September 21, 2022

Here’s the Skinny on Joint Fillers & Sealant Backing Materials in New Construction

For our second blog post of September 2022, we offer the skinny on joint fillers and sealant backing materials in new construction. Sealant backing and bond breakers establish sealant depth and prevent detrimental three-sided adhesion. Properly installed sealant backing prevents sealant leakage and creates a proper sealant profile. Sealant backing function ceases once sealant is applied, tooled, and cured. A joint filler is inserted into joints that are deeper than required for the sealant backing and sealant installation. For moving joints the joint filler and sealant backing must be compressible. Sealant backing provides resistance to sealant tooling pressure and helps to attain proper wetting of the substrate when sealant is tooled.


  1. Closed cell sealant backing: primarily a polyethylene foam with a surface skin
    1. Vertical and horizontal joints with one or two component sealants. Approved for use in EIFS applications
    2. Closed cell sealant backing must be no more than 25 to 33% larger than joint width so it remains in compression and in place during sealant installation
    3. Do not rupture the skin of closed cell sealant backing material during installation, this can cause air bubbles in the sealant compromising its ability to perform
  2. Open cell sealant backing: primarily a urethane foam without a skin
    1. Vertical joints utilizing one-component sealants when cure speed is critical.
    2. Double caulk beads in vertical joints for curing of initial (internal) caulk bead
    3. Must be at least 25% larger than joint width so it remains in compression and in place during sealant installation
    4. Not for use in horizontal traffic joints or EIFS applications
  3. Bicellular sealant backing: composed of both open and closed cell polyethylene or polyolefin foam with a surface skin
    1. Recommended for all sealant applications with the exception of applications requiring rapid curing from backside
  4. Bond breaker tape: Self-adhesive polyethylene or teflon material
  5. Backing materials to avoid
    1. A rigid joint filler or sealant backing in joints that will experience movement
    2. Using braided sealant backing to compensate for a joint opening that is too large for the backing material


For more information about our sealants, sealant applications, or questions regarding this blog post, we recommend contacting our Technical Service Department. They can be reached by email at or by phone at (800) 523-6688.


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