So, What’s the Difference Between N1 and N2 Sealant?

The difference between N1 and N2 sealant is the extension characteristics defined under BS EN 14188-1. N1 is an elastic, high-extension type hot applied sealant. It handles larger joint movement and is specified where joints experience significant thermal expansion and contraction. N2 is a normal, low-extension type hot applied sealant. It handles smaller joint movement and is specified where joint movement is more limited. Both are hot applied bituminous sealants, poured at similar temperatures, applied through the same equipment, and used on similar substrates. The choice between them is driven by expected joint movement, not by fuel resistance (fuel-resistant equivalents are classified separately under BS EN 14188-1 as F1 and F2).

At Shepherd and Sons, we apply both N1 and N2 grade hot applied sealants across UK highway and airfield work, with over 40 years of experience specifying and installing both. We’re based at Westerhill Farm in Kent, we’re members of the Extruded Sealant Association, and we work to the ESA Code of Practice and BS EN 14188-1. This article covers the technical difference between N1 and N2, when to specify each, the common misconceptions we correct in practice, and how the choice affects the joint’s long-term performance.

The BS EN 14188-1 classification explained

BS EN 14188-1 is the European standard governing hot applied joint sealants. It classifies them into four types by extension characteristics and fuel resistance:

• Type N1 – Elastic, high-extension (no fuel resistance requirement)
• Type N2 – Normal, low-extension (no fuel resistance requirement)
• Type F1 – Fuel-resistant, high-extension
• Type F2 – Fuel-resistant, low-extension

N1 and N2 are the two “normal” (non-fuel-resistant) grades. The difference between them is entirely about how much joint movement they can accommodate.

Elastic, high-extension (N1). Higher polymer modification. Handles larger joint movement without cracking, tearing or losing bond to the joint face. Recovers more of its shape after being stretched. Costs more per tonne because of the higher polymer content.

Normal, low-extension (N2). Less polymer modification. Handles smaller joint movement. Less capable of recovery after significant stretch cycles. More economical per tonne.

Both cure by cooling from a hot pour, both bond to concrete and asphalt, and both work with the same joint slot preparation, backer rod, and application discipline.

When to specify N1

N1 is the specification for joints subject to significant thermal cycling and structural movement. In UK practice, that typically means:

Concrete carriageway joints on motorways and A-roads. Concrete slabs expand and contract significantly between summer and winter. The joint movement range is wide, and a low-extension sealant will fatigue at the joint walls within a few seasons.

Airfield taxiway and apron joints. Large concrete pavement slabs on airfields see substantial thermal cycling, especially where sections are exposed to direct sun for long periods. N1 handles that movement across the service life.

Bridge deck joints. Structural movement from thermal expansion and traffic loading requires the higher extension capability of N1.

Longitudinal joints on wide pavements. Where cumulative slab-to-slab movement across a wide carriageway builds up, N1 is the standard specification.

Any joint where design engineering has calculated significant movement. If the design brief specifies a movement accommodation factor above the typical N2 range, N1 is the answer.

When to specify N2

N2 is the specification for joints subject to more limited movement. In practice:

Contraction joints in concrete slabs with modest thermal exposure. Where the joint spacing is close and the individual slab movement is small, N2 is sufficient.

Localised joint repairs on existing pavements. Where the original design used a normal-grade sealant and the movement pattern is proven to be within N2 capability, matching the specification makes practical and economic sense.

Sheltered or thermally stable environments. Indoor or covered concrete slabs where temperature swings are smaller than external pavements.

Cost-driven specifications on lightly trafficked pavements. Council car parks, low-volume service yards and similar sites where budget pressure and low movement combine to justify N2 rather than N1.

The common misconception, N2 is not fuel-resistant

This is the most frequent error we correct in specifications passed to us for review. N2 is not a fuel-resistant grade. The confusion arises because N2 is sometimes discussed alongside fuel-resistant applications in older technical literature, and because the alphanumeric similarity between N2 and F2 causes crossovers in casual reference.

Under BS EN 14188-1, if fuel resistance is required, the specification should be F1 (high-extension, fuel-resistant) or F2 (low-extension, fuel-resistant). Neither N1 nor N2 is tested against Test Fuel I or Test Fuel II as part of BS EN 14188-1 certification. Specifying N2 for a fuel-exposed joint on the assumption it delivers fuel resistance is a specification error we’ve had to correct on multiple projects.

