Install Backer Rod

What happens here

When dealing with deeper or wider gaps, such as those found around older interior window frames or where trim meets an uneven wall, a backer rod should be inserted. The video shows this process with a gray, flexible foam rod being pushed into a large vertical gap using a putty knife. In an interior setting, backer rods ensure the caulk bead has the correct depth-to-width ratio (typically 1:2 to 1:1, but never exceeding 1/2 inch deep regardless of width) for optimal flexibility and durability. This prevents the caulk from adhering to the back of the joint (3-sided adhesion), which can lead to premature cracking when the joint moves. It also reduces the amount of caulk needed.

Goal: For deeper or wider gaps (typically exceeding 1/4 inch) around interior windows or trim, insert a backer rod to optimize caulk performance and minimize product usage.