Installation contractors know the importance of the backer rod during projects. Yet many ask, what is the reason for backer rods in the application of sealants? Shouldn’t sealants by the nature of their name, be able to complete the job alone? Not always.

When used as a "backing" in expansion joints or cracks to help control the amount of sealant used or the depth of the sealant in the gap, the backer rod serves two primary functions. First, backer rod acts as a bond breaker, meaning it allows the sealant to adhere to the walls of the joint and not the bottom. This allows the sealant to expand and contract without releasing it from the sides, maintaining a tight seal. Second, backer rods help fill in gaps between the surfaces, save on sealant, and create a depth that is the right size for an effective bond. Even though backer rods are not considered a major component of a building, their contribution also helps achieve the sealant “hourglass” profile and prevent the detrimental 3-sided adhesion for moving joints. These innovative, foam rods used during construction are essential and necessary to a project’s success based on these reasons.

What is a Backer Rod?

Backer rods are flexible lengths of foam that come in many shapes, sizes, diameters, and types for optimal fitting of the joint being sealed. Besides size and shape, an important attribute is the foam cell structure types: closed-cell, open-cell, and bi-cellular. Cell structure makes a critical difference when it comes to irregular joint application, the desired flexibility in the joint, or sealant being used. Some applications require closed-cell back-up material that won’t absorb moisture, others seal best with open-cell foam that is highly compressible and will fill irregular joints more evenly. No matter your application, Armacell offers the most extensive collection of backup materials and the largest range of sizes on the market today. 

ArmaCompTM FillPro Standard Backer Rod is an extruded round, closed-cell, low density polyethylene (PE) foam material with a skin-like outer texture. The Standard backer rod is non-absorbent, flexible and compressible allowing for easy installation. Plus, it's recommended for glazing installations, window and door applications, expansion joints, log construction, pavement joints or repairs and precast concrete joints and copings. It’s compatible with most cold-applied sealants. It is available in spools with diameters ranging from ¼” to 1¼” and in 6' lengths for sizes larger than 1½”.

ArmaCompTM FillPro Hot Rod XL Backer Rod is an extruded round, closed-cell, low-density PE foam material which has been specially crosslinked to withstand temperatures in excess of 400°F (204°C). It is chemically inert and will resist oil, gasoline and most other solvents. The material will not stain, absorb moisture, nor adhere to sealant materials and is non-exuding. The Hot Rod XL backer Rod is a back-up material for most hot-pour sealants used to fill contraction and expansion joints of concrete highways, runways, driveways, and parking lots. It’s compatible with most rubber-asphalt and coal tar-rubber polymer thermoplastic compounds.

ArmaCompTM FillPro Soft Type Backer Rod is a pliable bi-cellular PE foam material used for filling irregular joints. It is chemically inert and will resist oil, gasoline and most other solvents. The material will not stain or adhere to sealant materials, and it is non-exuding. Its unique construction is highly compressible but has a closed-cell outer skin to resist moisture. Particularly suited for specialty applications where standard backer rods are not appropriate, the FillPro Soft Type is ideal in irregular joint applications particularly where self-leveling, flowable sealants are employed. Also recommended with sealants where bubbling concerns are critical. An excellent all-purpose backer rod, it may be used in place of most standard backer rod applications.

ArmaCompTM FillPro Open-Cell Backer Rod is a pliable open-cell polyurethane (PU) foam material used for filling irregular joints. It is chemically inert and will resist oil, gasoline and most other solvents. The material will not stain, or adversely adhere to sealant or caulking materials. The open-cell backer rod is commonly used in expansion and contraction joints, window glazing, curtain wall construction partitions, precast concrete assemblies and copings, parking decks and bridge construction. It’s compatible with virtually all known hot-pour and cold-applied sealant including silicone and rubber asphalt.

For more information on ArmaCompTM FillPro click here.