Master Builders Solutions MasterRoc MP 355 1K
A one-component polyurethane injection resin that reacts with water itself — built to stop active leaks in tunnels, shafts and basements when nothing else will bond.
What is it?
MasterRoc MP 355 1K is a solvent-free, single-component polyurethane injection foam from Master Builders Solutions’ MasterRoc underground-construction range. Unlike most repair resins that need a dry, clean substrate, this one is water-reactive by design — it only foams and cures once it meets moisture, which is exactly the condition you’re fighting when water is pushing through a crack or fissure.
Where is it used?
Underground and below-grade structures carrying active water: metro and road tunnel segment joints, mine shafts and galleries, hydropower headrace tunnels through fissured rock, basement and diaphragm-wall construction joints, lift pits, utility ducts, and any water-bearing void in soil or rock that needs consolidating before excavation continues.
Why use it?
It bonds to wet, running surfaces where conventional resins fail, its reaction speed can be dialled up or down on site with an accelerator, and it keeps curing even if a leak slows mid-injection — so a crew never ends up with a borehole full of unreacted resin.
How is it applied?
The 25 kg resin is dosed with up to 10% of its dedicated MasterRoc MP 355 1K DW accelerator (supplied in 2.5 kg cans) and pumped through a single-component injection pump into packers set in pre-drilled holes; contact with groundwater triggers the foaming reaction inside the crack or void.
About Master Builders Solutions MasterRoc MP 355 1K
Space Arc supplies MasterRoc MP 355 1K to contractors working on India’s metro, highway-tunnel, hydropower and mining programmes — the kind of projects where water doesn’t wait for a dry weekend to show up. It sits within Master Builders Solutions’ MasterRoc Injection range alongside two-component resins such as MP 300 and MP 356, but MP 355 1K is built for a narrower, very common job on site: stopping small-to-mid-volume running water fast, with a single component to manage rather than two reactive parts that have to be metered against each other under time pressure.
The chemistry is straightforward once you see it work. The resin is inert until it touches moisture, at which point it foams and can expand 25 to 30 times its liquid volume, physically displacing water as it fills the crack, joint or fissure and sets into a closed-cell, hydrophobic mass. Crews control how fast that happens by adjusting the dose of its dedicated accelerator and accounting for ground temperature — the manufacturer’s own data shows the reaction starting in as little as 10 seconds at 20°C ground temperature versus around two minutes at 5°C, which is exactly why a short site trial ahead of full-scale injection is standard practice rather than an optional step.
The technical insight
The two numbers that matter most on a live leak are foam expansion (25-30x at a 10% accelerator dose) and reaction time, and MBS publishes both as a function of temperature rather than a single fixed figure — start-of-reaction runs from 120 seconds at 5°C ground temperature down to 10 seconds at 20°C, with the foam fully set anywhere from 50 to 300 seconds later. That spread is the whole point of the separate DW accelerator can: a crew working a cold Himalayan headrace gallery needs a different dosage than one sealing a warm basement joint in Chennai, and the product is designed to be tuned on site rather than used at one fixed ratio.
