Sika Sikaflex-400 Fire
A single-component, elastic polyurethane sealant that keeps fire-rated movement and connection joints both watertight and fire-resistant for up to four hours.
What is it?
A one-component, moisture-curing polyurethane joint sealant that has been fire-tested to EN 1366-4 and AS 1530.4, so a single bead handles both joint movement and fire compartmentation.
Where is it used?
Fire-rated movement and connection joints in walls, floors and facades of commercial buildings, car parks, basements and around fire-door perimeters.
Why use it?
It combines up to 4 hours of fire resistance with plus/minus 25 percent movement accommodation, removing the need for a separate fire barrier and a separate movement sealant in the same joint.
How is it applied?
Gun-applied from a 600 ml foil pack into a primed, correctly dimensioned joint over a backing rod, then tooled to a firm concave finish.
About Sika Sikaflex-400 Fire
Sikaflex-400 Fire is Sika’s fire-rated member of the Sikaflex polyurethane family, built for the joints that most sealants are not allowed to touch: the ones that have to move with the structure and hold a fire rating at the same time. It is a single-component, moisture-curing polyurethane that cures on contact with atmospheric humidity to a tough yet elastic rubber. What sets it apart from a standard facade or movement sealant is that its performance in a fire has been characterised in accredited tests to EN 1366-4 and AS 1530.4, so a specifier can point to a tested system rather than a marketing claim. In everyday service it behaves like any good PU sealant, staying flexible from minus 40 to plus 70 degrees Celsius; in a fire it resists the passage of flame and hot gases for a period that, depending on joint geometry and the tested build-up, can reach four hours.
For contractors working in India, the appeal is practical. Fire-stopping a moving joint traditionally meant layering a fire barrier or intumescent product and then sealing over it, which is slow, easy to get wrong on site, and hard to inspect. Sikaflex-400 Fire lets the same joint do both jobs with one gun-applied bead, which speeds up the programme and gives the fire consultant a cleaner detail to sign off. It bonds to concrete, masonry, metal and many other common substrates, is grey to blend with concrete and stonework, and tools easily to a neat finish. Because it is a Sika-tested product, it slots directly into the manufacturer’s fire-rated joint systems, which is what a building control authority or third-party certifier will ultimately want to see.
The technical insight
The product works on two levels that most people never see combined in one material. Chemically it is a moisture-curing polyurethane: the wet paste reacts with atmospheric humidity and skins over in roughly two hours, then cures inward at about 2.5 mm per 24 hours at 23 degrees Celsius and 50 percent RH, finishing as a low-modulus elastomer with around 85 percent elastic recovery. That elasticity is what lets it stretch and compress with a joint through plus/minus 25 percent of its width (rated to ISO 9047; the wider plus/minus 35 percent figure quoted elsewhere is to ASTM C719) without tearing or debonding. The fire performance comes from how the cured polyurethane behaves under intense heat: instead of melting and opening the gap, it chars and holds position long enough to block flame and hot gases. Crucially the rating is a property of the whole tested assembly, not the sealant alone, joint width, depth, backing material and substrate are all part of the certified build-up. That is why matching the site joint to a specific tested configuration in the TDS is not box-ticking; it is the only way the four-hour claim actually holds on your project.”
