Bonding Washer, or Bonded Washers, is a combination of Flat Washer and EPDM Rubber Washer. With the Flat Washer facing on top, the EPDM Washer seals the gap between the screw and object.

The design of the Bonding Washers is to prevent water from entering where the fastener is sealed.

Bonding Washers are placed onto a screw and fastened down onto an object.


Since the force of the screw is distributed evenly onto the Bonding Washer, the EPDM Washer will expand inward and outward to create a nice seal for any uncovered gaps.

The EPDM Washer on the Bonding Washer is a low-cost weather resistant rubber and can withstand up to 275°F.

Although EPDM rubbers are the most common, there are other types of rubber also made for similar purposes, such as neoprene and silicone.

Bonding Washers are mostly made to pair up with Roofing Screws.


They are installed before the color coating process to have the same coating as the screw.

The installation for screws with Bonding Washer is not as easy as it seems.

The incorrect installations of the screw will give insufficient or excessive tightening to the Bonding Washer.

This may cause water leakage around the EPDM or damage to the EPDM and create gaps between the objects.

The correct installation should push the EPDM outward and inward to fully cover the surface of the Flat Washer and the screw threads on the inside.


Most Bonding Washers are made with zinc coatings to prevent corrosion. However, a good amount of Bonding Washer will be color coated again in the process to greatly improve the resistance.




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