Galvanized Steel Coating Thickness: G30 vs. G90—Selection Guide for Outdoor Use

Galvanized Steel Coating Thickness: G30 vs. G90—Selection Guide for Outdoor Use

Introduction to Galvanized Steel Coatings

Galvanized Steel is one of the most widely used materials in construction, infrastructure, and manufacturing thanks to its strong corrosion resistance and durability. The protective zinc coating that defines Galvanized Steel is the key to its long service life, particularly in outdoor environments. The thickness of this zinc coating is measured and classified by standards such as G30, G60, and G90. These codes indicate the amount of zinc applied per square foot of steel sheet. Among them, G30 and G90 are two of the most common designations, often compared when evaluating performance requirements for outdoor applications. Choosing between G30 and G90 involves understanding coating thickness, corrosion resistance, cost efficiency, and the expected exposure conditions.

Understanding Coating Designations in Galvanized Steel

What G30 and G90 Mean

The “G” designation refers to the weight of zinc coating per square foot of steel, expressed in ounces. A G30 coating means that approximately 0.30 ounces of zinc is applied per square foot of steel sheet (both sides total), while a G90 coating represents 0.90 ounces per square foot. The higher the number, the thicker the zinc layer and the stronger the corrosion protection.

Measurement of Thickness

The coating weight can be converted into coating thickness. G30 typically results in around 0.45 mils (0.011 mm) of zinc on each side of the steel sheet, whereas G90 results in approximately 1.35 mils (0.034 mm) per side. This difference in thickness directly translates into performance variations, particularly in outdoor or harsh environments where exposure to moisture, chemicals, and pollutants is high.

Why Thickness Matters

Zinc acts as both a physical barrier and a sacrificial layer. It corrodes preferentially to steel, protecting the substrate. The thicker the coating, the longer the steel remains protected before rusting begins. This sacrificial effect is vital in outdoor applications such as roofing, fencing, and building facades.

Performance Characteristics of G30 Coatings

Corrosion Resistance

G30 offers a basic level of corrosion protection, suitable for indoor or light outdoor applications. In environments with limited exposure to rain, humidity, and pollution, G30-coated steel can perform adequately. However, in consistently wet or coastal environments, its thinner coating may deteriorate faster.

Service Life Expectancy

In mild outdoor conditions, G30 can last for several years before red rust develops. In sheltered applications, such as under roofing or siding, its lifespan extends further. However, when directly exposed to the elements, G30 is not typically recommended for long-term durability.

Applications

G30 is commonly used in indoor environments, HVAC ductwork, appliances, and areas with controlled exposure to moisture. Its cost-effectiveness makes it attractive for projects where high corrosion resistance is not critical.

Performance Characteristics of G90 Coatings

Corrosion Resistance

G90 offers significantly stronger protection than G30 due to its triple coating weight. It provides reliable defense against rust in outdoor conditions, including urban, rural, and industrial environments. Its resistance is particularly valuable in regions with high humidity, acid rain, or frequent precipitation.

Service Life Expectancy

The thicker zinc layer of G90 translates into a much longer service life. Depending on the environment, G90 can last decades without requiring replacement or additional protection. In moderate climates, it may remain rust-free for up to 20–30 years, while in harsher environments, it still outperforms thinner coatings by a wide margin.

Applications

G90 is the preferred choice for roofing sheets, wall cladding, fencing, street furniture, and other outdoor applications where consistent exposure to moisture and pollutants is unavoidable. It is also widely specified in building codes for residential and commercial construction.

Comparing G30 vs. G90 for Outdoor Use

Durability in Outdoor Conditions

G30 is more prone to early rust formation in outdoor use because of its thinner protective layer. G90, by contrast, is engineered for durability in all weather conditions. For any structure where longevity and low maintenance are required, G90 is the superior option.

