Corrosion, Galvanizing & Protective Coatings Guide

What causes steel to rust?

Bare iron or carbon steel can react with moisture and oxygen to form rust. Moisture provides a conducting film, allowing small electrochemical reactions across the surface. Salt and contaminants can make that film more aggressive. Rust is a corrosion product of the iron, rather than a protective finish.

A damp surface need not be visibly under water. Dew, condensation, wet vegetation and repeated wetting can sustain corrosion. A product’s appearance on delivery does not predict its durability at your site.

What is corrosion?

Corrosion is deterioration caused by a material reacting with its surroundings. Red-brown rust is associated with iron and steel; white staining on zinc has a different origin. Neither a stain’s colour nor a photograph alone establishes how much useful metal remains.

Assess the substrate, coating, affected area and service environment. Severe steel loss can reduce strength. Covering corrosion with paint does not restore lost steel or validate a fence’s structural capacity.

How does zinc protect steel?

Zinc provides a barrier over steel and can also corrode preferentially to protect small nearby exposed areas. This sacrificial or cathodic action is an important difference from an ordinary paint film. Its effectiveness depends on the remaining zinc, size of damage and environment.

Zinc protection is finite. A scratch should still be inspected and repaired where the specified system requires it; a large uncoated area cannot be assumed protected indefinitely by zinc elsewhere on the component.

What does galvanized mean?

Galvanized generally describes steel with zinc-based protection. It does not identify every detail of the coating. Continuously coated wire or sheet, pre-coated fabricated material and a completed fabrication dipped in zinc can have different processes and coating requirements.

Compare the applicable product specification, coating mass or thickness, process and test evidence. Silver appearance, the word galvanized and a heavy steel section are not proof that two products have equivalent corrosion performance.

How are zinc coating mass and thickness specified?

Coating mass is commonly expressed in g/m² and coating thickness in micrometres (µm). The measurement basis depends on the product and standard: sheet designations can describe a combined mass over both faces, while wire requirements refer to the coated wire surface. Compare like measurement bases.

For otherwise comparable zinc systems and exposure, a larger protective zinc reserve can extend useful protection. It is not a universal years-per-gram formula. Alloy density, coating distribution, adhesion, damage and environment matter; do not convert a label into a certificate.

Is wire diameter the same as zinc coating thickness?

No. Steel-wire diameter describes the wire geometry; coating mass describes its protection. A thicker wire does not automatically have more zinc per unit surface area. A thinner wire need not have a Standard galvanised coating.

Compare diameter and tolerance, tensile properties, roll length, net coil mass and coating separately. For mesh, also compare aperture, height, joints and manufacturing sequence. A strong wire with inadequate protection can still fail through corrosion.

What is Standard galvanised wire?

WFSA’s Standard galvanised wire has a Class C zinc coating. Compare its diameter-specific zinc coating mass with the Heavy galvanised Class A alternative. Select the coating for the actual exposure, intended use and project requirements.

Inland is not a universal reason to select a Standard galvanised coating. Irrigation, wet soil, animal waste, humidity and pollution can be aggressive far from the sea.

What is Heavy galvanised wire?

WFSA’s Heavy galvanised wire has a Class A zinc coating, with a higher minimum zinc coating mass than Class C Standard galvanised wire at the same diameter. Tensile grade, coating class and service life are separate considerations.

Greater protection warrants consideration for regular wetting, humid, coastal and aggressive agricultural exposure. Select the actual system and compatible ties, supports and fasteners together. No fixed lifespan is promised by the Heavy galvanised (Class A) or Heavy galvanised label.

What is hot-dip galvanizing?

A properly prepared steel article is immersed in molten zinc, allowing a zinc-based, metallurgically bonded coating to form. Preparation and inspection are part of the process. It differs from painting a zinc-coloured film onto steel.

