Master Builders Solutions MasterRoc MP 355 Thix
The thixotropic water-stopper built for tunnels, shafts and basements where ordinary grouts get washed away
What is it?
A two-component, solvent-free polyurethane injection resin that reacts and expands the instant it meets flowing groundwater, sealing active leaks in seconds rather than minutes.
Where is it used?
Metro and road tunnels, mine shafts, diaphragm walls, basements and dam galleries — anywhere underground structures are fighting high-volume or pressurised water ingress.
Why use it?
Its thixotropic chemistry resists being diluted or washed away by fast-moving water, and it cures into a solid rubber-like mass even in dry cracks, so the injection never fails for lack of water.
How is it applied?
Injected through packers or drilled ports using a two-component metering pump at a 1:1 volumetric ratio, mixed inline through a roughly 50 cm static mixer, with optional accelerators dosed into Part A to tune expansion and set speed.
About Master Builders Solutions MasterRoc MP 355 Thix
MasterRoc MP 355 Thix is a two-component, solvent-free polyurethane injection resin from Master Builders Solutions’ MasterRoc range, built for underground construction’s hardest leak-stopping case: water that is actively flowing, not merely seeping. Ordinary grouts can be diluted or carried away before they set; MP 355 Thix is thixotropic — its viscosity climbs past 4,000 mPa·s within about twenty seconds at 20°C, locking the resin in place before groundwater can wash it out. On contact with water it expands into rigid foam; without water present it still cross-links into a stiff, rubber-like solid, so the injection is never wasted.
That dual-cure behaviour matters on a Delhi Metro tunnel drive through monsoon-fed Yamuna basin alluvium just as much as in a Himalayan hydropower headrace cutting through fractured, water-bearing rock. Supplied as Part A (25 kg cans, 205 kg drums) and Part B (30 kg cans, 250 kg drums) at a straightforward 1:1 volumetric mix, its behaviour is tuned on site with MasterRoc Accelerator 10, 15 or 25, depending on whether the priority is fast water-stopping, dense ground consolidation, or an emergency near-instant set. Space Arc Engineering supplies and applies MP 355 Thix across Delhi NCR project sites, pairing the resin with correct pumping equipment and on-site trial batching.
The technical insight
The chemistry is standard PU injection pushed to an aggressive reaction speed: isocyanate-rich Part A reacts with water — either groundwater or a 2% premix some crews add for extra-fast set — generating CO2 and cross-linked polyurea chains that inflate the resin into a closed-cell rigid foam. Remove the water from the equation and the same chemistry still cross-links Part A and Part B into a dense elastomeric solid, a built-in safety margin most single-purpose water-stopping resins don’t offer. The thixotropic additive package is the other half of the story: it raises apparent viscosity under the low shear of a flowing crack while staying pumpable under the higher shear inside the injection line — exactly the rheology profile needed against a jet of water rather than a damp patch. Expansion factor (roughly 7-20x, accelerator-dependent) and reaction timing are both sensitive to ground and product temperature, which is why the data sheet lists separate start and end-of-foaming times at 10°C, 20°C and 30°C rather than a single number.
Where it is used
- Sealing high-pressure water ingress at TBM segment joints and gaskets in metro and road tunnels
- Arresting active water inflow in mine shafts and drifts during shaft sinking
- Stopping flowing seepage through diaphragm walls, secant piles and basement raft joints
- Sealing leaking construction and cold joints in dam galleries and hydropower headrace tunnels
- Pre-excavation consolidation of loose, water-bearing strata ahead of a tunnel face
- Emergency leak control in operational metro and utility ducts during monsoon groundwater rise
- Contact and curtain grouting behind tunnel linings and shotcrete to close residual voids
- Quick-set water cut-off in deep foundation pits and pile caps during dewatering-critical excavation
Key advantages
- Cures reliably with or without water present, so no injection is wasted on a drier-than-expected crack
- Thixotropic rheology resists dilution and wash-out under fast, high-volume water flow
- Viscosity build past 4,000 mPa·s in 20 seconds locks the resin in place before groundwater can carry it off
- Three dedicated accelerators (10, 15, 25) tune one base resin for rapid stopping, dense consolidation, or emergency ultra-fast set
- Solvent-free formulation is a genuine safety plus in confined tunnel and shaft environments
- Simple 1:1 volumetric mix ratio keeps site batching and pump calibration straightforward
