Linear Gap & Joint Fire SealingHead-of-Wall, Floor-to-Wall & Construction JointsLondon, Kent, Sussex & Surrey
Seal head-of-wall, deflection head, floor-to-wall and construction joints to certified detail — using tested backer and sealant systems by joint width and movement — so the compartment line is continuous at every junction, evidenced and recorded.
5 years' passive fire experience. Every joint sealed to a tested detail and recorded.
What this service is — and when you need it.
Installation of certified backer and sealant systems into linear gaps and construction joints — head-of-wall, floor-to-wall, wall-to-wall and slab junctions — sized to joint width, movement and required fire rating.
HRB duty holders, housing associations, principal contractors, healthcare estates, fit-out contractors and duty holders closing out FRA compartmentation actions on linear defects.
During refurbishment, on new-build handover, after FRA surveys flag open head-of-wall or junction defects, and when compartment walls have been altered or extended.
Linear gaps are the most commonly missed compartmentation defect. A perfect compartment wall with an unsealed strip above the head is not a compartment wall at all. Sealing to a tested detail closes the line at the junction where it most often fails.
The consequence of leaving it.
- An unsealed head-of-wall lets fire and smoke pass directly into the ceiling void — the fastest route between compartments.
- Movement joints that crack the sealant on first thermal cycle behave as if unsealed.
- Linear gap failures are one of the top findings on FRA compartmentation surveys — leaving them open drives repeat remedials.
What we see go wrong.
- Filling a head-of-wall joint with generic silicone or acoustic sealant — not a fire sealing system.
- Ignoring joint movement — a rigid seal on a deflection head detail cracks off in the first year.
- Skipping the backer rod, or using the wrong depth — the sealant doesn't achieve its tested performance.
- No dimensional record — the assessor can't verify the sealed joint width matches the certified system.
A step-by-step system, from survey to handover.
-
Step 1Joint survey
Every joint on the scope measured for width, depth and movement class, and logged against a floor plan.
-
Step 2System selection
Certified backer and sealant system paired to joint width, movement class, substrate and required fire rating.
-
Step 3Preparation and installation
Joint prepared and cleaned, backer rod set to the certified depth, sealant tooled to the certified profile.
-
Step 4Dimensional and photo record
Joint width and sealed depth recorded, and completed joint photographed against the location reference.
-
Step 5Handover pack
Record of Insulation, product datasheets and location-referenced photo and dimension pack handed over for the safety file.
Specific outcomes, not vague promises.
The compartment wall meets the slab — sealed to a tested detail — instead of stopping short.
Deflection head details use sealants and geometry rated for the joint's movement, so the seal doesn't crack off.
Each joint photographed and dimensioned against a location, ready for FRA re-inspection.
Correct system first time means the joint doesn't reappear on next year's remedial list.
Sealed alongside compartmentation and stopping, not stitched together across separate visits.
Record of Insulation and datasheet pack that survives assessor and insurer scrutiny.
Materials, methods and where each applies.
The technical detail behind how linear gap & joint fire sealing is scoped, specified and installed to certified detail.
Head-of-wall and deflection head joints
The join between the top of a compartment wall and the slab above is often incomplete. Where the wall is designed to accommodate slab deflection, the joint needs a system rated for that movement class — otherwise the sealant cracks on first thermal cycle. System selection depends on joint width, movement and substrate on both sides.
Floor-to-wall and wall-to-wall junctions
Joints between different construction elements — a partition meeting a party wall, a concrete slab meeting a stud wall — each need a certified detail specific to the substrate combination and joint width.
Construction joints in concrete and blockwork
Movement and construction joints running through slabs and walls need sealing that respects the joint's structural function while restoring the fire rating. Mortar-plus-sealant and specialised joint sealing systems are selected against the certified schedule.
Sealant types and backer rod selection
Not every fire sealant is rated for every joint width. Sealant depth to width ratio, backer rod type (open- vs closed-cell) and priming requirements all come from the tested system datasheet.
Coordination with compartmentation and stopping
Linear gap work is almost always adjacent to compartment wall repair and service penetration sealing. Delivering all three from one team removes the joins where responsibility usually splits.
What we do not offer
We do not offer a product warranty on the sealed joint. The certified sealant system's own third-party test evidence is the assurance; our commitment is to install to the tested schedule and provide evidence.
Straight answers on cost, timing and process.
How much does linear gap sealing cost?+
Priced by linear metre and joint type. Send a scope or an FRA extract with joint locations and you'll get a fixed quotation.
How long does the work take?+
Head-of-wall runs on a residential floor are typically days per floor; small commercial scopes complete in a single visit.
Do you provide a warranty on the sealed joints?+
No product warranty is offered. The certified sealant system's own test evidence is the assurance; our deliverable is evidenced installation to the tested detail.
How long does a sealed joint last?+
Correctly installed to the movement class of the joint, the seal performs for the life of the construction. Failures usually trace back to the wrong sealant for the joint movement, or an incorrect backer.
Can you work in occupied buildings?+
Yes — access is phased and dust is controlled.
Do you seal around metal deck and profiled slab details?+
Yes — profiled slab head-of-wall details have their own tested systems and we specify accordingly.
Can this be combined with other passive fire scope?+
Yes — linear gap sealing is usually delivered alongside penetration stopping and compartmentation repair as one coordinated package.
Which areas do you cover?+
London, Kent, Sussex, Surrey and surrounding boroughs including Croydon, Sutton, Bromley, Sevenoaks and Crawley.
Do you handle FRA close-out on linear gap actions?+
Yes — evidence per joint, referenced back to the FRA action number.
Get a fixed quotation for linear gap & joint fire sealing.
Send the FRA action list, drawings or a short scope description. You'll speak to Michael directly — not a call centre — and get a scoped, priced programme back.
Ready to scope your linear gap & joint fire sealing works?
Send the FRA or a short brief. You'll get a priced, evidenced programme back — not a template quotation.