For fabricated assemblies, suitable venting, drainage and accessible surfaces are essential for safe processing and coating coverage. Hollow sections and enclosed details must be designed with the galvanizer. Do not assume every internal cavity is protected simply because the outside looks galvanized.

Why does after-fabrication galvanizing matter?

The completed article is cut, formed, drilled and welded before galvanizing. With suitable design and processing, zinc can cover the resulting fabrication and its prepared welds and edges.

Later drilling, cutting or welding creates new damage outside that original process. Include the approved repair method and inspection in the installation specification. Batch galvanizing is a different product scope from continuously coated wire, sheet and certain automated tube processes.

What is pre-galvanized steel?

Pre-galvanized material is zinc-coated before final fabrication. It may be formed into tube or channel, or used as coated sheet. Its coating is useful protection, but later cuts, holes and welds need separate attention.

Selected pre-galvanized lipped-channel or tubing requirements may be available by enquiry; confirm the actual WFSA item and current availability. Do not infer after-fabrication treatment, internal coating coverage or coating mass from a PG label alone.

Hot-dip after fabrication vs pre-galvanized: what is different?

Neither process is universally best for every job. Specify when coating is applied, which surfaces are protected and how subsequent work will be treated. A smooth pre-coated finish and a batch-galvanized fabrication serve different product and fabrication needs.

What are Zn-Al / aluminium-zinc coatings?

Zinc-aluminium alloy coatings contain both metals, with composition varying by product. Zinc contributes sacrificial behaviour and aluminium contributes barrier and corrosion-resistance characteristics. The balance and performance depend on the particular alloy system and exposure.

Wire, roofing sheet and razor components must retain their own coating descriptions. Do not assign one alloy percentage or mass to every product described as Zn-Al, AZ or Aluzinc.

What do Aluzinc, AZ85, AZ100 and AZ150 mean?

Aluzinc-type and AZ descriptions identify aluminium-zinc coated material in relevant product systems. AZ coating numbers are coating-mass designations under the stated specification, rather than steel thickness or a warranty period. Their meaning and test basis must be confirmed for the product.

AZ85, AZ100 and AZ150 are not interchangeable. Where the applicable metric sheet specification uses those designations, the number relates to nominal/minimum coating mass in g/m² on its defined basis, commonly total over both faces. Do not apply that sheet convention automatically to wire. No specific AZ value is assigned to a WFSA item here without supporting product data.

What is powder coating?

Conventional decorative powder coating is generally an organic dry powder applied and heat-cured into a continuous finish. It can provide colour, appearance and a further barrier. Preparation, chemistry, thickness, cure and exposure govern the result.

On bare steel, damage that exposes the substrate can start corrosion. Powder coating alone does not automatically supply galvanizing’s sacrificial protection.

Can galvanized steel be powder coated?

Yes, when the galvanized surface is prepared and the selected powder system is compatible with it. Surface condition, contaminants and prior treatments affect adhesion. This needs a controlled coating specification, not simply any powder sprayed onto any zinc surface.

For specified WFSA Wholeview posts and gates, hot-dip galvanizing is the underlying corrosion-protection finish; powder coating adds colour and an outer barrier. Panel wire described as Aluzinc keeps that separate substrate description. Do not relabel all components as identical HDG material.

What is a duplex coating system?

A duplex system combines galvanizing with a compatible paint or powder finish. The organic layer adds a barrier and appearance while the underlying zinc retains its protective function. Properly specified together, they can improve overall protection.

The extra layer does not justify a universal lifespan multiplier or guaranteed years. Confirm each layer, preparation, application, handling, repairs and maintenance. Do not assume a painted item has galvanized steel beneath it unless the product specification says so.

What matters in a paint system?

Paint separates steel from the environment when its film remains effective. Preparation, primer, chemistry, number of coats, dry-film thickness and application quality are significant. A painted or black product title does not identify all those properties.

