Fosroc Nitoseal MB333 (formerly Nitoseal 333)
Hot-poured, high-extension polymer-modified bitumen sealant to BS 2499 Type N1 for movement joints in concrete roads and asphalt pavements.
What is it?
A hot-applied, polymer-modified bitumen joint sealant (formerly branded Nitoseal 333) that pours molten into pavement joints and sets to a tough, resilient rubber-like seal complying with BS 2499:1993 Type N1.
Where is it used?
Butt and expansion joints in concrete carriageways, service roads, hardstandings, bridge approaches and asphalt surfacing where vehicles run directly over the sealed joint.
Why use it?
It keeps water, grit and debris out of the joint while flexing with daily and seasonal movement, protecting the joint arris and sub-base and extending pavement life.
How is it applied?
The block or pellet compound is melted in a thermostatically controlled boiler to 165-175C and poured into a primed, dry joint; it returns to traffic quickly once cooled.
About Fosroc Nitoseal MB333 (formerly Nitoseal 333)
Nitoseal MB333 is the current name for the product long known in the field as Fosroc Nitoseal 333, and it remains one of the most familiar hot-poured joint sealants on Indian road and pavement projects. It is a polymer-modified bitumen compound supplied as a solid that is melted on site and poured molten into the joint. On cooling it forms a flexible, self-levelling seal that bonds to both concrete and asphalt and accommodates the repeated opening and closing that every trafficked joint experiences. The formulation meets BS 2499:1993 Type N1, the classification for normal-performance hot-applied sealants used in surfaces carrying vehicles.
For engineers and contractors, the appeal is a straightforward, proven system rather than a specialist high-tech product. Once the boiler is at temperature and the joint is clean, dry and primed, sealing is fast and the pavement can usually be reopened to traffic within a short window. The cured seal resists the ingress of water and incompressible grit that would otherwise work into the joint and spall the concrete edges under wheel loads. Because it is a mature, widely stocked product, it suits routine road maintenance, new carriageway construction and hardstanding works where a dependable, economical joint seal is needed at scale.
The technical insight
The performance of a hot-poured sealant comes from what the polymer does to the base bitumen. Plain bitumen is cheap and sticky but behaves badly at the extremes: it flows and picks up under summer heat and traffic, and it goes brittle and cracks in the cold. Nitoseal MB333 is modified with polymers that raise the softening point and add elastic recovery, so the cured seal behaves more like a rubber than a tar. That elasticity is what lets it absorb roughly 25% movement across a butt joint without splitting from the joint face or tearing internally. The material is designed to be poured hot into the joint so it wets out the primed concrete or asphalt walls completely and grips the full depth of the sealing slot as it cools, rather than sitting as a skin on top. Getting the pour temperature right matters: too cool and it will not flow into the joint or bond properly; overheated and repeatedly re-boiled, the polymer network degrades and the sealant loses its extension. Correct joint geometry, a sound primer coat and a controlled melt are therefore the three levers that decide whether the seal lasts years or fails in a season.
