Fosroc Nitoseal Primer MS2
Two-component solvent-based epoxy primer that locks Fosroc’s Nitoseal MS-polymer sealants onto concrete in high-movement and water-immersed joints.
What is it?
A two-component, solvent-based epoxy-resin primer used to prepare joint faces before applying Fosroc’s Nitoseal MS-polymer sealant range (MS300, MS600, MS60 and PU800). It is a joint-treatment ancillary, not a sealant itself.
Where is it used?
Concrete and porous masonry joint arrises that will see high movement or intermittent/permanent water immersion – water-retaining structures, basements, podiums, plant rooms, plinths and external pavement joints.
Why use it?
It chemically keys the MS-polymer sealant to the substrate so adhesion survives joint cycling and saturation. Without it, MS sealants can peel or debond on demanding, wet or high-movement joints.
How is it applied?
Pour the hardener tin fully into the base tin, shake for 2 minutes, then brush a thin even coat onto clean, dry, sound joint faces. Apply the Nitoseal sealant between 30 minutes and 4 hours after priming.
About Fosroc Nitoseal Primer MS2
Fosroc Nitoseal Primer MS2 is a purpose-made adhesion primer rather than a stand-alone joint sealant. It is the partner product that prepares the joint faces before Fosroc’s silyl-modified-polymer (MS-polymer) sealants – principally Nitoseal MS300 and Nitoseal MS600, and also Nitoseal MS60 and the polyurethane Nitoseal PU800 – are gunned into the joint. Supplied as a two-part, solvent-based epoxy-resin system (a base and a hardener), it is engineered for the situations where MS-polymer sealants are most likely to be challenged: joints that flex heavily through their service life and joints that are intermittently splashed or permanently immersed in water. On a dry, low-movement internal joint many MS-polymer sealants can be applied unprimed, but as soon as the joint is wet, saturated or working hard, a dedicated primer is what keeps the sealant bonded. That is the job MS2 does. For Indian projects the product reaches site as imported Fosroc stock, and because it is a reactive two-pack epoxy with a strict overcoat window, it rewards crews who understand joint-sealing discipline. Space Arc Engineering supplies it as a system alongside the matching Nitoseal sealant, backing rod and tooling so the specified bond is achieved on the first attempt rather than chased through warranty call-backs. As an authorised Fosroc distributor and applicator across Delhi NCR and Pan-India, we can also advise on whether a given joint genuinely needs MS2, a different Fosroc primer, or no primer at all.
The technical insight
The critical detail with MS2 is its overcoat window. It is a reactive two-component epoxy primer: once the hardener is shaken into the base it begins curing, and Fosroc’s instruction is to apply the sealant between 30 minutes and 4 hours after priming. Under 30 minutes the solvent has not flashed off and the film is not yet tacky-keyed; beyond roughly 4 hours the primer film has cured too far to develop a chemical bond with the incoming sealant, and the only remedy is to mechanically remove the film by grinding or grit-blasting and re-prime. This is why MS2 is not interchangeable with simple wipe-on adhesion promoters. Because it is solvent-based it is also highly flammable, so it must be used with ventilation and away from ignition sources, and the pack must not be split – the base-to-hardener ratio is fixed by the supplied tins. The chemistry is deliberately matched to silyl-modified polyethers, so MS2 should be paired only with the Nitoseal products Fosroc names for it; using it under an unrelated polysulphide or pure-PU sealant from another system is outside its design intent.