Confirm maintenance and touch-up methods compatible with the supplied system. The current painted farm gates are not automatically hot-dip galvanized under their finish. Raw palisade components require their specified protective system before unsuitable outdoor exposure.

What do PVC / polymer coatings provide?

Polymer coverings add an external barrier and can provide colour and handling characteristics. Their exact chemistry, application, thickness and substrate protection vary. Two green-coated wires can have different metallic coatings underneath.

A cut, crushed or abraded covering can expose the underlying layer. Do not use PVC, polymer, powder coating and Plascoat as synonyms.

What is Plascoat?

Plascoat describes a family of specialist thermoplastic powder coatings. A thermoplastic layer is formed by melting and fusing rather than the same chemical curing process used by conventional thermoset decorative powders. It is not a universal name for PVC.

Relevant systems can be evaluated for demanding outdoor, coastal or industrial exposure. A family name alone does not establish chemical compatibility, certification or service life.

Plascoat vs conventional powder coating: what should I compare?

Both may be applied in powder form, but they are not the same coating technology or an automatically equivalent finish. WFSA commonly evaluates conventional powder for colour/appearance and specified Plascoat for enhanced protective requirements.

Compare the complete system, not just the brand or colour. The chosen Plascoat grade does not make the whole installation immune to impact, cuts or every chemical exposure.

Is the Wholeview Plascoat warranty always 15 years?

No. Specified WFSA Wholeview Plascoat finishes can carry a coating warranty of up to 15 years, subject to the actual system, environmental classification, application, installation, project specification and written warranty conditions.

Up to 15 years, subject to coating system, environmental classification, application, installation, project specification and applicable warranty terms. A coating warranty is not a guarantee of structural capacity, animal containment or protection against unauthorised entry. No general long-term service-life warranty is implied for economy products unless specifically stated otherwise; applicable statutory rights remain.

Why does steel corrode faster near the coast?

Airborne salt deposits and moisture can make marine exposure particularly aggressive. Humidity and repeated wetting allow deposited chlorides to affect coatings, especially at damage, joints and sheltered areas where deposits accumulate.

Distance from the sea alone cannot establish a corrosion category. Wind, topography, shelter, rainfall washing, humidity and industrial contamination change local conditions. Describe the actual site to WFSA; compare suitable heavier metallic, Zn-Al, after-fabrication HDG, duplex or enhanced polymer systems for that product. No single coating is prescribed for every coastal application.

Does inland mean corrosion-free?

No. Rain, condensation, irrigation, wet vegetation, poor drainage, pollutants and standing water can make an inland location demanding. Classify the exposure and desired service life rather than selecting coating solely from the address.

A standard coating may suit some applications, but inland does not automatically make it technically sufficient or preferable. Review replacement access, inspection and consequences of premature loss alongside initial cost.

What corrosion factors matter on farms?

Consider irrigation, wet grass, animal waste, fertiliser storage, chemicals, trough areas and soil contact. Exposure can differ along one fence: lower wires and damp enclosed joints may deteriorate faster than freely exposed upper components.

Tell WFSA about known substances and cleaning procedures. Chemical resistance is system-specific; this guide does not promise compatibility with every fertiliser or farm chemical. Fire can damage coatings and wire properties independently of ordinary atmospheric corrosion.

How should industrial exposure be assessed?

Emissions, process chemicals, humidity and repeated wash-down can need a project-specific coating design. A coastal designation does not automatically cover every chemical or industrial environment.

Record known chemicals, concentrations, temperatures and wetting where relevant, then Choose compatible fasteners and maintenance access as part of the assembly. A generic finish or colour is not sufficient evidence for the required exposure.

What changes at soil and concrete interfaces?

Buried or soil-contact steel has different conditions from freely exposed atmospheric steel. Moisture, drainage, soil chemistry and local damage affect corrosion. A protective system acceptable above ground may need separate assessment at the interface.

