Using Fire-Boards for Large Service Penetrations (Pattress Seals)
- murtaza
- November 9, 2025
- Uncategorized
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A 2-hour fire-rated wall is useless if it has a large, unsealed hole in it. In KSA projects, these large openings are common, especially in service risers and plant rooms, where hundreds of cables, pipes, and ducts must pass through. Standard firestop sealant alone is not enough to seal an opening of this size. The solution is a “pattress seal,” also known as a “blank” or “slab seal,” which is built using high-density Fire-Boards.
A pattress seal is a robust, tested system that combines fire-rated boards with firestop sealants to fully restore the fire rating of a wall or floor that has a large or complex set of services passing through it.
In This Article:
When is a Pattress Seal Needed?
Standard firestop sealant is generally tested for annular gaps around single services. A pattress seal system is required when you have:
- Large Openings: Any hole in a wall or floor larger than about 300mm x 300mm.
- Complex, Mixed Services: A single opening containing a mix of cable trays, plastic pipes, copper pipes, and ducts.
- Cable Trays & Ladders: Sealing around high-density cable trays is best done with a board system.
- Future Capacity: A board system can be easily “re-entered” by a specialist to add new cables without destroying the entire seal.
How is a Fire-Board Seal Constructed?
This is a multi-step, specialist process that is a key part of our firestopping services.
- Board Selection: A high-density mineral wool or calcium silicate Fire-Board is selected.
- Board Installation: The board (or boards, in a double-layer system) is cut to the size of the opening and friction-fit or fixed into place.
- Service Penetration: The services (cables, pipes) pass *through* the fire-board.
- Sealing: This is the final, critical step. All gaps—between the board and the substrate, and between the services and the board—are sealed with a tested, intumescent firestop sealant.
Often, the entire face of the board is “ablation” coated with a fire-resistant coating to provide a final, monolithic seal.
Common Types of Fire-Board Seals
| Board Type | Common Name | Key Feature |
|---|---|---|
| High-Density Mineral Wool | “Batt” or “Slab” System | The most common type. Easy to cut and friction-fit. Must be used with an ablation coating. |
| Calcium Silicate | “Pattress” or “Rigid” System | Used for more heavy-duty applications, larger spans, or where a more robust, non-fibrous solution is needed. |
Integrating with Other Firestop Products
A pattress seal is a “matrix” that holds other firestop products. As seen in our past projects, a single board system may integrate:
- Intumescent Sealant: To seal all small gaps and air paths.
- Pipe Collars: Fixed *to the face* of the fire-board to protect plastic (combustible) pipes.
- Pipe Wraps: Used to wrap plastic pipes where they pass *through* the board.
This combination creates a single, tested, and compliant system for even the most complex penetrations.
“You can’t seal a 1-meter square hole with a tube of sealant. A fire-board pattress seal is the engineered, structural solution that makes large-scale firestopping possible.”
Conclusion: The Solution for Complex Openings
Fire-Board systems are a versatile and essential tool in the firestopper’s toolkit. They are the only SBC-compliant solution for sealing large, complex, and mixed-service penetrations. Their installation is a specialist trade, requiring a deep understanding of how fire-boards, sealants, and intumescent devices must work together to create a single, tested system.
Have large or complex service openings that need a compliant firestop solution?
