6 Best Rubber Washers For Secondary Sealing Pros Use

The integrity of a roof often hinges on the smallest components, and nowhere is that more true than with secondary sealing washers. When a fastener penetrates a metal panel, the hole becomes a potential entry point for water, wind, and debris. Choosing the right rubber washer is not just about grabbing the first bag off the hardware store shelf; it is about matching material elasticity and UV resistance to the specific demands of the climate and the structure. A failure here rarely shows up immediately, often manifesting as a slow, corrosive leak that destroys decking long before a stain appears on the ceiling.

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Sealtite ZXL Washer: The Pro’s Go-To Choice

The Sealtite ZXL washer is widely considered the industry standard for high-end metal roofing applications. It features a unique design that encapsulates the fastener head, providing an extra layer of protection against the elements.

This choice is ideal for contractors dealing with high-wind zones where lateral movement of panels is expected. The proprietary rubber blend maintains its memory, meaning it expands and contracts without losing its seal even as temperatures fluctuate wildly throughout the day.

Avoid using these on budget-grade panels where the metal gauge is too thin to support the washer’s compression profile. When the metal is too soft, the washer will deform rather than seal, leading to an inevitable drip. Always prioritize this washer when the job requires a lifetime warranty-grade seal.

Buildex Climaseal: Top Pick for Metal Roofs

Buildex Climaseal washers are engineered specifically to pair with long-lasting metal coating systems. They are designed to sit flush against the panel rib, preventing the “crush” effect that often leads to cracked rubber over time.

These washers excel in environments where salt spray or high humidity is a factor. Because the washer and the fastener coating are tested as a single system, the risk of galvanic corrosion—where dissimilar metals react and degrade—is virtually eliminated.

For those installing exposed fastener roofs, the shape of the washer provides a consistent seal even if the driver bit tilts slightly during installation. When in doubt, use a system-matched washer to ensure the manufacturer’s warranty remains intact.

Leland Master Seal: Best for Wood Substrates

The Leland Master Seal is a heavy-duty option designed for the unique challenges of fastening metal to wood. Because wood substrates expand and contract significantly with moisture, the fastener itself often experiences micro-movements.

This washer is thicker and more compliant than standard neoprene alternatives, allowing it to “track” with the fastener as the wood breathes. It prevents the common issue of the rubber backing out or shearing off due to the constant vibration of wind loads on wooden purlins.

If the project involves older, weathered lumber, this washer provides the necessary surface area to bridge gaps in the timber. It remains the most reliable choice for barn roofs and pole buildings.

Tru-Grip Bonded Washer: For Corrugated Panels

Tru-Grip washers are purpose-built for the challenging geometry of corrugated roofing. The profile of a corrugated panel creates a steep angle for the fastener to land on, which often causes standard flat washers to seal on only one side.

These bonded washers provide a flexible, concave profile that conforms to the wave of the metal. This ensures that the pressure is distributed evenly around the entire circumference of the hole, rather than being concentrated at a single point.

For installers who struggle with over-driving fasteners on corrugated ridges, this washer acts as a visual and physical indicator. Look for the specific curvature that matches the rib profile of the panel being installed.

Hillman Group Neoprene: Value Pick for Bulk Use

For smaller residential projects or sheds where the cost-to-performance ratio is critical, the Hillman Group neoprene washers are a solid, accessible choice. They offer decent UV resistance and provide a functional seal for standard 26 or 29-gauge metal.

These are best utilized in low-risk, low-slope applications where the roof is easily accessible for future maintenance. They lack the high-end engineered memory of premium brands, so expect them to harden slightly faster in extreme desert heat.

Keep them away from direct chemical exposure or harsh industrial environments. These represent the best balance of cost and performance for DIYers tackling backyard structures.

Bolt Dropper EPDM: Best Stainless Steel Option

When a project calls for stainless steel fasteners—especially in coastal areas—the Bolt Dropper EPDM washers are the only responsible choice. Stainless steel is incredibly hard, and using a soft or cheap washer will cause the fastener to “eat” the rubber during the tightening process.

EPDM (Ethylene Propylene Diene Monomer) is the gold standard for long-term outdoor exposure. It does not crack under intense UV rays and remains flexible for decades, making it the perfect partner for 304 or 316-grade stainless screws.

If the job is located within five miles of the ocean, using anything less than a high-quality EPDM/stainless combination is a liability. Always ensure the washer is rated for the same lifespan as the stainless steel fastener.

EPDM vs. Neoprene: Which Seal is Right for You?

Understanding the chemistry of these two materials is essential for long-term roofing success. EPDM is a synthetic rubber known for its superior heat, ozone, and weather resistance, while neoprene is a synthetic polymer that offers better resistance to oil and chemicals.

EPDM is the clear winner for roofing because it resists oxidation and UV degradation, the two primary killers of roof seals. Neoprene may be cheaper, but it will eventually lose its elasticity and become brittle, leading to leaks within a decade.

If the roof is in an area with high sunlight exposure, spec EPDM every time. Choose based on the environment, not the price tag.

How to Properly Tighten for a Watertight Seal

The most common failure in roof installation is over-tightening. If the rubber washer is bulging out significantly from under the metal head, the seal has already been compromised by excessive pressure.

The goal is to achieve a snug fit where the washer is slightly compressed—just enough to bulge slightly—but not enough to tear or permanently deform. Using an impact driver with a torque-limiting clutch is the most effective way to maintain this consistency across a whole roof.

If the washer is deformed, it creates a “cup” that collects water, accelerating corrosion around the hole. A light touch is always superior to an over-tightened disaster.

Match Your Washer to Your Fastener and Panel

Matching the washer diameter to the fastener head is a non-negotiable rule. A washer that is too small for the fastener head will offer no protection, while one that is too large can trap moisture under the edges.

Consider the panel’s expansion coefficient; large-format metal panels move significantly more than smaller sections. Using a slightly larger, more compliant EPDM washer allows for that movement without breaking the seal.

Always account for the fastener length as well. If the screw is too long, the washer will never be properly compressed; if it is too short, the rubber may be over-compressed to reach the wood. Measure the panel and purlin thickness precisely before selecting your hardware.

Galvanized vs. Stainless Steel: Climate Matters

The compatibility between the fastener, the washer, and the metal panel is a matter of basic chemistry. Galvanized fasteners paired with aluminum or certain modern coated panels can lead to rapid oxidation of the steel.

Inland, standard galvanized fasteners with EPDM washers are often sufficient for the service life of the roof. However, in regions with heavy acid rain, salt spray, or high moisture, stainless steel is the only way to prevent premature fastener failure.

Ignoring these nuances usually results in “weeping” fasteners where rust stains appear around the washer after only a few seasons. When in doubt, step up to the higher-grade fastener and washer combo to avoid costly call-backs.

Selecting the right rubber washer is a small investment that dictates the long-term success of the entire roofing system. By prioritizing material quality and ensuring proper installation technique, the integrity of the envelope remains secure against even the harshest environmental variables.