Backer rod is used to fill the base of a crack before filling the crack with caulk. it is made of closed cell foam similar to pipe lagging. We sell backer rod in 10m lengths, in a variety of sizes. It performs several tasks:
- It allows the crack to open and close, being very compressible itself, and by keeping the relatively incompressible caulk out of the base of the crack.
- It saves on caulk, by filling some of the volume with cheaper material than caulk.
- It stops the caulk from sticking to the back of the crack, as well as to the sides where you want it. If the caulk is adhered to the sides and back of a crack shear forces will take place that will cause early failure when the crack moves again.
How do I use Backer Rod for Caulking?
In use, select a diameter of backer rod that will fit into the base of the opened out v groove crack. The backer rod will push into the base, keeping the caulk from contacting the back wall of the crack. All cracks should be repaired in this way, where the caulk adheres to the two side surfaces, and not to the back wall. If the caulk were to adhere to the sides and the back of the crack at the same time, then the action of the crack moving will either try to tear the caulk apart, or attempt to open another crack elsewhere if the caulk resists the shear forces.
If your crack is far thinner than the backer rod it can easily be cut down with a sharp knife.
As the crack opens and closes (as it will, it is why the crack appeared in the first place) the backer rod will be compressed easily, and will not cause another crack to open up elsewhere, which would happen if something less compressible was in the bottom of the crack.
A further benefit of backer rod for caulking purposes is that it is cheaper than all caulks, and far cheaper than the best caulks, such as 3M 5200, and so saves money and caulk.
We sell backer Rod manufactured by Everbuild. We sell it in 10m lengths.