How to seal fireproof putty inside cable trays

To seal fireproof putty on cable trays, ensure all gaps around the tray are tightly filled with UL-listed firestop putty or caulk, use backing plates for large openings, and maintain continuous coverage without cracks or voids.Step-by-Step Guidance

1. Prepare the Opening Before applying putty, ensure the wall or floor penetration is clean and free of debris. For large openings, install a fire-resistant backing plate to support the putty and maintain structural integrity during a fire event . 2. Select Appropriate Firestop Materials Use UL-listed firestop putty sticks (e.g., 3M FSP-MPS) or firestop caulk suitable for cable tray penetrations. These materials are pliable, conformable, and adhere well to metal and non-metal surfaces . For multi-cable or large tray penetrations, consider modular firestop systems like FIRSTO or SLIPSIL for enhanced sealing . 3. Apply the Putty

• Mold the putty around the cable tray, filling all gaps between the tray and the wall or floor.
• Ensure the putty completely surrounds the tray and penetrates any voids.
• For trays passing through walls, extend the putty about 12 inches on each side of the penetration if using covers, allowing drywall or finishing work to be completed without compromising the seal . 4. Install Fire Partitions or Barriers For long cable trays, install fire partitions every 20 meters to limit fire spread along the tray . This can be done using fire-rated boards or intumescent barriers. 5. Inspect and Finish
• Check for visible cracks or voids; the seal must be continuous and reliable.
• Cover plates should be square, evenly painted, and properly aligned to protect the putty and maintain fire integrity .
• For retrofits, split sleeves or modular inserts can be used to add putty around existing cables without removing them . 6. Optional Coatings Spraying fire-retardant paint on cable bundles near exits or high-risk areas can provide additional protection, complementing the putty seal .

Key Considerations

• Maintain UL or local code compliance by using approved firestop materials.
• Ensure packing thickness and gap coverage meet fire-rating requirements (e.g., 20–30 mm for slab penetrations).
• Reuse or adjust modular systems if cable configurations change, ensuring ongoing fire protection . By following these steps, you can effectively seal cable tray penetrations with fireproof putty, preventing fire and smoke spread while maintaining compliance with fire safety standards.