About Master Builders Solutions MasterRoc MP 355

MasterRoc MP 355 is Master Builders Solutions’ twin-pack, solvent-free polyurethane injection resin built for one specific, hard problem: water that will not stop moving. Component A (a lighter brown liquid) and Component B (a denser, dark brown liquid) are injected 1:1 by volume through a static in-line mixer; on contact with groundwater the mix expands rapidly into a rigid, closed-cell foam that chases and blocks the flow path, while in dry ground it simply cures to a tough, rubber-like solid. That dual behaviour — the resin always cures, whether or not water shows up — is its core engineering value, and it is why Master Builders Solutions places it under the MasterRoc range for tunnelling, mining and underground water management rather than in its general-purpose grout lines.

What sets MP 355 apart on a live site is its accelerator system. The same base resin can be dosed with Accelerator 10 for a fast, high-expansion foam aimed purely at cutting off running water, Accelerator 15 for a denser, higher-strength foam when the goal is ground consolidation rather than just sealing, or Accelerator 25 when a large, uncontrolled volume of water demands a strong foam that will not wash out. That range means one product, correctly dosed, can carry a tunnel or basement crew from an emergency active leak through to permanent structural ground improvement — provided the applicator respects the exothermic-reaction volume limits Master Builders Solutions publishes for each drill-hole length.

The technical insight

MP 355’s underlying chemistry is a moisture-cross-linking polyurethane prepolymer split across two ready-to-use components. Component A, the lighter 1.00 kg/L brown liquid, carries the reactive isocyanate backbone; Component B, the denser 1.24 kg/L dark liquid, is the co-reactant that drives cure even when no groundwater is present. That dual pathway is the real engineering trick — most single-component PU injection resins depend entirely on ambient moisture to start reacting, which can leave dry pockets under-cured, whereas MP 355’s two-component design cures on its own and simply reacts faster, with CO2-driven foam expansion, if it meets water. The three accelerators are essentially catalyst packages that dial the foam factor: Accelerator 10 pushes expansion to 20-25 times the injected volume, a fast, high-volume foam suited to chasing and sealing running water; Accelerator 15 restrains expansion to 7-9 times for a denser, higher-strength foam suited to load-bearing ground improvement; Accelerator 25 is premixed into Component A when large, uncontrolled water volumes are expected and a strong, low-expansion foam is needed to resist washout. Because the reaction is exothermic, Master Builders Solutions caps single-shot injected volumes by drill-hole length — for example, a maximum of about 220 litres of mixed material for a 4-9 m hole — an operational detail that matters more than most specifiers assume, since treating this as a simple “inject and walk away” grout risks overheating the resin in a confined hole.

Where it is used

• Cut-off grouting for active, flowing water ingress in tunnels, shafts and metro/underground station excavations
• Ground consolidation of fractured rock and water-bearing sands, gravels and landfill material ahead of excavation
• Void filling behind tunnel linings, segments and retaining structures
• Emergency injection to stop active seepage through basement walls, diaphragm walls and lift pits
• Sealing leaking construction joints and honeycombed concrete where flowing water defeats epoxy or cementitious grout
• Manhole and sewer chamber groundwater infiltration repair
• Pre-treatment consolidation grouting ahead of TBM drives and rock-bolting programmes

Key advantages

• Reacts and cures whether or not it meets water, so there are no under-cured dry pockets the way there can be with purely moisture-triggered one-component resins
• Switches behaviour automatically — rigid closed-cell foam against flowing water, a stiff rubber-like solid in dry ground — from a single injected chemistry
• Three accelerators (10 / 15 / 25) let one base resin cover both fast water cut-off and structural ground improvement, instead of stocking two different products
• Solvent-free formulation, which matters for air quality and safety in confined tunnel, shaft and manhole work
• Fast-reacting, so it can be used for emergency active leaks where cementitious grout cure times are not an option
• 24-month shelf life in unopened, correctly stored packs suits phased tunnel, metro and mining programmes with staggered resin consumption
• Documented accelerator dosage tables and injection volume limits give the applicator a clear procedure instead of trial-and-error dosing

Limitations & considerations

• Needs a twin-component injection pump with a static in-line mixer — this is not a hand-mix, pour-in product
• The reaction is exothermic, so single-shot injected volume must be capped to Master Builders Solutions’ drill-hole-length table, or the resin can overheat and smoke
• Reaction speed is sensitive to resin, rock and groundwater temperature, so a field trial shot is recommended before full-scale injection
• Component B is noticeably denser than Component A, so pump calibration must be checked regularly to hold the correct 1:1 volume ratio
• The standard two-component grade is not drinking-water certified; that requires a different variant in the MP 355 family
• The technical data sheet reviewed for this page is published for the US/Canada market — confirm current India stock, batch documentation and any local approvals with your Space Arc representative before specifying it into a tender BOQ

Selection & best practice

Specifications

Industry use cases

How we position Master Builders Solutions MasterRoc MP 355

MasterRoc MP 355 sits within Master Builders Solutions’ broader MasterRoc range for tunnelling, mining and underground water management, alongside rock-bolting resins, sprayed-concrete admixtures and other injection chemistries under the same brand. Where a job calls for a single-component, moisture-triggered resin instead of a twin-pump two-component system — smaller infiltration points, tighter access, or a potable-water-contact requirement — ask your Space Arc representative about the single-component MP 355 variants in the family before defaulting to this standard two-component grade. For specifications written to a Fosroc-only vendor list, Nitofill PU23 is the closest genuine equivalent in our catalogue: a similarly solvent-free, two-component PU injection resin for active-leak sealing and ground stabilisation, with the decision between the two usually coming down to brand approval and local stock rather than chemistry.

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