Where it is used
- Fire-rated movement joints in reinforced-concrete commercial and institutional buildings
- Linear connection joints between fire-compartment walls and floors
- Perimeter sealing around fire-rated doors, frames and shutter assemblies
- Head-of-wall and wall-to-floor joints in fire-separating partitions
- Expansion and movement joints in car parks, basements and podium slabs
- Sealing of service penetrations on both porous and non-porous substrates
- Facade movement joints where a fire rating is also specified
- General elastic movement joints in concrete, masonry and metalwork
Key advantages
- Delivers fire resistance and joint movement in a single gun-applied bead, removing a separate fire barrier
- Fire performance tested to EN 1366-4 and AS 1530.4, giving certifiers a documented system to approve
- Up to 4 hours fire resistance depending on the tested joint configuration
- Accommodates plus/minus 25 percent joint movement (ISO 9047) with roughly 85 percent elastic recovery
- Bonds to concrete, masonry, metal and most common construction substrates
- Single-component and moisture-curing, so there is no mixing and no pot-life pressure on site
- Tools easily to a clean concave finish and stays serviceable from minus 40 to plus 70 degrees Celsius
- Grey colour blends naturally with concrete and stonework
Limitations & considerations
- The four-hour rating only holds if the site joint matches a specific tested configuration in the TDS, not for arbitrary joint sizes
- Effective joint width band is limited (roughly 10 to 25 mm); very wide joints need a different detail
- Being polyurethane, prolonged UV exposure can chalk or discolour the surface over years, so it is not a decorative facade sealant
- Requires primer on many porous substrates and disciplined backing-rod and depth control to perform
- Not a substitute for tested penetration seals or ablative products where those specific systems are specified
- Application is restricted to substrate and ambient temperatures of plus 5 to plus 40 degrees Celsius, with the substrate kept above the dew point
Selection & best practice
Treat the joint detail, not the tube, as the product. Before sealing, confirm the actual joint width and depth against a tested configuration in the current Sika TDS and set the depth with a closed-cell backing rod so the sealant bonds only to the two joint faces, never the base (two-sided adhesion is what lets it stretch). Clean substrates back to sound, dust-free material and prime porous surfaces such as concrete as directed. Apply only when substrate and air are between plus 5 and plus 40 degrees Celsius and the substrate is at least 3 degrees above the dew point, then gun the bead in fully and tool it firmly to a concave profile so it wets both faces without voids. Protect fresh sealant from water until it has skinned (around two hours), and remember the full cross-section cures slowly at roughly 2.5 mm per day, so deep joints take time to reach full properties. Keep the batch documentation and the tested-system reference on file for the fire consultant.
Specifications
| Chemical base | Single-component, moisture-curing polyurethane |
| Colour | Grey |
| Density | Approx. 1.40 kg/l |
| Movement capability | Plus/minus 25% (ISO 9047); plus/minus 35% (ASTM C719) |
| Fire resistance | Up to 4 hours, tested to EN 1366-4 and AS 1530.4 |
| Skin / tack-free time | Approx. 120 minutes at +23°C / 50% RH |
| Curing rate | Approx. 2.5 mm in 24 h at +23°C / 50% RH |
| Elastic recovery | Approx. 85% |
| Service temperature | -40°C to +70°C |
| Application temperature | +5°C to +40°C (substrate min. 3°C above dew point) |
| Packaging | 600 ml foil pack (unipack), 20 per box |
Industry use cases
Commercial & IT Buildings
Fire-rated movement joints between floor slabs and compartment walls where fire consultants demand a tested, movement-capable seal rather than a rigid mortar fill.
Car Parks & Basements
Expansion and connection joints in multi-level parking structures that must move with thermal cycling yet maintain fire separation between decks.
Hospitals & Institutional
Perimeter and head-of-wall joints around fire-rated doors and partitions in high-occupancy buildings where compartmentation is life-safety critical.
Industrial & Warehousing
Wall-to-floor and service-penetration joints in fire-separating walls that also see structural and thermal movement.
High-Rise Residential
Connection joints in precast and cast-in-situ fire-compartment construction where a single detail must satisfy both movement and fire-stopping requirements.
Frequently asked questions
Is Sikaflex-400 Fire really rated for four hours of fire resistance?
How is it different from a standard Sikaflex movement sealant?
How much joint movement can it take?
Do I need a primer and a backing rod?
What pack size does it come in and what colour?
Can I use it as a penetration seal for cables and pipes?
How we position Sika Sikaflex-400 Fire
Sikaflex-400 Fire is the specialist to reach for only when a joint must move and hold a fire rating; for ordinary weathersealing and movement joints without a fire requirement, the standard Sikaflex PU range or a modified-silane product like Sika’s own MS-based sealants are more cost-effective. On the same project, pair it with Sika’s fire-rated penetration and firestop systems where cables and pipes cross compartment lines, and use a general facade sealant for non-rated external joints. Where the client is standardised on Fosroc, our Fosroc Nitoseal PU40 covers the non-fire-rated PU movement joints on the same site, though it is not a substitute wherever a fire rating is specified.
Fosroc Nitoseal PU40 — Choose Nitoseal PU40 only for standard, non-fire-rated polyurethane movement joints on the same project; it matches Sikaflex-400 Fire on movement and substrates but carries no fire rating, so it cannot replace it wherever fire resistance is specified.
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