Correct Method for Sealing Cable Trays with Fireproof Putty

Use approved firestop putty, ensure tight and complete sealing around cables, and follow layering and inspection best practices to maintain fire-rated integrity.

Material Selection

Choose fire-rated putty or caulk specifically designed for electrical penetrations, such as 3M Fire Barrier Moldable Putty+ or intumescent caulks. These materials expand under heat to seal gaps and prevent fire and smoke spread. For larger openings, consider using fire-resistant backing plates or wrap strips to support the putty and ensure complete coverage.

Preparation

Measure openings accurately: Reserve openings slightly larger than the cable tray dimensions (typically 100–200 mm extra) to allow proper sealing. Clean surfaces: Remove dust, debris, and moisture from the tray edges and wall or floor penetration to ensure good adhesion. Install backing plates if needed: For large gaps, a fire-resistant plate provides a stable surface for putty application.

Application Techniques

Layering: Apply putty in layers, pressing it firmly around each cable and tray edge to eliminate voids. Gap filling: Ensure all gaps between cables, trays, and the penetration are completely filled. The gap area should not exceed 1 cm², and packing thickness should meet manufacturer specifications.

Use of collars or wrap strips: For snug penetrations, a one-piece metal collar combining moldable putty and intumescent wrap strip can be used to secure the seal. Smooth finish: Level the putty surface to create a uniform, visually appealing finish while maintaining firestopping effectiveness.

Inspection and Maintenance

Check for cracks or voids: After curing, inspect the seal to ensure there are no gaps that could compromise fire protection. Periodic review: For outdoor or high-humidity environments, inspect trays and seals regularly for corrosion, moisture, or damage. Reusability: Some putty systems allow for retrofitting or adding additional cables without compromising the firestop.

Additional Considerations

Segregate power and signal cables to reduce interference and simplify firestopping. Maintain clearance between cables to prevent heat accumulation and ensure proper airflow. Minimize opening size to reduce material usage and labor costs while maintaining compliance.

By following these tips, you can achieve a reliable, code-compliant firestop for cable trays that protects both the building structure and occupants in the event of a fire.