Where the installation detail permits, finish concrete to shed water away from the post rather than making a water-trapping hollow. Keep the specified foundations and coating treatment. See the post and support guide; no universal buried-steel lifespan or foundation size is implied.

How do scratches and cuts affect protection?

A scratched zinc coating may still protect a limited nearby exposed area while enough zinc remains. Damage through paint, powder or polymer exposes the underlying system; if bare steel is reached, corrosion can start. Every system can be damaged.

Cut edges on pre-coated sheet, tube, channel, wire and mesh need the specified assessment and repair. Do not assume zinc elsewhere protects all exposed edges permanently. Inspect drilling, fastenings, weld areas and handling marks before handover.

Can galvanized steel be welded?

It can be welded using appropriate professional procedures, but heat damages coating around the weld and a compatible repair may be needed. Welding or cutting zinc-coated steel can produce hazardous zinc-oxide fumes and other welding hazards.

Use a competent welder with a suitable risk assessment, local extraction/ventilation and appropriate protective equipment. Confined-space work requires its own controls. This guide does not provide casual coating-burnoff or welding instructions.

What is galvanic corrosion?

Different metals electrically connected in the presence of moisture or another electrolyte can form a galvanic couple. One material can corrode faster. Severity depends on the metals, environment, contact arrangement and relative exposed areas.

Assess contact between zinc-coated steel, bare steel, aluminium, copper, stainless steel and other materials. Do not use a universal compatibility chart for all exposures. Isolation or a specified coating arrangement may be needed, especially where dampness persists.

Why do fasteners and fixing finishes matter?

A long-lasting panel or roof can still be compromised by unsuitable fasteners. Specify material, coating, contact compatibility and exposure for screws, clamps, clips, brackets and flashings, not just the main sheet or panel.

For Wholeview, include the fixator and screw system. For razor, assess tape, core and clips separately. For roofing, consider washers, flashings, contact materials and runoff. A stainless fastener is not automatically compatible with every surrounding metal and environment.

What is white rust on galvanized steel?

White or grey zinc corrosion products can form when coated material remains damp with restricted airflow, commonly in tightly nested or wet-stacked bundles. This is often called wet-storage stain; it is different from red steel rust.

Light staining is not automatically complete coating failure. Persistent or heavy deposits can consume protection and need assessment of remaining coating. Separate and dry affected material, address trapped moisture and obtain compatible cleaning or repair advice rather than using aggressive unverified chemicals.

How should coated products and roof sheets be stored?

Keep materials off wet ground, drain standing water and allow airflow. Avoid prolonged wet nesting or tightly wrapped damp bundles. Protect against chemical contamination and handling abrasion; covering a wet bundle without ventilation can retain the problem.

Roof sheets must not remain wet-stacked. Use the specified dry, ventilated storage and handling arrangements and review delivery conditions promptly. See the roofing guide for sheet planning and safe access considerations.

What should I specify for wire and mesh?

Compare wire diameter, tensile requirements, coating type/mass where stated, roll dimensions and usable length separately. For welded mesh For woven mesh and netting include support wires, ties and terminations.

WFSA supplies Standard galvanised Class C and Heavy galvanised Class A wire. Field-fence construction, wire diameter and tensile grade must be compared separately from the coating. See the relevant product guide and diameter-specific coating schedule.

What coating information applies to Wholeview?

WFSA manufactures its current Wholeview panels using Aluzinc wire and a 75 mm horizontal block width. High Secure uses 12.7 mm vertical × 75 mm horizontal block width; Medium Secure uses 25 mm × 75 mm; Secure uses 50 mm × 75 mm. Standard panel width is 3,000 mm and typical panel wire is 3 mm horizontal × 4 mm vertical. Panel substrate, optional PC finish and fabricated post/gate coating must be described separately.

Hot-dip galvanized Wholeview posts and gates are the standard base finish where specified. Powder may add colour; enhanced Plascoat requires its own system and project warranty terms. See the Wholeview guide, including shared-post fixator counts.

