About Master Builders Solutions MasterRoc MP 358 GS

MasterRoc MP 358 GS is Master Builders Solutions’ underground-construction-grade polyurethane injection resin — not a general building grout, but a specialist rock and coal consolidation system used by tunnelling and mining engineers worldwide. Chemically it is a two-component, solvent-free, hydrophobic PU: Part A (yellow, 300 mPa·s) and Part B (dark brown, 240 mPa·s) meet through a static in-line mixer, gel in roughly 65 seconds, and expand up to 1.5 times in volume to lock into fracture networks as fine as 0.14 mm. That combination of speed, controlled expansion, and near-zero sensitivity to water contact is what separates it from the cementitious or epoxy grouts used in surface construction, and why it sits in a different part of the catalogue from products like anchor or bedding grout.

For Indian projects — metro tunnel drives in Delhi-NCR and other cities, Himalayan hydropower headrace and tailrace tunnels, and coal-belt roadways across Jharkhand, Odisha and Chhattisgarh — this is the material engineers reach for when a fractured face or a water-bearing seam threatens the shift’s advance rate. Space Arc Engineering supplies MasterRoc MP 358 GS as part of its Master Builders Solutions underground-construction range, alongside the injection pumps, static mixers, cleaning agent and PPE needed to run it safely on site. It is priced and packaged as a specialist consumable rather than a bulk commodity grout, so we scope it against actual fracture volume and expected injection rate rather than square-metre coverage, and we talk through pump compatibility before a drum ever reaches site.

The technical insight

The figure worth watching on the data sheet is “border time” — under 10 minutes to reach 1 MPa adhesive strength under lab conditions — because that is what actually governs how soon a crew can safely resume drilling or advance the face, more than the headline gel time does. The 65-second gel time and ≤1.5 foam expansion factor are both products of the A:B reactivity, which is why mixing accuracy through the recommended ~32 cm static in-line mixer matters more here than with slower two-part epoxy grouts: a poorly proportioned or poorly mixed shot will gel on schedule but simply won’t reach the stated 9 N/mm² flexural adhesive strength, and there is no practical way to detect that failure until the ground moves again.

Where it is used

• Consolidating fractured rock ahead of shotcrete or final lining in drill-and-blast and TBM tunnel headings
• Stabilising broken coal in underground development roadways and longwall gate roads
• Sealing active water and gas ingress through fissured rock before excavation continues
• Pre-support grouting ahead of rock bolting in weak, blocky or fractured ground
• Filling voids and cavities behind tunnel linings and shotcrete in broken strata
• Emergency face stabilisation where sudden water inflow or rockfall risk halts advance
• Portal and shaft-collar consolidation in weathered or fractured rock at tunnel entries
• Ground treatment ahead of a TBM cutterhead through mixed-face or fractured zones

Key advantages

• Reacts in roughly a minute (gel 65s ± 10s, hardening 70s ± 10s at 25°C), so injection rounds keep pace with an advancing tunnel or mine face
• Expands up to 1.5x its own volume without needing water contact, filling irregular fracture networks a thin cementitious grout would bypass
• Penetrates cracks wider than 0.14 mm, reaching fine fissures beyond the practical range of most cement-based systems
• Low sensitivity to water and good bonding on wet or damp rock and coal surfaces, with almost no reaction-temperature spike on water contact
• Delivers over 9 N/mm² flexural adhesive strength at 7 days — genuine structural consolidation, not just void filling
• Solvent-free formulation, a real safety advantage in the confined, poorly ventilated headings typical of underground work
• Straightforward 1:1 by-volume mixing ratio through a static in-line mixer keeps pump operation simple for trained crews
• 24-month shelf life when stored correctly, useful for remote mine or hydro-tunnel sites with long resupply lead times

Limitations & considerations

• Needs a dedicated two-component injection pump with a static in-line mixer — it cannot be hand-mixed and poured like a conventional grout
• The fast gel window leaves little margin for error; any pause in pumping must be managed immediately or the mixer will block
• Both components need storage between +5°C and +35°C, ideally warmed above 15°C before use, which takes planning on sites without climate-controlled stores
• Not a substitute for cementitious anchor, bedding or machine-base grout — using it for routine anchoring is over-specification and needlessly expensive
• Uncured resin is a skin and eye irritant and must be kept out of drains and watercourses, so proper PPE and spill containment are non-negotiable
• Cost per litre sits well above standard construction grouts, so it only pays off where the reaction speed and fine-crack penetration actually matter

Selection & best practice

Specifications

Industry use cases

How we position Master Builders Solutions MasterRoc MP 358 GS

MasterRoc MP 358 GS sits in Master Builders Solutions’ underground-construction (MasterRoc/MEYCO) injection range alongside MasterRoc MP 358 SC — a more reactive, lower-foam-factor sibling for tighter fracture control — plus MasterRoc MP 355 Thix and MP 367 Foam for different reactivity and expansion profiles, and MasterRoc MP 230 CLN, the dedicated cleaning agent every site running these resins should keep in stock. There isn’t a genuine Fosroc equivalent worth recommending here: Fosroc’s Indian catalogue is built around surface construction chemicals — Renderoc repair mortars, Conbextra grouts, Nitoseal joint sealants — rather than mining- and tunnelling-grade PU strata consolidation resins, so specifiers comparing options typically look instead at specialist underground-construction suppliers such as Minova/Carbotech or Normet. Space Arc can advise on the right MasterRoc variant and injection equipment for a given fracture profile and project type.

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