6 Best Rubber Grommets For Sealing Fastener Penetrations

Waterproofing a roof isn’t just about the panels or shingles; it’s about the integrity of every single fastener penetration. When a screw pierces the substrate, the rubber grommet becomes the primary line of defense against moisture intrusion and roof leaks. Choosing the wrong sealing washer or installing one improperly turns a high-quality metal roof into a potential liability. Reliability starts with understanding the specific material and environmental demands placed on these small but critical components.

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Sealtite ZXL Kwikseal II Woodbinder: Best Overall

The Sealtite ZXL stands out because it combines a proprietary head design with a robust EPDM washer that handles thermal expansion exceptionally well. When installing metal panels over wood purlins, the expansion and contraction cycles can cause screws to back out or shear the seal. This fastener compensates for that movement, maintaining a watertight bond even after years of fluctuating temperatures.

The oversized, molded-on head covers the washer completely, shielding the rubber from direct UV degradation. This is a critical feature, as harsh sunlight is the primary cause of premature EPDM dry rot. In high-wind zones where the roof plane experiences constant vibration, the added structural stability of the ZXL head prevents the washer from “walking” out from under the fastener.

Ultimately, this is the go-to choice for residential metal roofing where longevity is the priority. It balances ease of installation with long-term weatherproofing, making it a reliable choice for professional crews and serious DIYers alike.

ITW Buildex ZAC Self-Drilling Screws: Top Pro Pick

ITW Buildex ZAC screws are engineered for high-performance steel-to-steel applications, making them a staple on commercial job sites. The standout feature here is the ZAM alloy coating, which provides superior corrosion resistance compared to standard zinc-plated fasteners. If the job involves fastening to steel purlins in a coastal environment, these are virtually non-negotiable.

The sealing grommet on these screws is specifically matched to the drill-point performance. Because self-drilling screws can generate high friction heat during installation, the grommets are formulated to resist melting or deforming during the drive. This prevents the “over-tightening” issue that often leads to cracked rubber and failed seals.

Professional contractors prefer these because they save time and provide documented consistency. When the success of a building envelope depends on thousands of individual penetrations, the predictability of the ZAC system offers legitimate peace of mind.

Levi’s Fastgrip EPDM Bonded Washer: Best Bulk Buy

Levi’s Fastgrip washers are the standard for high-volume jobs where budget control is as important as performance. These EPDM-to-steel bonded washers provide a consistent, reliable seal at a fraction of the cost of premium, integrated head systems. They are the workhorse of the industry for agricultural and secondary structures.

While they lack the integrated UV-shielding hoods found on more expensive fasteners, they perform admirably when installed correctly on flat surfaces. The EPDM rubber remains flexible across a wide temperature range, ensuring the seal doesn’t become brittle in freezing winters. For large-scale pole barns or storage sheds, these washers offer the best balance of cost and durability.

When using these in bulk, pay close attention to the seating of the fastener. Because the washer is exposed, it requires the fastener to be driven perfectly perpendicular to the metal surface. Any angle in the driving process will result in a compromised seal regardless of how good the rubber quality is.

TFC BLAZER-3 Drill Screw: For Heavy-Duty Steel

The TFC BLAZER-3 is built for the rigors of heavy-gauge steel applications where standard screws often fail. The drill point is aggressive, piercing thick steel quickly without the need for excessive downward pressure. This speed is vital for maintaining control and preventing the washer from being crushed before the fastener is fully seated.

These fasteners are frequently used in commercial roofing projects where thick-wall purlins are common. The sealing washer is oversized to account for the larger drill bit diameter required for these specialized screws. This ensures that the footprint of the seal is wide enough to cover the burrs often left behind after drilling through heavier steel.

For projects involving thicker purlins or structural steel, avoid the temptation to use standard residential fasteners. The BLAZER-3 provides the necessary clearance and mechanical integrity to ensure the seal isn’t compromised by the jagged edges of heavy-gauge penetrations.

EPDM Sealing Washers: Best for Custom Fasteners

Sometimes, the standard fastener length or style just doesn’t match the specific demands of a custom flashing detail. In these scenarios, sourcing high-quality EPDM sealing washers separately allows for precision customization. EPDM, or Ethylene Propylene Diene Monomer, is the industry standard for exterior sealing due to its exceptional resistance to ozone and UV rays.

When buying these for custom applications, focus on the rubber durometer, or hardness rating. A shore hardness of 60-70 is ideal for most roofing applications, as it provides enough flexibility to conform to the metal ribs while remaining rigid enough to withstand compression. Ensure the washer has a galvanized or stainless steel backing to prevent the rubber from deforming under the screw head.