What should I check on razor wire?

WFSA manufactures Rhino Super Blade razor wire with Aluzinc strip and an Aluzinc core wire. This manufacturing description does not assign an unstated alloy percentage or coating mass. For any alternative

Specify compatible clips and attachments and assess cut edges, damage and safe maintenance. Do not assume the entire installation has one identical coating. Read the razor-wire guide for BTC, Flatwrap and coil coverage.

How are roofing thickness and coating different?

Steel substrate thickness and metallic coating mass are different properties. A 0.40 mm sheet label does not mean 0.40 mm of zinc.

A ZA or ECO label should not be silently expanded into an unverified alloy ratio, coating mass or certification. Compare profile, effective cover, thickness, coating, finish, fasteners and exposure. Read the IBR and corrugated roofing guide.

How do the main protective systems compare?

This table compares their roles, not a universal worst-to-best ranking. Actual performance follows the complete product specification and exposure.

How do I specify a coating for a quotation?

Provide the product, installation location, marine salt exposure, industrial or agricultural contaminants, wetting/irrigation, soil contact and required design or service life. State the desired colour, any project standard, certification and warranty requirement.

Tell WFSA whether cutting or welding will occur after coating and whether regular maintenance is possible. Identify the required metallic coating, outer finish and compatible fittings. Where a property is important, request its actual value and evidence rather than relying only on a trade label.

What common coating mistakes should I avoid?

Do not compare products by roll length or price alone; do not assume thick wire has heavy zinc; do not equate every galvanized product; and do not treat powder, PVC, Plascoat and metallic coating as interchangeable.

Avoid specifying only the visible panel while ignoring posts, ties, gates and fasteners. Do not apply a fixed lifespan to every environment or a historical certification to a current item. Confirm required properties before approving a substitution.

How do Mzansi / Econo ranges affect comparison?

Some economy products use standard coating specifications, but actual properties differ by item. Compare the same geometry, mass, mechanical properties and protection. An initial saving may involve a different product specification.

Mzansi / Econo is a respectful commercial-value description for suitable price-sensitive and general uses. Do not substitute it where a tender, engineer or customer requires a defined coating or certification. Read Understanding WFSA Product Ranges.

What should I inspect and maintain?

Check damage, red rust, coating breakdown, cuts, weld repairs, fastener corrosion, trapped water and chemical contamination. Include sheltered faces, connections, low wires and soil/concrete interfaces. Set frequency to exposure and site risk.

Use compatible cleaning and repair provisions, address the cause of recurring damage and keep the written maintenance requirements for any warranty. Coating touch-up does not restore lost steel strength. Service life depends strongly on coating specification and environmental exposure; no universal number of years is given.

Where can I find product-specific coating information?

Use the linked technical guides for actual WFSA labels, component arrangements and estimating. Then check the current product listing or contact the branch for the supplied specification and availability.

Raw Reinforcing Steel: Surface Discolouration and Damaging Corrosion

Reinforcing mesh, Y-bar and certain Brickforce products are supplied as raw or black steel without a protective zinc coating. When raw steel is exposed to humidity, rain, condensation, water or wet storage conditions, a light orange-brown layer of surface oxidation can develop quickly. Light surface rust is normal on uncoated reinforcing steel and does not by itself mean that the material is defective or unsuitable for use. Heavy flaky or scaly corrosion, deep pitting, or significant loss of steel section, mass or dimension is different and should be assessed against the applicable product and project specification.

This guidance applies to raw / black / uncoated reinforcement. Galvanized Brickforce, galvanized steel and coated reinforcement have separate protective-coating specifications and must be assessed accordingly. Surface oxidation does not establish steel grade, compliance or structural suitability; the applicable project specification and responsible engineer determine acceptance where required.

Read the reinforcing mesh and Y-bar surface-condition guidance and black-wire Brickforce guidance.

Frequently Asked Questions

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