EPDM Bonded Washers: what they’re for (and why they work so well)
EPDM bonded washers (also called bonded sealing washers) are made for one job: stopping water ingress around a fixing. They do this by combining a metal washer with a bonded EPDM rubber sealing ring. When you tighten the fixing, the metal spreads the load while the EPDM compresses to create a dependable seal. The result is a neat, professional finish that holds up outside, even when the job is exposed to rain, movement and vibration.
You’ll see EPDM bonded washers used all the time on roofing and cladding sheets, flashings, outdoor brackets, signage, timber projects, fencing, and any general installation where you’re fastening through a panel and don’t want moisture tracking down the shank of the screw or bolt.
What EPDM bonded washers are good for
- Weatherproof sealing around screws and bolts on external installs
- Roofing and cladding (box profile, corrugated sheets, composite panels, flashings)
- Outdoor structures like pergolas, fencing, gates, brackets and fixtures
- Reducing loosening from vibration by maintaining compression at the fixing point
- Protecting coatings and painted surfaces by spreading load and reducing point pressure
- Cleaner installs where you want the sealing to be built in, not an afterthought
Who uses EPDM Bonded Washers
These are a staple for trade buyers who fit, fix, and maintain outdoor installations:
- Roofing and cladding installers
- Builders, joiners and general trades
- Fabricators and metalworkers
- Maintenance teams, facilities and site managers
- Purchasing managers buying consistent, repeat-use consumables for crews
If you’re ordering for site, the big win is consistency: the same washer, same seal, job after job, without having to mess about with extra sealants unless the spec demands it.
Why buy EPDM bonded washers from Fixabolt
Trade buyers usually care about a few things: correct sizes, reliable stock, and pricing that makes sense when you’re ordering in quantity. That’s exactly how we run Fixabolt.
- Trade-friendly pricing and bulk breaks to suit repeat orders
- Clear sizing so you can match the washer properly to the fixing and application
- Fast UK delivery and dependable fulfilment
- Straightforward service from a specialist fixings business (no fluff, just the right parts)
If you’re buying for a team, it’s also easier when you can standardise your washer sizes across common screw/bolt diameters and keep spares in the van.
EPDM Bonded Washers FAQ
What is an EPDM bonded washer?
It’s a metal washer with an EPDM rubber sealing ring bonded to it. When tightened under a screw head or nut, the EPDM compresses to form a seal while the metal supports the load.
What are EPDM bonded washers used for?
Mostly for water sealing around fixings in outdoor or exposed applications, such as roofing and cladding sheets, flashings, brackets, and general external installations.
Are EPDM bonded washers waterproof?
They’re designed to create a water-resistant seal when installed correctly and tightened to the right compression. Like any seal, performance depends on correct sizing, a clean seating surface, and not over- or under-tightening.
Do I need sealant as well as a bonded washer?
Often, no. In many standard installs a bonded washer is enough on its own. For higher-risk details (overlaps, penetrations, unusual surfaces, or where the spec requires it), you may still use sealant or additional sealing methods.
How do I choose the right size bonded washer?
Match the inner diameter to your fixing diameter so it seats properly, and choose an outer diameter that spreads the load suitably for the material you’re fixing through (thin sheet usually benefits from a larger OD).
Can EPDM bonded washers be used with Tek/self-drilling screws?
Yes, they’re commonly paired with self-drilling screws for roofing and cladding work. The key is choosing a washer with the right inner diameter for the screw and a suitable outer diameter for the sheet.
What’s the benefit of EPDM vs other rubber types?
EPDM is widely used outdoors because it handles weathering and moisture well and stays flexible over time. That’s why it’s a go-to for roofing, cladding, and external fixings.
Can you over-tighten an EPDM bonded washer?
Yes. Over-tightening can over-compress the EPDM, cause it to squeeze out, or distort the washer, which can reduce sealing performance. Tighten to firm compression so the rubber seals, without crushing it flat.
Are these suitable for stainless steel fixings?
Yes. EPDM bonded washers are commonly used alongside stainless fixings for outdoor corrosion resistance. Just make sure the washer’s metal backing suits the environment you’re installing in.
