Backer rods are a simple solution to help avoid major construction issues that can pop up after time. Backer rods are flexible lengths of foam that are used to insulate, cushion and be a backing in a joint, foundation, gap or crack. Backer rods are excellent at controlling the amount of sealant used or the depth of the sealant in a gap. The backer rod most importantly acts as a bond breaker, preventing what is referred to as three sided adhesion or three point bonding. This is when the sealant improperly adhereds to the bottom and sides of the joint, restricting movement.

Since voids vary in shape and width, selecting a backer rod in the correct size is essential to controlling sealant depth. Backer rod comes in several variations and diameters as well as in three main types, closed cell, open cell, and a hybrid bi-cellular version that has closed outer cells and open interior cells. Each one of these types of backer rod has its own niche that it thrives in. Some applications require closed cell material that won’t absorb moisture, others seal best with open cell foam that is highly compressible and will fill irregular joints more evenly. It’s important to understand that cell structure makes a critical difference when it comes to irregular joint application, the desired flexibility in the joint, or sealant being used.

Benefits of Backer Rods

  • Increases elasticity in the joint sealant
  • Reduces caulk consumption by controlling sealant depth
  • Forces adhesive into contact with the sides of the joint creating an hour-glass shape for a superior bond
  • Creates a “bond-breaker” which allows the joint to be easily cleaned and refilled as needed over time
  • Provides a stable chinking or caulking surface
  • Compresses to fit a wide variety of gaps
  • Can be used on exterior or interior surfaces

Types of Armacell Backer Rods

FillPro™ standard backer rod is an extruded round, closed-cell, low density polyethylene foam material with a skin-like outer texture. Standard backer rod is non-absorbent, flexible and compressible allowing for easy installation in joints as a backup material for sealants. Standard backer rod is 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. The closed cell backer rod is best in horizontal or flat joints as its closed cell structure keeps moisture from wicking through it. It is much more robust which can make installation more challenging when compressing the backer rod into joints.

FillPro™ Hot Rod XL backer rod is an extruded round, closed-cell, low-density polyethylene 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. Hot Rod XL backer rod is a backup 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.

FillPro™open-cell backer rod is pliable open cell polyurethane 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. 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 sealants including silicone and rubber asphalt. Using a permeable backer rod will allow the sealant to react with atmospheric moisture to cure on the interior side. Open-cell backer rod should not be used in flat or horizontal joints that can have water pooling on them as they can wick moisture to the underside of the sealant. Open-cell backer rods may not be ideal for sealants that are susceptible to bubbling of air escaping the backer rod material.  

FillPro™ soft type backer rod is a pliable bi-cellular polyethylene 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 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, FillPro Soft Type is ideal in irregular joint applications especially 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. The hybrid style backer rod is easy to install with an internal open cell structure that can compress easily.

Types of Sealants

Sealant material selection is critical to a successful joint expansion installation, with proper adhesion to substrates being the most important element in an installer or contractor’s selection process. Commonly a sealant is recommended by the contractor based on the substrate materials. Other considerations can be the type of application being completed, possible environmental factors or any applicable site or industry legislation requirements. Some of the most commonly used field molded sealants are made of polyurethanes and silicones. Others less frequently used are latex, acrylic, butyls, polysulfides, elastomerics, or prefabricated sealants like gaskets, strip seals and compression systems. All sealants have a risk of failure such as cohesion failure, cracking, staining or substrate failure, but the use of a proper backer rod as a filler can help eliminate these concerns.

No matter the application or sealant being used, Armacell offers an extensive collection of backer rod materials with the largest range of sizes in the market. Ensure your next project is a success by properly sealing voids and using Armacell’s backer rods.

For more information on the FillPro family of backer rods, visit the sealant accessories page here.