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’s our top recommendation. 

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.

How to Seal a Metal Roof: A Step-by-Step Guide

With the right approach and a quality product, you can seal a metal roof for good. This 8-step guide walks you through the entire process, from finding the right sealant to making sure the job is done right.

Step 1: Plan and Choose the Right Weather

Before starting any work, select a period of mild and dry weather. Extreme heat, strong winds, or rain can compromise the sealant’s adhesion and curing process.

• Pro Tip: For best results, apply sealant when temperatures are between 10°C and 25°C.

Step 2: Thoroughly Inspect the Roof

Conduct a detailed inspection to identify all potential leak sources, including seams, joints, fastener heads, and flashing. Mark these areas so you don’t miss any spots during the repair.

• Pro Tip: Look for signs of corrosion or visible rust, as these are common points of failure.

Step 3: Clean the Roof Surface Meticulously

A sealant will only bond to a clean surface. Remove all dirt, debris, rust, oil, and old sealant residue with a broom or pressure washer. For stubborn rust, use a wire brush and sandpaper to get down to bare metal.

• Pro Tip: The roof must be completely dry before you apply any product.

Step 4: Prepare the Surface for Sealant

Prepare the surface to ensure maximum adhesion. For any rusty areas, apply a rust converter or a primer. For clean, non-rusted metal, a metal etch primer will significantly improve the bond.

• Pro Tip: Always check that your primer and sealant are compatible before you start.

Step 5: Select the Appropriate Sealant

Choose a high-quality waterproof sealant for roofing that’s flexible and compatible with your surfaces. Products like silicone, polyurethane, or a heavy-duty bituminous sealant are all great options.

• Pro Tip: Ensure your sealant is suited to local environmental conditions, particularly the amount of thermal movement the roof will experience.

Step 6: Apply Sealant Correctly

For seams, joints, and fasteners, use a caulking gun for precise application. Apply a generous, even bead and ensure there are no gaps or air voids.

• Pro Tip: When sealing overlap seams, always work from the bottom up to prevent water from getting trapped.

Step 7: Allow Proper Curing Time

Follow the manufacturer’s instructions for curing time, as this is essential for a durable seal. This process typically requires at least 24 hours of dry conditions.

• Pro Tip: Avoid all foot traffic or water exposure during the curing process to ensure the sealant sets correctly.

Step 8: Inspect and Maintain

After the sealant has fully cured, perform biannual inspections, or after any severe weather, to check for signs of cracking, shrinking, or peeling. A quick touch-up can prevent a larger problem down the line.

• Pro Tip: Remember to check local building codes, durability standards, and how they impact your roofing projects and warranties.

Soudal Sealants vs Competitors 

Your reputation is built on getting the job done right the first time. When sealing a metal roof, a professional-grade product can make the difference between a long-lasting fix and a costly call-back. This product comparison chart shows how Soudal sealants stack up against the competition.

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 Roofing & Gutter Silicone for the professional-grade solution.

With its superior elasticity, non-corrosive formula, and resistance to the Australian sun, 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.

Shop the Soudal Roofing & Gutter Silicone today and secure a lasting fix.