Every pipe, cable or duct that passes through a fire-resisting wall or floor leaves a gap. So do the joints around many fire door frames. If those gaps are left open, or filled with the wrong material, fire and smoke can pass through. Fire-rated sealants are one of the ways these gaps are closed. This guide explains what they are, why the tested detail matters and what to ask before work starts.
Intumescent and fire-rated: what the words mean
Intumescent sealant expands when it is heated. In a fire, it swells to fill the gap and help stop flames and hot gases getting through. It is often used around service penetrations and in linear gaps.
Fire-rated sealant is a wider term. It covers any sealant that has been tested to show it can keep its performance in a fire for a set time, in a set joint. Some are intumescent, some are not.
Neither is the same as ordinary silicone or decorators’ caulk, which are not designed to hold back fire.
Why the tested detail matters
A fire-rated sealant is tested in a particular arrangement: a certain gap width and depth, a certain backing material, certain surfaces either side and a certain orientation. Its fire rating only applies when it is installed the same way.
So the right product in the wrong joint may not give the rating on the cartridge. A gap that is too wide, a joint that is too shallow, or a missing backing material can all mean the seal won’t perform as expected. Manufacturers publish the tested details, and installers should follow them.
Who decides what is needed
The sealant installer is not the person who decides where fire-rated sealant is needed or what rating it must achieve. That comes from the building’s designer, the fire strategy or the fire risk assessment.
In England and Wales, the responsible person for most non-domestic premises must carry out and regularly review a fire risk assessment (GOV.UK: fire risk assessments). Scotland has its own fire safety law and guidance (gov.scot practical fire safety guidance).
Need it done properly? Mr Mastic covers the South East, London and Scotland, with a one-year guarantee on every job. Call or email for a quick quote.
What we do, and what we don’t
Our fire-rated sealant service installs intumescent and fire-rated sealant around service penetrations, door frames and linear gaps. We work to the specification given by the fire risk assessor or designer, and to the manufacturer’s tested details.
We don’t carry out fire risk assessments, and we don’t certify buildings. If you don’t yet know what your building needs, speak to a competent fire risk assessor first. Then we can install to their specification.
What to ask your installer
- Which product will you use, and which tested detail does this joint match?
- What gap widths and depths does that detail allow?
- Is a backing material needed, and which one?
- How will each sealed gap be recorded, for example with photos or labels, if your specification asks for it?
- What will you do if a gap falls outside the tested range?
Good answers are specific. Our checklist for choosing a mastic man has more questions for commercial sites.
Keeping fire seals intact
Fire-rated seals are often damaged long after they are installed. A new cable is pushed through a sealed gap, a pipe is rerouted or a section is cut out for access and never made good. Each of these can leave an opening in a fire-resisting wall or floor.
It helps to make checking these seals part of routine inspections, and to make sure anyone working in ceiling voids or service risers knows to report or make good any seal they disturb.
Quick answers
Can I use ordinary silicone around a fire door?
Not where the specification calls for a fire-rated seal. Ordinary silicone isn’t designed or tested to resist fire.
Does intumescent sealant need replacing?
It can be damaged by later works, such as new cables pushed through a sealed gap. Damaged seals should be made good to the original specification.
Do you issue fire certificates?
No. We install to the specification and the manufacturer’s tested details. We don’t certify buildings or carry out fire risk assessments.
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- All advice
This guide is general information about sealant work. It isn’t legal, fire-safety or structural advice; for those, speak to a qualified professional.