- 24-month shelf life in unopened packs gives project stores realistic buffer stock
- Backed by Space Arc’s Delhi NCR application support and Master Builders Solutions’ global underground-construction track record
Limitations & considerations
- Needs a proper two-component metering pump with a ~50 cm static in-line mixer — not a hand-mixed or cartridge-gun product
- The manufacturer data sheet does not cite a specific IS/ASTM/EN compliance code for this grade — confirm certification needs with your consultant before specifying
- Standard MP 355 Thix is not sold as potable-water certified — where the leak is on a drinking-water structure, the dedicated MP 355 1K DW grade is the correct choice
- Expansion factor and reaction speed shift meaningfully with ground and product temperature, so a site trial batch is strongly advised before full-scale injection
- Uncured resin and accelerators need proper PPE and containment — this is a trained-crew product, not a DIY patch
- Choosing the wrong accelerator (10 vs 15 vs 25) under- or over-shoots the expansion and strength the ground condition actually needs
Selection & best practice
Because reaction speed and foam expansion are both temperature-sensitive, run a small trial injection at the actual ground-water temperature before committing to full-scale work, and keep the static in-line mixer at its recommended length of roughly 50 cm so Parts A and B are fully sheared together before they meet water. Dose accelerators strictly by weight of Part A — 0.5-2% for Accelerator 10 or 15, just 0.1-1% for Accelerator 25 — and shake the can vigorously after adding accelerator (and premix water, if used) so the dose disperses evenly. Between injection breaks, keep Part A circulating through the line, and at the end of a shift flush the pump and hoses completely with MasterRoc MP 230 CLN or a water-free oil before the resin can cure inside the equipment.
Specifications
| Chemistry / system | Two-component, solvent-free polyurethane (PU) injection resin |
| Mixing ratio | 1:1 by volume (Part A : Part B) |
| Part A (20°C) | Yellowish liquid; 320 mPa·s viscosity; 1.00 kg/l density |
| Part B (20°C) | Dark brown liquid; 240 mPa·s viscosity; 1.23 kg/l density |
| Viscosity build-up (20°C) | >2,000 mPa·s at 10 seconds; >4,000 mPa·s at 20 seconds |
| Foam expansion factor | Approx. 7-20x depending on accelerator used |
| Reaction time (with water) | Foaming starts in 20-60 sec, completes in 40-80 sec across 10-30°C |
| Packaging | Part A: 25 kg cans / 205 kg drums; Part B: 30 kg cans / 250 kg drums |
| Shelf life | 24 months, unopened, stored dry between +5°C and +35°C |
Industry use cases
Metro & Underground Rail
Sealing high-volume water ingress at TBM segment joints on tunnel drives through water-bearing strata.
Mining & Shaft Sinking
Stabilising water-bearing ground and arresting flowing inflow during shaft sinking and drift excavation.
Basements & Diaphragm Walls
Stopping pressurised seepage through diaphragm wall joints, secant piles and raft slab construction joints.
Dams & Hydropower
Sealing leaking galleries and headrace tunnel linings against flowing water before permanent repair.
Deep Foundations & Dewatering
Quick-set emergency plugging of active leaks in pile caps and foundation pits during dewatering-critical excavation.
Frequently asked questions
Will MasterRoc MP 355 Thix actually stop water that’s flowing under pressure, or only damp seepage?
How is MP 355 Thix different from MasterRoc MP 355 and MP 355 1K?
What equipment do I need on site to inject this resin?
Which accelerator should I use — 10, 15 or 25?
Is it a problem if the crack turns out to be dry when we inject?
Can this be used on a drinking-water reservoir or potable water structure?
How we position Master Builders Solutions MasterRoc MP 355 Thix
MP 355 Thix sits inside Master Builders Solutions’ broader MasterRoc injection-technology family: pair it with standard MasterRoc MP 355 for calmer water conditions, MP 355 1K or the potable-water-certified 1K DW for single-component jobs, and Accelerators 10, 15 and 25 for expansion or set-speed control, with MasterRoc MP 230 CLN kept on hand purely for flushing pumps and hoses between shifts. Within Space Arc’s own catalogue, Fosroc’s Conbextra GP1, GP2 and GP3 grouts cover general-purpose and precision non-shrink cementitious grouting for baseplates and bearing pads — a genuinely different job to stopping flowing water underground, so they aren’t a substitute here. For a hairline structural crack with no active flow, Fosroc’s epoxy crack-injection systems are the closer comparison; for high-volume or pressurised water ingress in tunnels, shafts and basements, MP 355 Thix remains the more directly matched specification, and Space Arc can advise on the grade and accelerator combination that fits your ground conditions.
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