overcoated without a primer.

Anti-rust primer

An anti-rust primer such as the Rust-Stop long-term primer red-brown works differently: it contains a rust converter, penetrates residual rust and forms an overcoatable primer. It is the right choice when a component is already rusted and cannot be fully blasted to bright metal. It does not provide cathodic protection.

Repairing galvanised parts

Hot-dip galvanised components are frequently reworked on site or in the workshop. Every drilled hole, every cut and every weld seam exposes bare steel. Corrosion starts there because the protective effect of the surrounding galvanising only reaches over a short distance. Repair with a zinc-containing coating is common practice in structural steelwork and is described in standards for hot-dip galvanising as a repair method. The requirements that apply in each case are defined by the client or the execution specification.

For a lasting result:

Remove welding slag, scale and spatter mechanically.
Sand the damaged area and a transition zone of the intact galvanising so that the edge is not left stepped.
Degrease thoroughly and remove sanding dust.
Apply zinc spray in several thin coats until the area is evenly covered. Observe the flash-off times on the label.
On visible surfaces, then use zinc-aluminium spray or zinc touch-up for an appearance matched to the galvanising.

Preparation: the decisive step

No corrosion protection holds on grease, rust or loose coating. Preparation determines the service life of the coating more than the film thickness does.

Degreasing: remove oil, grease, cutting fluid and perspiration with a degreaser or industrial rapid cleaner. Do not touch with bare hands afterwards.
De-rusting: remove loose rust with a wire brush, abrasive fleece or blasting. Zinc spray requires a bright metal substrate so that cathodic contact is established.
Drying: moisture in pores and gaps prevents adhesion. Keep the substrate dry and free of condensation and observe the working temperature on the label.
Masking: cover adjacent components, threads and sealing surfaces.
Shaking: zinc pigments settle. Shake the can for as long as the label specifies, also at intervals during longer jobs.

Testing the protective effect

The durability of corrosion protection coatings is determined in the laboratory, among other methods, in the salt spray test. The procedure is now described in DIN EN ISO 9227; some older product data still refer to the earlier national standard. The result of such tests depends on film thickness, substrate preparation and test conditions and cannot be converted directly into an outdoor service life. For adhesion, the cross-cut test is frequently used. Such values are only meaningful if they relate to the specific product and to the information in the technical data sheet.

Limits of zinc spray

A zinc spray does not replace hot-dip galvanising. The film thickness from the can is lower, and the coating is mechanically less robust than an alloy layer formed in the zinc bath. For large-area new protection or parts permanently exposed to water, hot-dip galvanising, duplex systems or multi-layer coating systems are preferable. Zinc spray is the tool for repairs, priming and smaller areas. Suitable top coats are those that adhere to zinc-containing primers; a preliminary test on a concealed area is recommended.

Zinc spray for industry, trade and own brands

Aerosols Germany supplies zinc spray, zinc-aluminium spray, zinc touch-up and anti-corrosion primers, produced in Europe and quality-checked in Iserlohn, for structural steelwork, metal fabrication, industry and trade. The products are also available under your own label.

Do you need zinc spray for series repair work, are you looking for a formulation with specific properties or are you planning a corrosion protection programme under your own brand? Then send your enquiry to Aerosols Germany and we will advise you on product selection, data sheets and filling.

Zinc spray as corrosion protection: how it works, selection, application