Backer rods are foam rods used to fill joints between building materials. They add stability, accuracy, and save time. Open cell rods are best for indoor use, while closed cell rods are better for outdoor use. They allow building materials to move and flex based on environmental factors. They are not essential but are useful. Alternative products include elastomeric caulks.
A butt rod is a small foam rod or string used to fill joints between tiles or other pieces of building material. Builders and contractors often use this tool to initially get into grooves or cracks and then apply grout, sealant, or filler around it. The rod adds stability, accuracy, and generally saves time. There are typically two types of backer rods, open cell and closed cell; they can often be used interchangeably, although open versions tend to be better for indoors where there isn’t a lot of humidity. Decks, patios and walkways that are outdoors most commonly use closed cell rods as a way to add insulation and waterproofing. Either way these tools aren’t usually essential to any application, but they can improve the look and durability of many different projects.
primary uses
Builders use this type of foam bar for a number of different building projects, but almost always in the context of filling gaps where materials join together. They are most commonly used in tile and flooring, but can also be found in decorative wall paneling, window sealing, stonework, and countertops. The main idea is to use foam to fill most of the void in a joint so that caulking or cracking material, a grout-like sealant, can be applied to complete the fill and create an airtight, waterproof seal. . The rods also add precision and firmness which can give a more finished look to the final result.
Rods are generally available in a wide range of diameters from 1/4 inch (6.35 mm) to 4 inches (101.6 mm) or more. Some retailers sell them to order or they may come in small, pre-cut packets. Large distributors or busy contractors often buy their rods in bulk, often in 1,650-foot (502.92-meter) rolls. Different specifications are usually best for different projects, so the type of rod needed for tile flooring in a bathroom may be different than what is needed for kitchen counters or stone walkways.
Open cell rods
Rods also typically come in two main types, namely open cell and closed cell. The distinction usually has to do with the density of the foam. In an open cell rod, the material is usually airy and breathable, while it is much denser in a “closed” version.
Open cell products tend to be the easiest to install because they are soft and very flexible. The large diameter pieces can be compressed to fit gaps that vary in thickness in some areas, meaning this style is also more universal; can be compressed to fit a range of different sizes and projects. However, open cell products are generally only designed to be used indoors. This type of material is not a good insulator and does not typically repel water.
Closed cell versions
Rods made with closed cell foam are denser and firmer, making them harder to bend and maneuver, but also more suited to heavier, outdoor environments. The closed cell version repels moisture, provides a stable finish to the crack and can be fixed in place with a spray adhesive. It is commonly used for smaller joints in the range of 1/4 to 3/8 inch (6.35 to 9.52 mm) and has a higher insulating value than open cell forms.
The biggest benefits
Rods of both varieties allow building materials to move, bend and flex based on the environmental factors they are exposed to, such as humidity, heat, cold, wind and exposure to ultraviolet light. In most cases, folding materials are flexible sealants that will remain flexible throughout their useful life. They will attach to the building materials, but not the support rod. For this reason, the foam is also called a bond breaker.
There are only a few scenarios where backer rods are essential, but they are almost always very useful. Builders can often use caulking or cracking material to fill the entire gap, but the “cure” or dry time for large quantities of these products would be a number of days or weeks, depending on the size of the gap. Things are much faster with the rod and often the results are more reliable as well.
Alternative products
Other sealing materials besides rods can be used to fill gaps, including elastomeric products and other flexible caulking products. Elastomeric caulks are able to bend, flex, expand, contract and stretch as needed while maintaining a tight bond and airtight seal. These caulks and sealants are capable of stretching to 200% or more of their original shape and size and are often paintable with acrylic latex paints as well.
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