How many metres does a cartridge of fire mastic cover?

Coverage depends on the joint width and depth. A standard 310ml cartridge of intumescent sealant covers approximately 3.1 metres of a 10mm x 10mm joint, 1.5 metres of a 10mm x 20mm joint, or 1.0 metres of a 10mm x 30mm joint. Larger joints use significantly more sealant. Always allow 10-15% extra for waste, cut-off and tooling. The calculator provides exact coverage based on your joint dimensions.

What is the difference between fire-rated and standard sealant?

Fire-rated sealant (intumescent mastic) contains materials that expand when exposed to fire, sealing gaps and preventing fire and smoke spread. Standard silicone or acrylic sealant will burn, melt or fall away in a fire, providing no fire resistance. Fire-rated sealants are tested to BS EN 1366-3 (penetration seals) or BS EN 1366-4 (linear joints) and carry specific fire ratings (30, 60, 120 minutes). Only fire-rated products should be used in fire-resisting construction.

When is fire mastic required vs fire cement?

Fire mastic (intumescent sealant) is preferred for joints that may experience movement, around service penetrations where flexibility is needed, and for finishing exposed seal faces. Fire cement is better for rigid applications in masonry and concrete walls, large void filling and where a hard finish is required. Fire cement typically costs less but cannot accommodate movement. For door frames, intumescent sealant is standard. For pipe penetrations through concrete, either product works.

What depth of fire sealant is required?

The required depth depends on the fire rating and the specific product. Typical minimum depths are: 10-15mm for 30-minute rating, 15-25mm for 60-minute rating, and 25-50mm for 120-minute rating. The depth must always match the manufacturer tested detail — installing less than the tested depth invalidates the fire rating. For gaps wider than 10-15mm, a mineral wool backing rod or fire batt must be installed first to support the sealant.

Does fire mastic need to be inspected?

Yes, all fire stopping including fire mastic seals must be inspected before being concealed. Under the Regulatory Reform (Fire Safety) Order 2005, photographic records of fire stopping installations must be kept. Building control may request to inspect fire stopping during construction. Fire mastic seals should also be checked during fire risk assessments — deteriorated, cracked or missing sealant must be replaced to maintain the fire resistance of the construction.

TradeCalculator

Fire Mastic Calculator

Calculate fire-rated sealant and mastic quantities for penetration seals, linear joints and door frame seals per BS EN 1366.

Application Type

Type of fire seal being applied

Sealant Type

Fire-rated sealant product type

Fire Rating

Required fire resistance period

Number of Penetrations / Doors

Total seals to make

Penetration Diameter / Width

Pipe diameter or opening width

Joint / Gap Width

Width of the gap to seal

How We Calculate This

This calculator determines the volume of fire-rated sealant needed and the number of cartridges required, based on joint dimensions and the number of seals.

How it works

Penetrations: Calculates annular gap volume around pipes/cables.
Linear joints: Width x depth x length for continuous joint seals.
Waste factor: Adds allowance for cut-off, tooling and over-application.
Cartridge count: Total volume divided by cartridge size (typically 310ml).

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.