Cladding Joints and Sealant Performance

OSI proper fillet sealant bead


To understand how sealants perform in a joint, it’s important to understand how the cladding itself performs — whether vinyl, fiber cement, engineered wood, stucco, stone or other material And cladding performance is highly influenced by three factors: movement, joint design and fastening.


  • Movement. This varies by cladding transition. All cladding moves. Manufacturers anticipate this and recommend a gap size between dissimilar materials that accommodates that movement.


  • Joint design. This also varies by cladding transition, as well as characteristics such as cladding depth, design and movement. For example, a transition between fiber cladding (very stable and little movement), and stone (broader movement characteristics), will require a control joint with backer material.


  • Fastening. This also varies by cladding type, whether securing cladding to the structural framing or concrete/masonry wall systems. The right fastening allows the acceptable amount of movement for best cladding and sealant performance.


Sealant Performance

To understand how sealant performs, it’s important to understand how it moves and adheres.

  • Movement. All sealant, like all cladding, is designed to move, and some sealants move more (or less) than others. When working with a range of different cladding types, choose a sealant that provides movement versatility to allow for the many variations in cladding movement capability.


  • Adhesion. Surface-to-surface contact is critical to sealant performance. Pay attention to things like the depth of a control joint or the exposed surface area between trim and lap siding joint. If there is not enough surface contact between sealant and substrate, it can hinder the ability of the sealant to hold a bond over time.



OSI fillet bead sealant siding installation


Sealant Joints

Knowing how to apply the two types of sealant joints for cladding applications — Fillet joints and Control joints — can help maintain good sealant performance.

  • Fillet Joint. Triangle-shaped bead that “fills in” the corner formed by two surfaces meeting at a right angle, such as cladding and trim.


  • Control Joint. Fills the area between two non-perpendicular surfaces such as a window frame and window trim. Backer rod must be inserted in the gap prior to sealing.


Sealant Application

For either type of sealant joint:

  • When “gunning” sealant into a joint, apply consistent pressure sufficient to create at least ¼” of surface contact on each side of the joint for good two-sided adhesion. This will also provide an adequate amount of sealant to withstand designed movement.


  • Do not tool or smear the bead. Tooling or smearing will reduce the sealants ability to withstand joint movement, causing premature joint failure.



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