Soft Backer Rod – to ensure Excellent Sealant Performance

A Soft Backer Rod is a soft and pliable non-gassing backing material that is inserted into a joint so as to control sealant depth. The Soft Backer Rod creates a backstop that would facilitate proper sealant tooling so as to achieve a quality bond breaker between the backing material and the sealant. One of the advantages of the Soft Backer Rod why it is preferred by installers is the ease of installation. The Soft Backer Rod is also more forgiving when applied to variable sized joints.

Making a selection for the proper backer rod

Backer rods provide three important functions:

-        To control the depth of sealant application

-        To prevent the 3-sided adhesion

-        To achieve the hourglass configuration that is necessary for proper joint design

Backer rods are available in two basic forms;

-        Closed cell

-        Open cell

Closed cell backer rods are generally used for joints that are susceptible to the presence of moisture prior to joint sealing like horizontal joints. The closed sell backer rod is more rigid which allows it to better handle heavier pressure. Closed cell backer rods are classified into 2 types:

-        Standard backer rods – which is suitable for applications that include glazing, windows and doors applications, curtain wall joints, expansion joints, partitions, log constructions, pavement jobs, repairs, precast units and copings.

-        Soft Backer Rod – are suitable for applications where the standard backer rods cannot be used or are not appropriate for the application. Usually, the Soft Backer Rod is applied for irregular joints and when free-flowing and self-leveling sealants are applied.

Open cell backer rods are designed for sealants that are moisture cured. They are typically used for low-modulus, slow-curing and high performing silicone sealants. Open cell backer rods are more appropriate for application in extremely cold temperatures. Applications for the open cell backer rods include expansion and contraction joints, window glazing, curtain wall joints, partitions, pre-cast units and copings, parking decks and bridge constructions.

Comparison between the closed cell and open cell backer rods

There are many interesting similarities and differences between the closed cell and open cell backer rods. Both are common to predominantly used sealants that are available in the market today. Both have the same chemical resistance and are non-staining which means that will not bleed color to the substrates. This characteristic is highly significant when high end materials like marble are used.

Open cell backer rods are more flexible but in terms of rigidity, it must rely on its chemical and physical properties. In the closed cell backer rod, rigidity is the result of the gases that have been trapped in its interior. Open cell backer rods must be compressed by at least 25% though it does not matter if it can be compressed by as much as 75%. In fact, this will allow the installer to use fewer sizes for varying joint widths. In the case of closed cell backer rods, manufacturers do not recommend compression that is more than 25% of its diameter; hence the installer must use several sizes for different joint widths.