Fosroc Nitoseal PU12 formerly Nitoseal 12
Two-part polyurethane joint sealant engineered for water-retaining structures, sewage treatment works and tidal sea defences, supplied and applied by Space Arc Engineering across Delhi NCR and Pan-India.
What is it?
A two-part, elastomeric polyurethane joint sealant (base plus curing agent) that cures by chemical reaction into a tough, rubber-like seal resistant to bacteriological attack, immersion and abrasion.
Where is it used?
Movement and expansion joints in water-retaining and water/wastewater structures: sludge digestion tanks, filtration and aeration tanks, culverts, raw water reservoirs and concrete sea walls subject to tidal scour.
Why use it?
It withstands aerobic and anaerobic bacteriological conditions and continuous immersion that defeat ordinary gun-grade sealants, while a separate accelerator lets crews seal sea-defence joints between tides.
How is it applied?
Joints are cleaned and dried, a bond-breaker tape is laid at the base, sides are primed (Fosroc Primer 7 on porous, Primer 4 on non-porous), the two parts are paddle-mixed, then gunned in and tooled to a smooth finish.
About Fosroc Nitoseal PU12 formerly Nitoseal 12
Fosroc Nitoseal PU12, formerly catalogued as Nitoseal 12, is a two-part elastomeric joint sealant built on polyurethane chemistry. It is supplied as a base compound and a curing agent pre-batched in the correct ratio; once the two are mixed they react chemically and set to a tough, rubber-like solid that bonds well to most common construction substrates. Unlike everyday gun-grade facade sealants, PU12 was developed specifically for the water industry, where the joint has to survive permanent or cyclic immersion, biological attack and physical scour rather than just weathering and UV.
The product addresses a problem that consultants and water-board engineers in India know well: sealants in sewage and water-treatment assets are exposed to bacteriological environments, silt build-up in storage, and in coastal works the relentless abrasion of tidal water. Nitoseal PU12 is formulated to resist both aerobic and anaerobic bacteriological conditions normally found in sewage treatment works, to adhere reliably under immersed conditions, and to take abrasion in concrete sea walls subject to tidal scour. A separate accelerator component can be stirred in at mixing so that, at 10 degrees C, the seal can take tidal immersion roughly 60 minutes after application without damage, letting contractors complete a joint within a single low-tide window.
For Space Arc Engineering clients, Nitoseal PU12 sits in the specialist water-and-effluent corner of the Fosroc sealant range. It is a chemical-cure, immersion-grade polyurethane rather than a general-purpose or facade product, and it should be specified where the design driver is biological and immersion resistance. Where it physically fits in a typical reservoir or tank wall is illustrated by Fosroc’s own detail, in which PU12 is used in combination with Hydrocell XL backer, a Supercast Hydrofoil waterstop and a Nitoseal MS600 cap on the dry face.
The technical insight
The defining number for any movement-joint sealant is its movement accommodation factor (MAF). Nitoseal PU12 carries a verified MAF of 20% in butt joints, which directly governs joint design: the seal width must be sized so that the expected thermal and structural movement stays within plus or minus 20% of the as-installed width. PU12 is a chemical-cure system, not a moisture-cure or solvent-release one, so cure proceeds through the full depth at a known rate (48 hours at 25 degrees C, 96 hours at 10 degrees C), and permanent immersion must wait until full cure unless the accelerator is used to roughly halve those times. Cured hardness is Shore A 35 to 40, soft enough to absorb cyclic movement yet firm enough to resist abrasion and silt. Because PU12 is a two-part pour-and-tool grade rather than a cartridge gun-grade, the correct primer is essential, not optional: Fosroc Primer 7 on porous concrete and Fosroc Primer 4 on non-porous substrates, with the sealant applied in the 30-minute-to-3-hour window after priming.