Cost Considerations

The main advantage of G30 lies in its lower cost. Thinner coatings reduce material and galvanization expenses, making it attractive for budget-sensitive projects. G90, although more expensive upfront, reduces long-term costs by extending service life and minimizing repair or replacement needs. The decision often comes down to whether upfront savings outweigh the potential cost of early degradation.

Compliance with Standards

Many building codes specify minimum coating thickness for certain applications. For example, roofing or siding in residential construction often requires G90 or higher to ensure durability. G30 may not meet these requirements in outdoor scenarios, limiting its suitability.

Environmental Conditions

The choice between G30 and G90 is heavily influenced by environmental conditions. In coastal or industrial areas with higher corrosive exposure, G90 is the only viable choice. In arid or indoor-adjacent outdoor spaces, G30 can sometimes be sufficient.

Life-Cycle Considerations

Maintenance Requirements

G30-coated steel in outdoor environments often requires additional protective measures, such as painting or regular inspections, to extend its service life. G90 requires far less maintenance, making it more appealing for large-scale or difficult-to-access structures.

Sustainability Aspects

Longer-lasting coatings reduce the frequency of replacements and resource consumption. G90, by offering superior longevity, aligns better with sustainability goals, even if its initial zinc usage is higher.

Total Cost of Ownership

When factoring in durability, maintenance, and replacement frequency, G90 usually offers lower life-cycle costs despite its higher upfront expense. G30 is only more economical when used in low-exposure conditions where its shorter lifespan does not pose a financial or safety risk.

Selection Guide for Outdoor Use

When choosing between G30 and G90 for outdoor projects, several factors should be weighed carefully. First is the environmental condition: humid, coastal, and industrial regions demand the higher protection of G90. Second is compliance: many building codes require G90 or higher for exposed outdoor applications. Third is project scope and budget: while G30 is cheaper, it may lead to higher long-term costs in exposed conditions. Finally, the intended service life of the structure should be considered. For temporary installations, G30 may suffice, but for long-lasting infrastructure, G90 is the clear choice.

Conclusion

The decision between G30 and G90 Galvanized Steel coatings for outdoor use comes down to balancing cost with performance requirements. G30 provides minimal corrosion protection and is suitable mainly for indoor or lightly exposed applications. G90, with its triple zinc coating thickness, offers superior durability, longer service life, and compliance with most construction standards. In nearly all outdoor conditions, G90 is the recommended option, ensuring reduced maintenance, sustainability, and long-term cost savings.

FAQ

What does G30 mean in Galvanized Steel?

G30 indicates a zinc coating weight of 0.30 ounces per square foot of steel sheet, which translates to a thin protective layer.

How thick is G90 compared to G30?

G90 has approximately three times the coating weight of G30, providing a zinc thickness of about 1.35 mils per side compared to G30’s 0.45 mils.

Is G30 suitable for outdoor use?

G30 is not generally recommended for outdoor use because it corrodes faster. It is better suited for indoor or low-moisture environments.

Why is G90 preferred in construction?

G90 offers stronger corrosion resistance, longer lifespan, and compliance with building codes for exposed outdoor applications.

How long does G90 last outdoors?

In moderate climates, G90 can last up to 20–30 years, while in harsher environments, it still outperforms thinner coatings significantly.

Is G90 more expensive than G30?

Yes, G90 costs more upfront due to thicker zinc coatings, but it reduces long-term expenses by minimizing maintenance and replacement needs.

Can G30 be painted for outdoor use?

Yes, painting G30 can extend its service life outdoors, but this adds maintenance requirements compared to using G90 directly.

Do building codes require G90?

In many regions, yes. Building codes often specify G90 as the minimum standard for roofing, siding, and other outdoor applications.

What industries commonly use G90?

Construction, automotive, infrastructure, and renewable energy industries widely rely on G90 for its durability in outdoor exposure.

Which option is more sustainable?

G90 is generally more sustainable because it lasts longer, reducing the frequency of replacements and conserving resources over time.