Fosroc Nitoseal MS600
One-part, isocyanate-free MS polymer sealant engineered for movement joints that sit in water tanks, reservoirs, sewage works and other permanently or intermittently immersed structures.
What is it?
A single-component, medium-modulus joint sealant based on hybrid silyl-modified polyether (MS polymer) technology that cures on atmospheric moisture into a tough, water-resistant elastomer.
Where is it used?
Movement and expansion joints in water-retaining and civil-engineering structures: potable and raw water tanks, reservoirs, sewage tanks, basements, subways, sea walls, parapets and bridge decks.
Why use it?
It holds up under permanent or intermittent immersion, resists dilute acids, alkalis and bacteriological attack, and carries WRAS potable-water approval plus ASTM C920 Class 25 and ISO 11600 F25HM compliance.
How is it applied?
Gun-applied from a 600 ml sachet into a primed joint (Fosroc Primer MS2), tooled flush within five minutes; it skins in around 30-55 minutes and cures at roughly 3 mm per 24 hours.
About Fosroc Nitoseal MS600
Nitoseal MS600 is Fosroc’s engineering-grade answer to a problem most facade sealants quietly avoid: joints that live underwater. Built on hybrid silyl-modified polyether (MS polymer) chemistry, it is a one-part, moisture-curing paste that sets into a tough, elastic rubber capable of taking continuous and pronounced cyclic movement without losing its bond. Because the chemistry is isocyanate-free and 100% solids, there is no shrinkage on cure and no solvent to gas off, which matters when the finished seal has to sit in contact with potable water or aggressive effluent for the life of the structure. It carries WRAS potable-water listing to BS 6920, and conforms to ASTM C920 Type S, Grade NS, Class 25 and ISO 11600 Type F25HM, so specifiers can name it against an international performance line rather than a vague description.\n\nFor Indian water-infrastructure and civil work, that combination is the selling point. A single grade covers the sealing of expansion and construction joints in reservoirs, water and sewage tanks, basements, subways, sea walls, parapets and bridge superstructures, whether the joint is permanently submerged or cycles wet and dry with the tide. It tolerates damp substrates, applies down to +5°C, resists dilute acids and alkalis, and stands up to both aerobic and anaerobic bacteriological attack, all of which are routine in sewage and marine exposure. As an authorised Fosroc distributor and applicator, Space Arc Engineering supplies Nitoseal MS600 with its companion Primer MS2 across Delhi NCR and Pan-India, and can advise on joint design where hydrostatic pressure or immersion timing is involved.
The technical insight
The performance comes from the MS polymer backbone. Unlike a polyurethane, the silane-terminated polyether cures by reacting with atmospheric (or substrate) moisture rather than isocyanate chemistry, so it cross-links cleanly even on damp concrete and releases nothing that would fail a potable-water test. The cured film is medium-modulus, with a Shore A hardness around 32 and elongation above 600%, which is what lets a correctly designed joint absorb its rated 25% movement (as a butt joint) throughout service life without the seal tearing from the arris or splitting internally. The 100% solids formulation means the bead you tool is the bead you keep, so a joint designed to the recommended 2:1 width-to-depth ratio does not lose section as it cures. The one caveat baked into the chemistry is time under water: the seal must reach full cure before it takes permanent immersion, and a minimum cure period is specified before any sea water or sewage contact, because early-age exposure interrupts the moisture cure it depends on.
