Trapezoidal sheet corrosion protection: methods, care & permanent solutions

Why corrosion protection is crucial for trapezoidal sheeting Corrosion protection is not a minor matter for trapezoidal sheeting, but is decisive for its entire service life. The thin sheet steel (0.5-0.75 mm) rusts within months without adequate protection. The first signs of rust quickly lead to rusting through - and thus to costly repairs.

This article explains which corrosion protection methods are available, how to choose the right coating for your environment and shows low-maintenance alternatives for extreme corrosion environments.

Why corrosion protection is crucial for trapezoidal sheet metal

The technical properties of trapezoidal sheet metal show the fundamental problem: with a sheet thickness of just 0.5-0.75 mm, the material rusts through within a few months as soon as the protective layer is damaged. Without galvanising and coating, trapezoidal sheeting would become unusable within a season.

Typical weak points:

• Cut edges: Cutting destroys galvanisation - rust after 1-2 years without subsequent treatment
• Screw holes: Water penetrates without proper sealing discs
• Mechanical damage: Any damage to the coating exposes steel
• Condensation: Moisture attacks the coating from the inside
• Contamination: Organic deposits retain moisture

Galvanising and coatings in comparison

Galvanisation classes (Z100, Z140, Z275)

Every trapezoidal sheet is galvanised. The zinc coating determines the protective effect:

Class	Zinc coating	Application class	Service life
Z100	100 g/m²	Indoors	10-15 years
Z140	140 g/m²	Standard Exterior	15-20 years
Z275	275 g/m²	Coast, industry, agriculture	25-30 years

Z275 costs 15-25 % more than Z140, but extends the service life considerably. Galvanising alone is not enough - UV radiation and pollutants attack zinc. Therefore, additional painting is required.

Coatings: Standard polyester, PVDF and plastisol

Painting protects galvanisation from UV radiation and extends the service life. Three quality levels are available:

Standard polyester (25 μm):

• Cheapest option, sufficient for normal environments (C2-C3)
• Service life 20-25 years
• Available in many RAL colours
• Limitations: In coastal, industrial or agricultural applications, often premature failure after 12-18 years

PVDF (35 μm):

• High-quality coating with fluoropolymers
• Better UV resistance, self-cleaning effect
• Service life 30-40 years
• 30-50 % more expensive, but recommended for corrosive environments (C4-C5)

Plastisol (200 μm):

• Thickest coating (8 times thicker than standard)
• Maximum mechanical protection
• Service life 30-40 years
• Mainly for industrial buildings with mechanical loads

Coating thickness	Service life	Corrosion protection	Surcharge	Best application
Standard polyester	20-25 years	C2-C3	-	Normal environments
PVDF	30-40 years	C4-C5	+30-50 %	Coastal, industry, agriculture
Plastisol	30-40 years	C3-C4	+40-60 %	Mechanical load

Environmental requirements and correct selection

The ISO 12944 standard defines corrosion categories (C1-C5) based on environmental stress:

Category	Environment	Recommended coating
C2	Rural areas	Z140 + standard polyester
C3	City, coast > 10 km	Z140 + standard polyester or Z275 + PVDF
C4	Industry, coast 3-10 km	Z275 + PVDF
C5	Coast < 3 km, chemical industry	Z275 + PVDF or plastisol

Near the coast: Salty air is extremely corrosive. At a distance of < 10 km from the sea, Z275 + PVDF is mandatory. Standard polyester fails after 12-15 years.

Agriculture: Ammonia from stables severely corrodes zinc and coatings. Minimum: Z275 + PVDF. Optimal: Sandwich panels for agricultural operations with aluminium or GRP inner shell.

Industrial areas: Air pollutants (SO₂, NOₓ) require Z275 + PVDF. Regular cleaning every 2-3 years extends service life.

Maintenance and economic efficiency

Inspection and minor repairs

Inspection intervals:

• Normal environments (C2-C3): Every 3-5 years
• Corrosive environments (C4-C5): Every 1-2 years

What to look out for: Rust deposits (cut edges, screws), colour changes, soiling, brittle seals, condensation on underside.

Repair minor damage: Remove rust (wire brush), clean surface, apply zinc dust paint, top coat. Costs: €20-50 per spot. Preventive repair is 10-20× cheaper than later restoration.

Re-treat cut edges: Treat with zinc dust paint immediately after each cut on site - otherwise rust after 1-2 years.

Subsequent painting

Coating shows signs of ageing after 15-25 years. Subsequent painting costs 30-50 €/m² (cleaning + primer + 2× top coat + labour time) and extends service life by 5-10 years. Important: Only useful if the galvanisation is intact. Sheet metal that has rusted through over a large area cannot be renovated economically.

Cost comparison over 25 years

Maintenance costs add up. Example 200 m² roof:

Standard polyester: € 2,000 material + € 1,600 inspections + € 2,000 repairs + € 6,000 repainting = € 11,600 over 25 years

PVDF: €3,000 material + €1,000 inspections + €600 repairs = €4,600 over 25 years

High-quality coating saves € 7,000 despite higher purchase price.

All cost figures are rough guidelines and can vary greatly depending on the region, project size and specific requirements. For a precise calculation, we recommend an individual consultation.

Low-maintenance alternative: sandwich panels

For buildings in extremely corrosive environments, sandwich panels for roofs and sandwich panels for walls offer fundamental advantages:

Double protection: outer shell + PIR insulation core + inner shell. Even if the outer shell shows signs of corrosion damage after decades, the inner shell remains intact. The insulation core acts as a buffer - moisture does not penetrate to the inner shell.

Mechanical protection: The insulation core protects the inner shell from mechanical damage (hail, branches). Outer shell can be damaged - building remains tight.

Low maintenance: Closed system without cut edges, sealed at the factory, no condensation, no corrosion from the inside. Inspection intervals 3-7 years instead of 1-3 years.

Cost-effective for high corrosion requirements:

Example 200 m² roof, near the coast (C4), 30 years:

Trapezoidal sheet PVDF: € 3,000 material + € 8,000 substructure + € 6,000 maintenance + € 6,000 repainting = € 23,000

Sandwich panels 80 mm: € 6,000 material + € 5,000 substructure + € 3,000 installation + € 1,500 maintenance = € 15,500

Savings: € 7,500 over 30 years despite higher material costs.

Further details on the structure and properties of sandwich panels.

All cost figures are rough guidelines and can vary greatly depending on the region, project size and specific requirements. For a precise calculation, we recommend an individual consultation.

Conclusion: The right corrosion protection for your requirements

Normal environments (C2-C3): Z140 + standard polyester offers 20-25 years of service life at a moderate cost.

Corrosive environments (C4-C5): Z275 + PVDF costs 40-50% more, but extends service life to 30-40 years and significantly reduces maintenance. TCO analysis shows: More economical in the long term.

Extreme environments (coastal, agricultural, chemical): Sandwich panels as the better choice. Double corrosion barrier, mechanical protection, low maintenance. Higher initial costs are amortised by drastically reduced maintenance costs.

Our recommendation: Calculate the total costs over the service life, not just the acquisition costs. Seek individual advice on which corrosion protection is best for your requirements.

Last updated Nov 2025