Thermwell F4 Mortite Caulking Cord 45 Ft Gray

Product Description

The THERMWELL F4 is a gray, rope-style caulking cord designed for sealing gaps and air leaks around windows, doors, and other building envelope penetrations. Sold in a 9.5-ounce roll spanning 45 feet, this Mortite-formulated weatherstrip compound presses into place by hand without tools, conforming to irregular surfaces and creating an effective barrier against drafts and moisture infiltration. It is commonly installed by HVAC technicians, general contractors, and building maintenance professionals as a seasonal or semi-permanent air-sealing solution on both residential and light commercial structures.

The F4 caulking cord is suited for interior and exterior applications where a non-hardening, repositionable seal is needed. Typical use cases include sealing window sash channels, door frames, basement rim joists, and utility penetrations in wall assemblies. Because it remains pliable after application, it can be removed at the end of a heating season without damaging surrounding surfaces, making it a preferred choice for seasonal weatherization programs.

Key Features

• 45-foot roll provides ample length for multiple window and door sealing applications per roll
• 9.5-ounce Mortite formula stays pliable and non-hardening after application
• Gray color blends with common window frame, concrete, and masonry finishes
• Hand-applied without caulk gun or specialized tools
• Repositionable and removable without surface damage
• Effective barrier against air infiltration and moisture intrusion

Compatibility

Designed as an OEM-style weatherization product suitable for use on residential and light commercial window frames, door frames, and general building envelope gaps where a hand-applied, non-hardening caulking cord is appropriate.

Installation Notes

Installation does not require power shutoff, but surfaces should be clean, dry, and free of loose paint or debris before application for best adhesion. Press the cord firmly into the gap or channel by hand, overlapping at corners. No caulk gun is required. For exterior applications, follow local building energy codes for acceptable air-sealing methods.