Closed-Cell Backer Rod Foam Caulk Saver for Slab & Penetration Sealing

The backer mitigators use under RadonAway Pro Sealant

Closed-cell polyester foam backer rod for sealing the gaps that radon mitigation actually encounters: 4" PVC pipe through an oversized cored hole, foundation hairline cracks, sump-pit perimeters, and sub-slab depressurization air-leak points. Compresses to fill the gap, doesn't absorb water, and gives the polyurethane sealant a controlled depth to bond against.

Why closed-cell vs. open-cell

• Closed-cell doesn't absorb water — critical for damp basements and sub-slab work where moisture is present
• Closed-cell doesn't compress under sealant cure — so the sealant joint actually achieves the joint depth specified by ANSI/AARST
• Open-cell rod (often sold as cheaper substitute) swells in moisture and fails airtight seal over time — not what you want behind a mitigation system

Specifications (all sizes)

• Length: 59 ft (18 m) per roll
• Material: Closed-cell polyester foam, grey
• Waterproof: Yes — non-absorbent, won't wick moisture
• Maximum gap fill: 1.5" (depending on rod size and joint depth)
• Flexible: Bends and twists to follow irregular gap geometry

Choosing your size

• 3/8": Tight hairline cracks, narrow expansion joints, slab-edge gaps
• 1/2": Standard slab crack work, most pipe-to-concrete penetrations under SlabCollar
• 5/8": Medium gaps around oversized cored holes for 4" Sch 40 PVC
• 3/4": Large gaps, sump-pit perimeters, foundation-to-floor expansion joints

Installation

1. Pre-clean the gap of dust and debris
2. Press backer rod into the gap to the recommended depth (typically half the gap width below the surface)
3. Apply RadonAway Pro Sealant over the backer rod, tooling to a smooth surface
4. Allow polyurethane sealant cure time per manufacturer instructions before activating fan

For penetration sealing where a flanged EPDM gasket is appropriate, see SlabCollar 4" EPDM Seal instead of backer rod + sealant.