Where it is used
- Expansion and construction joints in potable and raw water reservoirs and storage tanks
- Joint sealing in sewage treatment tanks and effluent-retaining structures
- Basement, subway and tunnel joints subject to hydrostatic pressure
- Sea walls, tidal and river-wall joints exposed to intermittent immersion
- Parapet, bridge deck and superstructure movement joints
- Joints in civil-engineering structures needing dilute acid and alkali resistance
- Resealing of aged joints in water-retaining concrete after arris preparation
- General building movement joints where a durable, paintable, water-resistant seal is required
Key advantages
- WRAS-listed and approved for contact with potable water to BS 6920
- Complies with ASTM C920 Type S, Grade NS, Class 25 and ISO 11600 F25HM
- Withstands permanent and intermittent immersion, including sewage and marine exposure
- Resistant to aerobic and anaerobic bacteriological attack and to dilute acids and alkalis
- Isocyanate-free, 100% solids chemistry with no cure shrinkage
- Single component yet fast-curing, and can be applied to damp substrates
- Accommodates 25% movement on butt joints and up to 50% on lap joints
- Cures to a tough, elastic seal with excellent UV resistance and ageing performance
Limitations & considerations
- Fosroc Primer MS2 is required for all immersed joints and where substrates may saturate
- Must not be applied below +5°C
- Not suitable for contact with bituminous materials, solvents, oil or petrol
- Must be fully cured, and allowed at least 7 days before sea water or sewage immersion
- Supplied only in grey as standard; other colours are made to order on request
- Good joint preparation cannot be substituted by its adhesion to residual sealant
Selection & best practice
Design the joint before you order the sealant. Nitoseal MS600 suits joint widths from about 5 to 35 mm at a 2:1 width-to-depth ratio, with minimum sealant depths of 5 mm on metal, glass and non-porous faces, 8 mm on porous surfaces and 20 mm where hydrostatic pressure applies. Saw or clean the joint back to sound, dry, frost-free concrete, flush away all slurry, and fit a closed-cell backer rod or bond-breaker tape (a bond breaker is not needed over cellular polyethylene fillers such as Hydrocell XL). Prime the faces with Fosroc Primer MS2, let it become touch-dry, and seal within the primer’s working window. Gun the sealant firmly from the 600 ml sachet and tool it flush within five minutes to force good substrate contact. Protect the finished bead from immersion until it has fully cured, and never expose it to sea water or sewage before the specified minimum cure period has passed.
Specifications
| Chemistry | One-part, moisture-curing hybrid silyl-modified polyether (MS polymer), isocyanate-free |
| Movement accommodation (MAF) | 25% butt joints / 50% lap joints |
| Standards | ASTM C920 Type S Grade NS Class 25; ISO 11600 F25HM; WRAS / BS 6920 potable water |
| Joint width range | 5-35 mm at 2:1 width:depth ratio |
| Skinning time | ~30-55 minutes at 20-23°C / 50% RH |
| Cure rate | Approx. 3 mm in 24 hours (20°C / 50% RH) |
| Hardness / elongation | Shore A ~32; elongation >600% |
| Application temperature | +5°C to +50°C |
| Colour / packaging | Grey (special colours on request); 600 ml sachet, 10 per box; 12-month shelf life |
Industry use cases
Water Supply & Reservoirs
Sealing expansion joints in potable-water tanks and reservoirs where a WRAS-approved, non-tainting seal is mandatory.
Sewage & Effluent Treatment
Joint sealing in STP tanks and effluent structures, using its resistance to anaerobic bacteria and dilute chemical attack.
Marine & Coastal Works
Tidal sea-wall and river-wall joints exposed to intermittent immersion, sealed after the specified pre-immersion cure.
Underground & Below-Grade
Basement, subway and tunnel joints under hydrostatic pressure, detailed to the 20 mm minimum depth for water heads.
Bridges & Infrastructure
Parapet, deck and superstructure movement joints needing durable, UV-stable sealing under climatic extremes.
Frequently asked questions
Can Nitoseal MS600 be used in potable water tanks?
Do I have to prime the joint first?
How much movement can the joint take?
How long before the sealed joint can be submerged?
What pack size and colour does it come in?
Is it different from ordinary facade or silicone sealants?
How we position Fosroc Nitoseal MS600
Nitoseal MS600 is Fosroc’s specialist immersion-grade joint sealant, and it pairs directly with Fosroc Primer MS2, which is mandatory for its wet-service joints. For dry, above-grade facade and cladding movement joints where immersion is not a factor, the lower-cost Fosroc Nitoseal MS (MS100) is the natural sister product, while high-movement or fire-rated details may point to a polyurethane grade. Where a joint filler and backer are needed, Fosroc Hydrocell XL and Expandafoam complete the detail. Across Space Arc’s wider range, immersion sealing sits alongside our waterproofing membranes and PU/crystalline systems for water tanks, and our cementitious and epoxy grouts for the concrete works that surround these joints.
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Authorised distribution, technical advice & professional application across Delhi NCR and Pan-India.