How to Verify the Real Coating Weight of Galvalume Coils – A Guide for South American Buyers

📅 Published: July 30, 2026 | By Fanda Steel

For buyers across South America — from Chile and Peru to Brazil and Colombia — Galvalume steel coils have become a trusted material for roofing, wall cladding, and industrial building projects. The aluminum-zinc alloy coating (AZ) provides superior corrosion resistance, especially in coastal environments where salt spray and high humidity are constant challenges.

However, a recurring problem has emerged in recent years: many buyers receive Galvalume coils with coating weights far below the specified AZ100 or AZ150 standard. The contract says AZ150. The invoice says AZ150. But what actually arrives is often AZ20 or AZ30 — a fraction of the required coating thickness.

This is not a quality issue. This is a specification issue. And it's costing buyers real money in shorter roof life, premature corrosion, and unexpected maintenance.

This guide is designed to help South American buyers understand what AZ coating means, why it matters, and how to verify that you are actually receiving what you paid for.

What Does AZ100 / AZ150 Actually Mean?

AZ stands for Aluminum-Zinc coating, measured in grams per square meter (g/m²) on both sides of the steel sheet.

AZ150 is a measurable specification, not a subjective quality grade. It is defined by international standards (such as ASTM A792) and can be precisely verified through physical testing. This means when you specify AZ150, you are not asking for "better quality" in a vague sense — you are asking for a specific coating weight that can be measured, documented, and confirmed.

For buyers, this distinction is critical because it affects how you verify what you receive. A "quality grade" can be subjective. A measurable specification like AZ150 either meets the standard or it does not. This is why testing matters — and why some suppliers are able to offer lower prices by delivering AZ30 while still claiming "good quality."

For coastal roofing, AZ150 is the recommended minimum. AZ100 may be acceptable in low-humidity areas, but for any project within 5km of the coast, AZ150 offers the necessary corrosion protection.

The difference is not small. AZ150 has more than seven times the coating weight of AZ20. The service life difference can be measured in decades.

What Some Buyers Have Experienced

Over the past several years, a number of buyers in Chile, Brazil, Colombia, and Peru have shared similar stories:

• A contract specifying AZ150
• A low price that seemed too good to pass up
• A delivery that arrived on time
• But a product that, when properly tested, showed only AZ20–AZ30 coating

The steel looks similar. The surface finish may look acceptable. But the protective coating — the very reason for specifying AZ150 — is missing.

The result: roofing that begins to show corrosion within 2-3 years instead of 20-30 years.

Some buyers have also reported:

• Short-shipped quantities (20-30% less than ordered)
• Quality samples provided for verification that did not match bulk delivery
• No response after payment was completed

These are not isolated cases. They are a pattern that has damaged trust in the market and made it more difficult for honest suppliers to compete on value rather than price.

Why Low Price Often Means High Risk

Some suppliers are able to offer the lowest price because they know exactly which corners to cut. For buyers who are focused only on price, these corners are rarely visible until it's too late.

The Limitation of Third-Party Inspections

Many buyers have told us: "But we used a third-party inspection company. They said the product was acceptable."

This is a common misunderstanding. Third-party inspections are valuable, but they have limitations.

• Sampling matters – Some suppliers know exactly where inspectors will take samples and can prepare those specific samples to meet specifications while the rest of the shipment does not.
• Coating testing is destructive – A proper coating weight test requires cutting a sample from the coil. Some suppliers will only allow samples from the outer wraps, which often have better coating than the core.
• Not all inspectors are equal – The skill and integrity of the inspector can vary.
• Testing is a snapshot – A sample test tells you about that sample, not about every meter of the coil.

How to Protect Your Purchase

1. Know what you are buying

• Understand that AZ150 is a real specification, not a quality grade
• Understand the service life difference between coating levels
• Ask the supplier: "What is your standard deviation for coating weight?"

2. Work with suppliers who are transparent

• Ask for the Mill Test Certificate (MTC) before shipment, not after
• Request a video of the coil being weighed and measured
• Ask to see the production line

3. Consider the total cost, not just the unit price

• Compare the delivered price per ton of usable material
• Factor in the expected service life for your specific environment

4. Build a relationship with a single supplier

• Consistency in quality often requires consistency in relationship

What a Responsible Supplier Looks Like

• Can clearly explain the difference between AZ100, AZ150, AZ200
• Provides actual test results with each batch
• Welcomes third-party inspections
• Shares Mill Test Certificates before payment
• Provides references for similar projects

Need to Verify Your Next Order?

• Request a sample – small cut samples are available for testing
• Ask for the MTC before payment
• Ask us about our quality control process – we can share photos and videos
• Request references from other South American buyers

About Fanda Steel

Fanda Steel (Shandong Fanda New Materials Co., Ltd.) is a manufacturer and exporter of steel coils, roofing sheets, and highway guardrail systems with over 15 years of industry experience. We supply to more than 30 countries worldwide, with a growing presence in South America.

Our focus is simple: deliver the quality we promise, on time, every time.