Where it is used
- Priming concrete expansion and movement joints before Nitoseal MS300 or MS600 in water-retaining structures (tanks, reservoirs, STP/ETP, sumps)
- Priming joints in basements, podiums, lift pits and plant rooms that are subject to standing water or repeated saturation
- Preparing high-movement joints in external pavements, hardstandings and decks before MS-polymer sealing
- Priming joint faces on bridge approaches, retaining walls and below-grade structures where immersion is intermittent
- Sealing-system bond enhancement on porous concrete and masonry arrises where unprimed MS adhesion would be marginal
- Joint treatment ahead of Nitoseal MS60 and Nitoseal PU800 on demanding civil and industrial joints
Key advantages
- Two-pack epoxy chemistry gives a genuine chemical key, not just a surface wipe, so adhesion survives immersion and cyclic movement
- Specifically formulated for Fosroc’s Nitoseal MS-polymer range, removing guesswork about primer/sealant compatibility
- Simple field mixing – pour hardener into base and shake for two minutes, no separate measuring
- Brush application onto the joint arris is fast and needs no specialist plant
- Targets exactly the conditions (high movement, immersion, saturation) where unprimed MS sealants are most likely to fail
- Supplied as a balanced complete pack so the mix ratio is always correct on site
Limitations & considerations
- It is a primer only – it provides no sealing, gap-filling or waterproofing function on its own
- Strict overcoat window: seal between 30 minutes and 4 hours; miss it and the film must be ground/grit-blasted off and re-primed
- Solvent-based and highly flammable, requiring ventilation, no naked flame, and careful storage
- Two-pack reactive system has a limited pot life once mixed, so it cannot be part-used and kept
- Pack must not be split – the base-to-hardener ratio is fixed and cannot be hand-proportioned
- Substrate must be clean, sound and dry at the moment of priming; it will not bond over dust, laitance, oil or standing moisture
- Matched to specific Nitoseal sealants – not a universal primer for unrelated sealant chemistries
Selection & best practice
Treat priming as part of joint design, not an afterthought. First confirm the joint actually warrants MS2 – it is intended for high-movement and immersed/saturated joints; many dry internal MS-polymer joints can be sealed unprimed per Fosroc’s guidance, so check the sealant TDS before buying primer. Prepare the joint properly: faces must be sound, clean and dry, with laitance, dust, curing compound and oil mechanically removed, and a closed-cell backer rod or bond-breaker tape installed so the sealant bonds on two faces only and is free to move. Respect the classic joint geometry for the chosen Nitoseal sealant – typically around a 2:1 width-to-depth ratio for movement joints, within the sealant’s stated minimum and maximum widths and its movement accommodation factor. Then prime: shake the combined pack for a full two minutes, brush a thin, even coat onto the joint faces only (avoid flooding or puddling), and gun the sealant within the 30-minute-to-4-hour window. If that window lapses, do not seal over it – grind or grit-blast the primer off and re-prime. Keep the work ventilated and clear of ignition sources, and always read the current Fosroc TDS and SDS for the exact sealant being used.
Specifications
| Product type | Two-component, solvent-based epoxy-resin joint primer |
| Function | Adhesion primer for Fosroc Nitoseal MS-polymer / PU sealants (not a sealant) |
| Compatible sealants | Nitoseal MS300, Nitoseal MS600, Nitoseal MS60, Nitoseal PU800 |
| Components | Base + hardener supplied as a matched, non-splittable pack |
| Mixing | Empty hardener fully into base, shake at least 2 minutes |
| Application method | Brush onto clean, dry, sound joint faces |
| Overcoat window | Apply sealant between 30 minutes and 4 hours after priming |
| Indicative coverage | ~90 m of joint per 0.75 litre pack (Fosroc literature) |
| Pack sizes | 500 ml / 750 ml complete two-pack units (regional availability) |
| Primary substrate | Concrete and porous masonry joint arrises |
| Service condition | High-movement joints; intermittent or permanent water immersion / saturation |
| Flammability | Highly flammable – solvent-based; keep from ignition sources, ventilate |
Industry use cases
Water & wastewater
Priming expansion and construction joints in RCC water tanks, reservoirs, STP/ETP basins and clear-water sumps before Nitoseal MS300/MS600, where joints are permanently immersed.
Basements & below-grade
Preparing joint faces in basements, lift pits and tank rooms subject to standing water or hydrostatic saturation, ensuring the MS-polymer seal stays bonded under wetting.
Infrastructure & civil
Treating high-movement joints on bridge approaches, retaining walls and below-grade structures where immersion is intermittent and movement is severe.
Industrial & plant
Priming floor and plinth joints in plant rooms, pump houses and wash-down areas before MS-polymer or PU sealing in saturated environments.
Pavements & external decks
Keying MS sealants into porous concrete pavement, hardstanding and podium-deck joints that flex heavily and see repeated water exposure.
Frequently asked questions
Is Nitoseal Primer MS2 a sealant?
Which Fosroc sealants need MS2 primer?
Do I always have to prime before using an MS-polymer sealant?
How long after priming can I apply the sealant?
How do I mix it?
Is it safe to use indoors?
How we position Fosroc Nitoseal Primer MS2
Within the Fosroc system, Nitoseal Primer MS2 sits beside the Nitoseal MS-polymer sealants it serves – Nitoseal MS300, MS600 and MS60 – and the polyurethane Nitoseal PU800, rather than competing with them; it is the enabling primer, while Thioflex 600 (two-part polysulphide) and Colpor 200PF (for pavement and trafficked joints) cover other joint chemistries in the same family, each with its own primer regime. Compared with rival sealant systems, the closest equivalents are the priming products that accompany Sika’s Sikaflex range, MBCC/Master Builders Solutions’ MasterSeal joint sealants, and STP’s Indian sealant lines – all of which similarly call for substrate-specific primers on demanding or immersed joints. MS2 is not a general-purpose primer and should not be cross-used under another manufacturer’s sealant; its value is in being precisely matched to Fosroc’s MS-polymer chemistry. As an authorised Fosroc distributor and applicator in Delhi NCR and Pan-India, Space Arc Engineering supplies MS2 as part of a complete, compatible joint-sealing package and advises honestly when a joint needs it, needs a different Fosroc primer, or needs no primer at all.
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