For genuinely fuel-exposed joints, the practical UK specification is usually one of three routes:

1. Hot applied F1 or F2 fuel-resistant sealant for high-volume linear pavement work with fuel exposure
2. Cold applied two-part polysulfide (such as Thioflex 555, BS EN 14188-2 Class B, C or D) for aircraft fuelling aprons and specialist areas
3. One-part polyurethane (Sikaflex, Sea-Kar) for port and dockside environments

In our experience, N1 works better than N2 on concrete carriageway joints subject to full UK seasonal thermal cycling because the higher extension capability accommodates the movement range without fatigue cracking at the joint walls, where N2 will show cohesive failure within three to five seasons. On an M20 carriageway joint programme we delivered in Kent, the N1 sections we sealed in 2018 are still performing where a small N2 test section, applied on the same slabs at the same time for comparison, failed within four winters. The physical demonstration of the extension difference on identical slabs in identical conditions makes the specification choice obvious.

Technical properties side by side

The BS EN 14188-1 test regime for N1 and N2 covers:

• Cone penetration (indicating sealant hardness at 25°C)
• Resilience (elastic recovery after deformation)
• Softening point (temperature at which sealant begins to flow)
• Flow at elevated temperature (resistance to sag on sloped joints)
• Bond strength to concrete and asphalt substrates
• Extension performance (this is where N1 and N2 diverge significantly)

N1 typically shows higher resilience values and greater bond strength recovery after cyclic extension testing. N2 shows lower resilience and reduced recovery after cyclic loading, which is why it’s classified as low-extension. Both should be selected against manufacturer TDS specifications matched to the project’s calculated movement accommodation requirement.

Application, same process, same discipline

The application process is the same for both grades. The ESA Code of Practice Section 6 covers hot applied sealant application, which applies equally to N1 and N2:

Joint slot preparation. Slots must be sound dense concrete or asphalt, dry, sound, clean and free from frost and dust. Defective or contaminated slot faces are widened until you reach sound material.

Cleaning. Mechanical cleaning (wire brush, grit blast or routing) followed by oil-free compressed air blow-out.

Backer rod. A heat-resistant backer rod suitable for hot applied sealants is caulked into the base of the slot. Standard closed-cell polyethylene rod will melt under hot applied pour, so heat-resistant grade is essential.

Sealant heating. The sealant is loaded into a thermostatically-controlled melter with continuous agitation. Application temperature typically 180 to 200°C, following the manufacturer’s TDS.

Pouring. The sealant is extruded through a heated lance directly into the joint at the correct pour rate.

Sealant recess. The finished sealant level is recessed below the pavement surface. The ESA Code of Practice specifies a minimum 5mm recess for transverse joints under normal vehicle traffic, 7mm for joints wider than 25mm, and 10mm if applied in cold weather. Tolerance is ±2mm.

Cure protection. The joint is protected from traffic until cooled, typically 30 to 60 minutes depending on ambient temperature and pour depth.

We’ve found that contractors who treat N1 and N2 as interchangeable, without matching the grade to the calculated joint movement, produce work that fails predictably. The specification difference is real, and it translates directly into service life.

Standards and compliance

Both N1 and N2 hot applied joint sealants work to:

• BS EN 14188-1 (Type N1 elastic high-extension, Type N2 normal low-extension)
• BS 10948:2020 (application and use of hot- and cold-applied joint sealant systems for concrete pavements)
• SHW Volume 1 Series 1000 (Specification for Highway Works, amended January 2020)
• Highways England Concrete Pavement Maintenance Manual V1.1
• The ESA Code of Practice for Joint Sealing (Issue 3.0, November 2025)

Sectors where each is specified

Highway authorities and Tier 1 contractors are the largest specifiers of both grades. N1 dominates on concrete carriageway joints, motorway and trunk road work, and any pavement subject to full thermal cycling. N2 appears on lower-movement joints and cost-driven maintenance programmes.

Aviation clients specify N1 on taxiway and apron joints. Runway joint work typically moves up to 9525, which is the specialist high-performance aviation specification.

Port operators use hot applied N1 on dockside concrete pavements, though fuel-exposed areas move to two-part cold applied polysulfide or one-part polyurethane rather than hot applied.

Public sector clients including councils and infrastructure operators specify both grades depending on movement requirements and budget.

We’ve delivered hot applied joint sealing using both N1 and N2 on more than 250 UK projects across these sectors in the past six years, with N1 covering roughly 75% of the volume because of the extension range required on modern concrete pavement work.

Specifying N1 or N2 properly

A meaningful hot applied joint sealing specification will identify the grade (N1 or N2), the linear metres, joint dimensions, backer rod type, primer requirement (if any), programme constraints, cooling-window protection, and QC sampling rate. A specification that just lists “hot applied sealant” without grade or movement calculation is incomplete.

If you’re specifying or commissioning hot applied joint sealing work and want to confirm whether N1 or N2 is the right grade for your project, get in touch. We’ll assess the substrate, the movement calculation, the exposure environment, and quote against the actual specification under the ESA Code of Practice. You can see recent project work on our LinkedIn and Instagram.