How to Seal a Metal Roof Against Water Leaks

Key Takeaways:

Why Metal Roofs Leak: Metal roofs are prone to leaks because constant thermal expansion and contraction put stress on seams, joints, and sealants over time.
Products to Look For: The best products are professional-grade, flexible, and waterproof sealants that are engineered for the constant movement of metal.
Why Tradies Trust Soudal: Construction workers choose Soudal products for their superior adhesion, elasticity, and UV resistance

Sealing a metal roof against water leaks is an essential skill for any tradie. The last thing you need is a callback for a serious leak or failed sealant. But the truth is that thermal expansion, UV exposure, and general wear and tear make metal roofs particularly vulnerable.

At Soudal, we believe that getting the job done right doesn’t have to be a headache. This guide walks you through how to seal a metal roof against water leaks for a long-lasting and reliable fix. We’ll show you why professional-grade products are essential and introduce you to the best roof sealants for metal roofs.

Why Metal Roofs Are Prone to Leaks

When you’re called out to fix a roof leak, the problem is rarely the metal itself. It’s usually a failure of its weakest points. Here are the most common reasons metal roofs start to leak.

Thermal Expansion: Metal heats up and cools down with the sun, causing it to expand and contract. This constant movement puts serious stress on seams, joints, and fasteners, eventually cracking and breaking a sealant’s bond.
Poor Installation: A rushed or incorrect job can lead to misaligned panels or improperly sealed fasteners and flashing. Even a small gap is an open invitation for water.
Corrosion: Over time, rust can form on fasteners and panels, creating pinholes that let water in.
Weather Damage: Hail, high winds, and heavy rain can damage sealant beads and dislodge fasteners, creating new entry points for water.

What Are the Best Sealants for Roof Leak Repair?

Facing a leak? Don’t grab just any product. The best sealants are purpose-built for metal roofing, with the durability and flexibility to handle the elements. Here are our top recommendations.

Soudal BlackJack Bituminous Joint Sealant

A heavy-duty, bituminous-based sealant, Soudal Blackjack Joint Sealant is custom-designed for demanding waterproofing tasks.

Heavy-Duty Waterproofing: Provides a robust, waterproof seal for key areas like joints, eaves, and gutters.
Strong Adhesion: Bonds exceptionally well to metal surfaces, asphalt shingles, and plastics.
UV Resistance: Designed to maintain stability and performance when exposed to sunlight.
Best For: Sealing and repairing leaks on metal and asphalt roofs, weatherproofing flashing, and emergency repairs.

Soudal Roof & Gutter Silicone

As a high-performance silicone sealant, Soudal Roof & Gutter Silicone is engineered to provide long-lasting, flexible protection for roofing and guttering systems.

High Flexibility: Remains permanently elastic to accommodate the thermal expansion and contraction of metal roofs.
Strong Adhesion to Metals: Bonds effectively to aluminium, stainless steel, Colorbond®, and other common roofing materials.
Weather and UV Resistance: Highly resistant to harsh weather and UV exposure, ensuring durability and longevity.
Best For: Sealing roof joints, gutters, flashings, and downpipes where flexibility and a waterproof seal are crucial.

Want to see Soudal Roof & Gutter Silicone in action? Check out this handy tutorial on How to Repair Leaking Gutter Connections.

When to Apply Sealant to Your Metal Roof

Knowing the right time to seal is just as important as using the right product. To ensure a long-lasting, watertight seal, here are the best times to apply sealant.

During Installation: The ideal time for pre-emptive sealing is right after a new metal roof is installed. This protects all seams and fasteners before they can be exposed to the elements.
During Routine Maintenance: Make sealing a part of your regular maintenance schedule. By inspecting and re-sealing every few years, you can prevent small issues from becoming major leaks.
After a Storm: Always perform a full roof inspection after severe weather. High winds, hail, and heavy rain can damage existing seals, and a quick touch-up can prevent a serious problem down the line.
At the First Sign of Wear: Reapply sealant when you see signs of wear, such as cracking, peeling, or a loss of elasticity. Regular checks on high-stress areas like valleys and flashings are crucial for maintaining continuous protection.

Ready to Get the Job Done Right?

For long-lasting roof protection and easy application, trust Soudal’s range of professional-grade sealants.

Whether you’re tackling a full re-sealing job on a metal roof with Gorilla Blackjack Sealant or just need a flexible, reliable seal for gutters with Soudal Roof & Gutter Silicone, you can count on a professional finish that lasts. With Soudal, you get a solution that stands up to the elements, prevents costly callbacks, and ultimately, protects your hard-earned reputation.

Explore the full range of Soudal roofing sealants today and find the perfect product for your next job.

FAQs

Do metal roofs need to be sealed?

Yes, absolutely. Even though metal roofs are durable, the seams, joints, and fasteners need to be sealed to prevent water from getting in and causing rust or leaks. This constant movement from thermal expansion puts stress on the seals, making regular maintenance crucial for long-term protection.

What is the best way to seal a metal roof?

The best way is to use a high-quality, flexible sealant specifically designed for metal roofing, ensuring you properly clean and prepare the surface before application. A professional-grade sealant like Soudal Roof & Gutter Silicone will remain elastic through a wide range of temperatures, preventing cracks as the metal expands and contracts.

How to repair a leaking metal roof without replacing it?

Locate all sources of the leak and apply a high-performance sealant to properly seal seams, joints, and penetrations. For a lasting fix, a product like Gorilla Blackjack is ideal, as it’s designed for heavy-duty repairs and can seal problematic areas without you having to replace the entire roof.

What can be used to seal leaking metal?

To seal leaking metal, use a professional-grade sealant like a hybrid polymer or silicone that offers strong adhesion and long-term flexibility to handle the metal’s natural expansion and contraction. For heavy-duty jobs, a bituminous-based sealant like Gorilla Blackjack is often the ideal tool for a durable, watertight seal.