Where it is used
- Movement and expansion joints in raw-water reservoirs and water-retaining concrete structures
- Sludge digestion tanks, filtration tanks and aeration tanks in sewage and effluent treatment plants
- Culverts and buried water-conveyance structures
- Expansion joints in concrete sea walls and coastal defence works subject to tidal scour
- Construction and movement joints under permanent or cyclic immersion where biological resistance is required
- Joints in tidal zones where the accelerator allows sealing to be completed between tides
Key advantages
- Resistant to both aerobic and anaerobic bacteriological attack typical of sewage treatment works
- Excellent adhesion under immersed and continuously wet conditions
- High abrasion resistance, suiting tidal-scour and silt-laden environments
- Optional accelerator component lets crews complete joints between tides (immersion approx. 60 minutes after application at 10 degrees C)
- Chemical-cure, 100% solids polyurethane with no solvent shrinkage on cure
- Bonds well to most common construction substrates when correctly primed
- 20% movement accommodation factor in butt joints for genuine movement-joint duty
Limitations & considerations
- Two-part product requiring accurate on-site mixing with a slow-speed drill and Fosroc mixing paddle; not a ready-to-use cartridge
- Mandatory priming, Fosroc Primer 7 (porous) or Primer 4 (non-porous), with a strict 30-minute-to-3-hour re-coat window
- Modest 20% MAF in butt joints, lower than premium low-modulus PU/MS sealants, so wider joints are needed for high-movement applications
- Permanent immersion must wait for full cure (48 h at 25 degrees C, 96 h at 10 degrees C) unless accelerator is used
- Application temperature limited to 5 to 50 degrees C; cure slows markedly in cold conditions
- Single supply colour (grey); not intended as a decorative or facade sealant
- Soft foam back-up must not be used; only polyethylene bond-breaker tape at the joint base
- Primers and equipment cleaner are highly flammable and need controlled storage and handling
Selection & best practice
Design the joint around the 20% MAF: size the as-installed width so anticipated movement stays within plus or minus 20%, and form the slot accurately so the seal depth matches the manufacturer’s guide (for example 25 x 15 mm or 50 x 25 mm w x d). Always insert a self-adhesive polyethylene bond-breaker tape at the base so the sealant moves on two faces only, and never substitute soft foam back-up. Ensure the joint is dry, clean and frost-free, and that expansion-joint filler is tightly packed with no voids at the base of the slot. Prime correctly for the substrate (Primer 7 on porous concrete, Primer 4 on non-porous) and respect the 30-minute-to-3-hour application window, re-priming any surface left longer than 3 hours. Mix the full base and curing agent for at least 4 minutes to a uniform streak-free colour; add the accelerator only where a tidal or fast-cure window demands it. Gun the sealant into the primed joint, tool off smooth, remove masking immediately and avoid excessive tooling that causes surface drag. In tidal work, incorporate the accelerator and complete sealing at least one hour before immersion at 10 degrees C.
Specifications
| Product type | Two-part elastomeric polyurethane joint sealant |
| Former name | Nitoseal 12 |
| Form | Two-part compound; base white paste, curing agent dark-grey paste |
| Cure mechanism | Chemical cure |
| Solids content | 100% |
| Density | 1.44 kg/litre |
| Colour | Grey |
| Movement accommodation factor | 20% in butt joints |
| Hardness, Shore A at 25 degrees C | 35 to 40 |
| Application temperature | 5 degrees C to 50 degrees C |
| Pot life at 25 degrees C | 2 to 3 hours (20 minutes with accelerator) |
| Cure time | 48 hours at 25 degrees C; 96 hours at 10 degrees C (approx. 50% faster with accelerator) |
| Primers required | Fosroc Primer 7 (porous surfaces); Fosroc Primer 4 (non-porous surfaces) |
| Biological resistance | Good resistance to aerobic and anaerobic conditions in sewage treatment |
| Flammability | Burns but does not readily support combustion; non-flammable |
| Pack size | Carton of 4 x 2.0 litre units; accelerator 50 ml tin (one per 2 litre tin) |
| Coverage example | 25 x 15 mm joint = 0.375 litre/m (approx. 5.3 m per 2 litre) |
| Storage life | 12 months in original containers, 5 degrees C to 27 degrees C, cool and dry |
Industry use cases
Municipal water supply
Sealing movement and expansion joints in raw-water reservoirs and treated-water reservoirs where the sealant must adhere under permanent immersion and resist silt accumulation.
Sewage and effluent treatment
Joint sealing in sludge digestion, filtration and aeration tanks where aerobic and anaerobic bacteriological attack would degrade ordinary sealants.
Coastal and marine defence
Movement joints in concrete sea walls subject to tidal scour, using the PU12 accelerator so sealing is completed within a single low-tide window.
Drainage and conveyance infrastructure
Sealing joints in culverts and buried water-conveyance structures that experience cyclic wetting, flow abrasion and silting.
Industrial water and process plants
Joints in process water tanks and containment structures where immersion service and chemical/biological exposure demand a dedicated immersion-grade PU sealant.
Frequently asked questions
Is Nitoseal PU12 the same as the old Nitoseal 12?
What is the movement accommodation factor (MAF) of Nitoseal PU12?
Does Nitoseal PU12 need a primer?
Can Nitoseal PU12 be used under water and in sewage tanks?
How long does Nitoseal PU12 take to cure?
What pack sizes and colour are available?
How we position Fosroc Nitoseal PU12 formerly Nitoseal 12
Within the Fosroc sealant family, Nitoseal PU12 is the specialist immersion-and-biological-resistance polyurethane, distinct from the everyday Nitoseal range: the silyl-modified Nitoseal MS600/MS300 are gun-grade facade and construction-joint sealants, while two-part polysulphide Thioflex 600 and the hot-applied Colpor 200PF target trafficked pavement and general civil joints. PU12 is the one to specify when the governing requirement is permanent immersion, sewage-grade bacteriological attack or tidal scour rather than UV and weathering, and it is commonly detailed alongside Hydrocell XL backer rod, Supercast waterstops and a Nitoseal MS600 dry-face cap. Credible alternatives an engineer may evaluate include Sika’s Sikaflex range and Sikadur combination joint systems for water structures, MBS (Master Builders Solutions) MasterSeal polyurethane sealants, and STP/Pidilite immersion-grade joint sealants; the right choice depends on the specified MAF, immersion duration and applicable standard. As an authorised Fosroc distributor and applicator, Space Arc Engineering can confirm current availability, advise on primer and accelerator requirements, and supply Nitoseal PU12 with the matching Fosroc Primer 4/7 and ancillaries across Delhi NCR and Pan-India.
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