Where it is used
- Sealing transverse and longitudinal joints in concrete road carriageways
- Expansion and contraction joints in industrial hardstandings and container yards
- Joints in concrete aprons, service roads and parking areas
- Sealing joints in asphalt (bituminous) surfacing and overlays
- Bridge deck approach and pavement joints subject to traffic
- Routine maintenance and resealing of failed or aged pavement joints
- Joints in warehouse and factory external pavements
- Airport taxiway and hardstanding pavement joints where an N1 sealant is specified
Key advantages
- Complies with BS 2499:1993 Type N1 for hot-applied trafficked-joint sealants
- Accommodates around 25% movement in butt joints without loss of seal
- Polymer modification gives elastic recovery and a raised softening point versus plain bitumen
- Bonds well to both concrete and asphalt substrates
- Fast return to traffic once the poured seal has cooled
- Resists ingress of water, dirt and incompressible grit that spalls joint edges
- Well proven and widely available across India for road and pavement works
- Economical, straightforward system for large-volume jointing
Limitations & considerations
- Requires hot melting in a thermostatically controlled boiler; not a ready-to-use cartridge
- Overheating or repeated re-boiling degrades the polymer and reduces extension
- Movement capacity (about 25%) is lower than premium cold-applied polyurethane or silicone sealants
- Not intended for fuel- or jet-blast-exposed pavements, where a fuel-resistant sealant is required
- Joint must be dry, clean and correctly primed with Fosroc Primer B2 or bond and durability suffer
- Application in wet conditions or onto damp joints is not permitted
Selection & best practice
Design the sealing slot to suit the expected movement, following BS 6093 guidance, and keep within the normal maximum of about 30 mm width and 25 mm depth. Saw or rout the joint to clean, sound faces, then remove all dust, laitance, oil and old sealant; the joint must be completely dry before priming. Apply Fosroc Primer B2 to both joint faces and allow the correct tack-off time. Melt the compound in a thermostatically controlled, indirectly heated boiler and pour within the recommended range of 165-175C, never exceeding the maximum melt temperature and avoiding prolonged holding or repeated re-boiling. Use a bond breaker or backing rod where required so the sealant adheres to two faces only and can flex freely. Pour to slightly overfill, allow to cool and cure, and reopen to traffic only once the seal has firmed. On hot days schedule work for cooler hours to control the pour and set.
Specifications
| Product type | Hot-poured, high-extension polymer-modified bitumen joint sealant |
| Former name | Nitoseal 333 (now Nitoseal MB333) |
| Standard | BS 2499:1993 Type N1 |
| Movement accommodation | Approximately 25% in butt joints |
| Pouring / application temperature | 165-175C (thermostatically controlled boiler) |
| Maximum joint width | 30 mm |
| Maximum joint depth | 25 mm |
| Recommended primer | Fosroc Primer B2 |
| Pack size | 15 kg |
Industry use cases
Highways & Roads
Sealing transverse and longitudinal joints in new concrete carriageways and resealing aged joints during periodic maintenance, keeping water and grit out of the slab edges.
Industrial Pavements
Movement joints in factory hardstandings, container yards and heavy-duty external pavements that must take repeated wheel and axle loads.
Logistics & Warehousing
Joints in warehouse aprons, loading yards and service roads where a durable, quickly trafficable seal reduces downtime.
Bridges & Approaches
Pavement and approach-slab joints on bridge decks where a flexible, N1-compliant hot-poured seal is specified for trafficked surfaces.
Airport & Aviation Pavements
Taxiway, apron and hardstanding joints where a BS 2499 Type N1 sealant is called for in non-fuel-exposed areas.
Frequently asked questions
Is Nitoseal MB333 the same as the old Nitoseal 333?
Is this a silicone or a cartridge-gun sealant?
What is the correct pouring temperature?
How much movement can the joint take?
Does it need a primer?
Can I use it on a fuel-exposed or jet-blast pavement?
How we position Fosroc Nitoseal MB333 (formerly Nitoseal 333)
Nitoseal MB333 is Fosroc’s workhorse hot-poured sealant for standard trafficked pavement joints, and it usually specifies alongside Fosroc Primer B2, which prepares the joint faces for reliable adhesion. Where the pavement sees fuel spillage or jet blast, or where a cold-applied two-part system is preferred, Fosroc Colpor 200PF is the appropriate step up. For building, facade and glazing movement joints that this bitumen product does not serve, Fosroc’s Nitoseal silicone and polyurethane gun-grade sealants (such as the Nitoseal SC and PU ranges) are the correct choice. Space Arc supplies the full Fosroc joint-sealing range across Delhi NCR and Pan-India, and can advise on the matching primer, backing rod and boiler set-up, as well as equivalents from other brands we distribute where a project standard calls for them.
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