This approach is best for roof penetrations, pipe flashings, or custom sheet metal work where proprietary screws aren’t available. It keeps the seal independent of the fastener, which can be an advantage when dealing with unique substrate thicknesses.

Neoprene Bonded Sealing Washers: Best for Oil/UV

Neoprene is an excellent alternative to EPDM, particularly in environments where oil, grease, or chemical exposure is a concern. While EPDM is better for general exterior weatherproofing, Neoprene maintains better structural integrity in industrial settings, such as near HVAC exhaust fans or ventilation units where petroleum-based residue may settle on the roof.

Neoprene is slightly more resistant to physical abrasion and extreme temperature spikes. If the roof installation site is subject to heavy industrial soot or high-heat exhaust, Neoprene will outlast EPDM by preventing the chemical breakdown that leads to sticky, failing seals. Always verify the chemical compatibility of the environment before choosing this over standard EPDM.

Like other sealing materials, Neoprene is prone to UV degradation over long periods. If installing these in an open, sun-exposed area, prioritize a fastener head that provides at least partial coverage for the rubber.

EPDM vs. Neoprene: Choosing the Right Gasket

Choosing between EPDM and Neoprene comes down to the environmental profile of the roof. EPDM is the clear winner for almost all standard residential and light-commercial roofs due to its superior outdoor weathering capabilities. It handles freezing, thawing, and intense sun exposure without losing its elasticity.

Neoprene occupies a specific niche for roofs with industrial exhaust or chemical risks. It is less common in residential applications, but essential for commercial jobs where the roof environment is compromised by heavy machinery. Using the wrong material can lead to the rubber becoming “gummy” or cracking within a few years of exposure to local atmospheric chemicals.

• EPDM: Superior UV resistance, excellent elasticity, ideal for general roofing.
• Neoprene: Resistant to oils and greases, better for industrial exhaust environments.
• Check the Spec: Always refer to the manufacturer’s technical data sheet for the specific chemical resistance rating if the roof is near an industrial site.

How to Properly Install Sealing Fasteners

Proper installation is the single most important factor in preventing leaks. The goal is to compress the rubber washer just enough to create a firm seal, but not so much that the rubber splits or “mushrooms” out from under the fastener head. A properly installed washer should show a slight, uniform bulge around the perimeter of the screw head.

Use an adjustable clutch drill, not an impact driver, whenever possible. An impact driver can apply too much torque, causing the fastener to strip the substrate or damage the washer before the operator realizes it. Set the torque to a low level and finish the final turn by hand if the roof material is thin or delicate.

Always drive the screw perpendicular to the panel surface. If the screw enters at an angle, the washer will not seat evenly, leaving a gap on one side that will eventually channel water into the penetration. Take your time to ensure the tool is level; it is significantly faster to drive a screw straight than to fix a leak later.

Common Mistakes When Sealing Roof Fasteners

The most common mistake is over-tightening. It is tempting to drive the screw as deep as possible to ensure “tightness,” but this almost always results in a ruined gasket. A crushed washer loses its ability to flex and recover during thermal expansion, which is the exact moment the roof needs it to be most effective.

Another frequent error is failing to clean the area after drilling. Small metal shavings, often called “swarf,” left under the washer will inevitably rust and create a leak point. Always clear the debris from the hole before fully seating the fastener.

Finally, do not reuse fasteners. Once a sealing washer has been compressed, the rubber takes a permanent set. Removing and reinstalling a screw means the washer will no longer have the memory or the compression needed to form a new, reliable seal.

Checking Torque: Key to a Long-Lasting Seal

Consistent torque is the secret to a professional-grade roof installation. Many contractors use the “look” of the washer to determine when to stop, but this is subjective and prone to error. Relying on a torque-limiting attachment or the clutch setting on a high-quality drill provides a standardized result across every fastener on the roof.

If you are working with varying substrate thicknesses, you must adjust your torque settings accordingly. Driving into thin-gauge metal requires less torque than driving into a thick structural steel beam. Failure to adjust will result in under-compressed washers on the steel and destroyed washers on the lighter panels.

Test your settings on a scrap piece of metal that matches the gauge and material of the roof before starting the main work. If the rubber is bulging evenly and is firm to the touch, you have the right setting. A consistent, well-sealed roof is rarely the result of luck; it is the result of disciplined, repeatable installation habits.

Achieving a watertight roof depends entirely on the small details that remain hidden once the job is finished. By selecting the correct washer material for your specific climate and ensuring proper installation technique, you can prevent the vast majority of common roof leaks. Always prioritize the integrity of the fastener seal, as it is the most frequent point of failure on any metal roofing system.