Jump to main content

Fillet Beads Keep Mother Nature Cornered

Keeping Mother Nature out of your building envelope requires knowing how its many components function and how to use them. A simple bead of sealant, for example, can be the critical first line of defense in vulnerable areas such as right-angle corners. Here, Paul Majka, OSI Application Engineer, takes us on a deep dive into the fillet bead.

2 min.
osi article adhesives stage

What are the most common mistakes people make with fillet beads?

Many people are not aware how critical the proper application is for a fillet bead. And the three most common mistakes they make are 1) too small a bead, 2) unbalanced beads and 3) over-tooled beads. To effectively seal a right-angle corner, a fillet bead has to be at least ⅜” and balanced evenly on each face of the angle. Make the bead to small or apply too much sealant to one side or the other and you create a weak seal. And over-tooling simply removes too much sealant from the joint and weakens its ability to perform.

When do you use a fillet bead?

You use a fillet bead in a fillet joint, which is formed when two surfaces come together to form a right angle. Sealant is applied to this joint to join the two surfaces in a triangular shape.

What makes it a good solution for right angle joints?

It’s actually the only solution for right angle joint designs. When applied correctly, a fillet bead will withstand the demands of joint movement and adhesion against the cyclical pressures of sun, wind, water, snow and ice. It becomes the primary seal to protect against these elements and provide durability and longevity for the building envelope.

How do you know you’re looking at a good fillet bead?

A fillet bead is triangular in shape and should be applied to a specific dimension—3/8” wide, ¼” deep on both sides of the joint and 1/8” inch center depth.

us osi main image 2 fillet bead

What's the best way to apply a fillet bead?

Cut the sealant cartridge or tube nozzle at a 45°-degree angle. The nozzle should be cut to expose a 3/8” inch opening. The nozzle is then centered in the right-angle joint and sealant is dispensed over the gap and against both surfaces. It’s important that the dispensing of the sealant and movement of the gun are balanced to apply a consistent bead along the length of the joint.

How do weather conditions affect it?

If sealant is applied correctly to the fillet joint, the sealant will perform no matter how severe the weather conditions. It will deliver the required performance against extensive UV, water and wind exposures sustain joint movement capability needed.

Related Products

  • osi h2u window door siding trim sealant white 10oz cartridge

    OSI® H2U

    Sealant for window, door & siding applications

  • osi quad max 9.5oz cartridge


    Sealant for window, door & siding applications

  • packshot product us osi sealants quad

    OSI® QUAD®

    Sealant for window, door & siding applications


Recent Articles

  • Choosing A Construction Sealant Technology

    It’s a great time to consider a new sealant formulation. Compare new and old technologies. 

  • North Georgia Tackles Big Challenges with OSI

    Find out how partnering with OSI helps Ted Kirk protect his company's reputation. 

  • Technical Bulletin: Sealant Bubbling

    Learn how to prevent and fix the occurrence of sealant bubbling.