Where it is used
- Sealing active water ingress through segmental joints in metro, road and rail tunnel linings
- Consolidation and pre-injection grouting of water-bearing rock fissures ahead of TBM or drill-and-blast excavation
- Stopping running leaks in mine shafts, adits and underground galleries
- Sealing construction joints and cold joints in basements and diaphragm walls below the water table
- Curtain and contact grouting in hydropower headrace tunnels and pressure shafts
- Emergency leak control in lift pits, pump rooms and underground utility ducts
- Filling water-bearing voids behind precast tunnel segments and shotcrete linings
- Remedial injection into honeycombed or cracked concrete under active seepage in bridges and culverts
Key advantages
- Reacts specifically with water, so it bonds and cures in exactly the wet, running conditions that stop most other resins from working at all
- Single-component format means one resin can to manage on site, not two reactive parts that must be metered against each other under pressure
- Reaction speed is adjustable through accelerator dosage and can be tuned to ground temperature and water flow rate
- Keeps curing even if a leak slows or dries up mid-injection, instead of leaving unreacted resin sitting inside the borehole
- High foam expansion (25-30x) means one can seals more void than an equivalent volume of a non-foaming grout
- Solvent-free formulation is a genuine safety plus in confined tunnel, shaft and gallery environments
- 24-month shelf life in sealed cans suits the long lead times and remote site stores typical of tunnelling and mining projects
Limitations & considerations
- Built for water-reactive leak-sealing, not structural anchoring — it is not a substitute for a cementitious or epoxy anchoring/bedding grout under machine bases or bearing plates
- Needs a single-component injection pump and a trained crew; it is not a hand-mixed, DIY repair product
- Reaction time is genuinely temperature-sensitive, so the manufacturer’s own data sheet calls for a site trial before committing to full-scale injection
- The published data sheet does not quote an IS/BS/EN compliance number — buyers who need certified test reports for a tender should ask Space Arc for the latest project-specific documentation
- The accelerator is a separate consumable sold in its own 2.5 kg can and must be ordered, stocked and dosed alongside the base resin, not assumed to be bundled in
Selection & best practice
Run a short site trial on reaction time at the actual ground temperature before committing to full-scale injection — the manufacturer’s own tables show start-of-reaction time roughly doubling for every 5°C drop, so a dosage that works in one gallery may be wrong in the next. Flush dry boreholes with water before injecting, since the resin needs moisture to trigger. Keep the pump and hoses filled with non-accelerated resin during short breaks to avoid blockages, and clean equipment with MasterRoc MP 230 CLN (or a water-free oil) immediately after the injection run, before residue sets inside the lines.
Specifications
| Chemistry | Solvent-free, one-component (1K) water-reactive polyurethane injection foam |
| Density (20°C) — resin / accelerator | 1.16 g/cm³ / 0.98 g/cm³ |
| Viscosity (23°C) | 320 mPa·s |
| Colour — resin / accelerator | Brown / clear to yellowish |
| Application temperature | +5°C to +40°C |
| Maximum foam expansion | 25–30x volume (at 10% accelerator dosage) |
| Reaction time (10% water / 10% accelerator) | Start 10–120 sec; complete 50–300 sec, depending on 5–20°C ground temperature |
| Packaging | 25 kg cans (resin) with 2.5 kg cans (MP 355 1K DW accelerator) |
| Shelf life | 24 months in original sealed containers, cool & dry, protected from freezing |
Industry use cases
Metro & rail tunnelling
Injected through packers at segmental lining joints on groundwater-heavy alignments to arrest running water before waterproofing and track-bed work proceeds.
Hydropower & mining
Used for pre-excavation consolidation and curtain grouting in fissured, water-bearing rock ahead of headrace tunnel and pressure-shaft excavation.
Basements & below-grade structures
Applied through drilled injection ports in diaphragm walls, lift pits and basement rafts on high-water-table sites to plug active seepage before the waterproofing membrane goes on.
Utility & culvert rehabilitation
Injected into honeycombed or cracked concrete in ageing culverts and utility ducts where a cementitious grout can’t get a bond on running water.
Underground mining galleries
Deployed for emergency and planned leak sealing in shafts and adits where continued water ingress would otherwise slow face advance.
Frequently asked questions
Will MasterRoc MP 355 1K work on a dry crack?
Is this the same as a structural anchoring or bedding grout?
What equipment does a crew need on site?
How fast does it actually react?
How should we store it, and what’s the shelf life?
Do we need to order the accelerator separately?
How we position Master Builders Solutions MasterRoc MP 355 1K
Within the MasterRoc range, MP 355 1K is the single-component answer to active water ingress; where a crack or joint is dormant rather than leaking, Space Arc typically pairs it with two-component MasterRoc injection resins (MP 300, MP 356) or MasterRoc MSL 345 for broader tunnel waterproofing scope, plus MasterRoc MP 230 CLN as the recommended equipment cleaner. For specifiers working to a Fosroc-standardised BOQ, Fosroc Nitofill PU 1R is a genuine like-for-like — also a single-component, water-reactive polyurethane injection grout for active leaks — and is a reasonable alternative where project specifications or existing site stock already point to the Fosroc Nitofill range.
Fosroc Nitofill PU 1R — Specifiers already standardised on a Fosroc bill of quantities, or holding existing site stock of the Nitofill range, often choose Nitofill PU 1R as the like-for-like single-component, water-reactive PU injection grout for active leaks.
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