Fireproof putty sealing techniques for cable trays

Fireproof putty is recommended for sealing cable trays to prevent fire and smoke spread, providing up to 4 hours of fire protection when properly applied.

Purpose and Benefits

Fireproof putty, such as 3M™ Fire Barrier Moldable Putty Stix MP+ or Hilti CP 619 T, is designed to seal openings around cable trays, conduits, and cables passing through fire-rated walls or slabs. It helps contain fire and smoke at the source, reduces heat penetration, and maintains the integrity of fire-rated assemblies . The putty is pliable, conformable, and adheres well to most construction substrates, including metal and plastic, making it suitable for various cable tray configurations .

Application Guidelines

• Opening Preparation: Ensure the floor or wall finishes are complete and the shaft doors are installed. Large openings may require a fire-resistant backing plate before applying putty .
• Sealing: Mold the putty directly onto the substrate or around cables and trays. The material should fill all gaps tightly, leaving no visible cracks or voids .
• Thickness and Coverage: Follow manufacturer specifications for minimum thickness and coverage. For example, 3M putty sticks provide up to 4 hours of fire protection and are re-enterable for future cable additions .
• Compatibility: Fireproof putty is compatible with synthetic cable jackets, steel or plastic electrical boxes, and can be used in both new construction and retrofits .

Fire Ratings and Standards

• 3M Moldable Putty Stix MP+ are tested up to 4 hours in accordance with ASTM E 814 (UL 1479) and up to 2 hours per ASTM E 119 (UL 263) when installed according to UL wall-opening listings .
• Hilti CP 619 T and similar products are UL-listed and designed to prevent fire and smoke spread through large openings .

Practical Tips

• Use enough putty to completely fill the gap around the cable tray; for example, 3M recommends two sticks per opening for standard installations .
• Ensure orderly placement of firestop packs or putty to maintain consistent coverage and allow for maintenance or future cable additions .
• Verify that the putty adheres well and remains pliable over time, as aging properties are important for long-term fire protection . Using fireproof putty correctly ensures that cable tray penetrations meet fire safety codes, maintain structural integrity, and provide reliable protection against fire and smoke spread.