Thermwell C23H Caulk Saver Backer Rod 0.625 in X 20 Ft

Product Description

The THERMWELL C23H is a closed-cell poly foam backer rod designed to reduce caulk consumption when filling or sealing large gaps and openings. Measuring 0.625 inches in diameter and 20 feet in length, this caulk saver is pressed into a gap before caulking, limiting caulk penetration depth and creating a proper two-point adhesion profile. The resilient poly foam construction provides a moisture-repellent backing that holds its shape under compression. Plumbers, HVAC technicians, weatherization contractors, and general building trades installers use backer rod on expansion joints, window and door perimeters, foundation penetrations, and plumbing rough-in gaps before applying a topcoat of caulk or sealant.

The C23H is suited for residential and light commercial applications where gaps or joints require backing prior to caulking. Compatible with virtually every type of caulk and sealant, including silicone, latex, polyurethane, and butyl-based products, it provides a stable substrate that prevents caulk from sinking into deep or wide voids. Each package contains 10 units, providing 200 linear feet of backer rod total, making it practical for larger weatherization or renovation projects.

Key Features

• 0.625-inch diameter foam rod fills gaps before caulking to reduce sealant usage
• Resilient poly foam construction maintains shape and compression over time
• Moisture-repellent material resists water absorption
• Works with silicone, latex, polyurethane, butyl, and other caulk and sealant types
• 20 feet per roll, 10 units per package for 200 linear feet total

Compatibility

Compatible with virtually every type of caulk and sealant; suitable as a backer rod for gap-filling and joint-sealing applications in residential and light commercial construction.

Installation Notes

A licensed weatherization contractor, plumber, or general trades installer typically installs backer rod as part of air sealing or joint preparation work. Press the foam rod firmly into the gap to a depth that leaves adequate space for the caulk bead above it. Do not stretch or distort the rod during installation, as this can reduce its effective diameter and compromise the backing profile. Ensure the joint surface is clean and dry before applying caulk over the installed backer rod.