Master Builders Solutions MasterRoc MP 350
A hydrophilic, one-component polyurethane injection resin that reacts with water itself to permanently seal active, water-bearing cracks in underground concrete and rock.
What is it?
A one-component, hydrophilic polyurethane injection resin from Master Builders Solutions’ MasterRoc underground-construction range, formulated to react with moisture and foam into a flexible, closed-cell seal inside active cracks.
Where is it used?
Below-ground concrete and rock structures — tunnel linings, metro shafts, basement and diaphragm walls, water-retaining structures, lift pits, and construction or expansion joints where water is actively entering through a crack or fissure.
Why use it?
It is one of the few resins that cures on contact with water rather than being defeated by it, so contractors can stop an active leak without first drying out or diverting the flow, and the resulting seal stays flexible enough to tolerate minor structural movement.
How is it applied?
Injected neat, or blended with up to 10% MasterRoc MP 350 Accelerator for a faster set in flowing water, through packers with a single-component injection pump — typically alongside MasterFlex 900 hose systems cast into planned joints.
About Master Builders Solutions MasterRoc MP 350
MasterRoc MP 350 is a single-component, hydrophilic polyurethane injection resin from the MasterRoc underground-construction range that Master Builders Solutions built specifically for the below-ground problem most sealants dread: an active, moving crack with water already coming through it. Instead of needing a dry, prepared substrate the way a structural epoxy does, MP 350 is chemically drawn to moisture — on contact with water it foams into a closed-cell, flexible mass that fills the fissure and cures into a permanent seal. At a viscosity of just 250 mPa·s at 23°C, it penetrates hairline fissures down to well under 0.05 mm, which is why it turns up so often in metro tunnel segment joints, diaphragm walls and deep-basement retrofits across Delhi NCR’s underground-rail and infrastructure projects.
On site the product is used much like other hydrophilic PU resins on the market — pumped through packers with a single-component injection pump, with an optional accelerator (up to 10%) dosed in when the water is actively flowing and a faster set is needed. Because it is single-component, there is no mix ratio to get wrong under pressure inside a flooded shaft, which is a genuine practical advantage over two-part systems when crews are fighting live water. Space Arc supplies MP 350 in its standard 210-litre drum and 1,000-litre IBC packs to specialist injection contractors and waterproofing applicators across Delhi NCR and pan-India, typically as part of a planned crack-injection or leak-stopping programme rather than a retail counter purchase.
The technical insight
The chemistry is worth understanding before you specify it. MP 350 is a hydrophilic — water-loving — polyurethane prepolymer; unlike hydrophobic PU foams, which have to physically displace water to react, hydrophilic resins actively react with it, so wetter conditions accelerate rather than inhibit cure. Master Builders Solutions’ own lab data shows this clearly: at 5°C, with 10% accelerator and 10% water, foaming starts around 98 seconds and finishes around 145 seconds; at 20°C the same mix starts foaming in about 30 seconds and finishes around 88 seconds. That temperature sensitivity is exactly why the technical data sheet calls for site trials before full-scale injection — the lab numbers are a guide, not a guarantee, once actual ground temperature and water flow are in play. The low 250 mPa·s viscosity is what gives the resin access to fissures below 0.05 mm, while the resulting closed-cell structure is what makes the finished seal both watertight and flexible enough to ride out the small movements that a rigid epoxy grout can’t absorb.
Where it is used
- Permanent sealing of active, water-bearing cracks in underground concrete structures
- Metro and rail tunnel lining segment joints and shaft leak sealing
- Basement and diaphragm (D-wall) crack and construction-joint leak stopping
- Water-retaining structures — sumps, reservoirs, STP/WTP tanks
- Lift pits and other confined below-grade chambers where drying the substrate isn’t practical
- Rock support and ground-water control injection in tunnelling and mining works
- Upgrading a temporary construction-stage water stop to a permanent seal
- Planned-joint injection via cast-in MasterFlex 900 hose systems
Key advantages
- Single-component — no mix-ratio errors under site pressure, simpler logistics than two-part injection resins
- Hydrophilic chemistry reacts faster in wet conditions instead of being defeated by them
- Low 250 mPa·s viscosity gives access to fissures finer than 0.05 mm
- Cures into a flexible, closed-cell seal that tolerates minor structural movement, unlike rigid epoxy
- Optional accelerator lets the crew tune reaction speed to site water flow and temperature
- Bonds well to damp and actively wet substrates — no need to dry out the crack first
- Applies with standard single-component injection pumps and packers — familiar kit for specialist injection crews
Limitations & considerations
- A specialist pressure-injection product, not a DIY or general-contractor item — needs trained crews and correctly placed packers
- The manufacturer TDS reviewed does not cite an IS/BS/EN compliance standard; specifications requiring code certification should be confirmed with Space Arc before ordering
- Reaction and foam timing are temperature-dependent and can shift meaningfully from lab figures on an actual site — a trial injection is recommended before full-scale work
- It is a flexible water-stop, not a structural or load-bearing grout — it does not replace repair mortars or structural crack-injection epoxies
- Supplied only in bulk 210-litre drums and 1,000-litre IBCs, so it isn’t economical for a single small patch repair
- Needs airtight, cool, dry, frost-free storage and carries a 24-month shelf life — poor site storage discipline can waste unused material
Selection & best practice
Map crack width and water flow before ordering — MP 350’s strength is fine hairline-to-medium fissures with active seepage, not general gap-filling. Drill and set packers at the angle and spacing the injection contractor’s method statement calls for, and always run a small trial mix with the accelerator at the actual site temperature before committing to a full injection programme, since reaction time can shift by a factor of two to three between 5°C and 20°C. Keep drums sealed, stored under cover and protected from frost; once opened, use the batch promptly rather than letting it sit part-used. Wear gloves and eye protection during handling, and keep uncured spillage away from drains as the manufacturer’s safety notes require.
Specifications
| Chemistry / system | Single-component hydrophilic polyurethane injection resin |
| Density (20°C) | 1.15 g/cm³ |
| Viscosity (23°C) | 250 mPa·s |
| Colour | Colourless to yellowish |
| Application temperature | +5°C to +40°C |
| Minimum crack/fissure penetration | < 0.05 mm |
| Shelf life | 24 months, in sealed original packaging, cool & dry, protected from frost |
| Packaging | Part A and Accelerator each supplied in 210-litre drums and 1,000-litre IBCs |
Industry use cases
Metro & underground rail
Segment joint and shaft-lining leak sealing on underground metro and rail tunnelling packages across Delhi NCR.
Basements & diaphragm walls
Stopping active water ingress at construction joints and D-wall panel joints in deep basements of high-rise and commercial projects.
Water & wastewater infrastructure
Crack sealing in sumps, clear-water reservoirs and STP/WTP tanks where taking the structure fully dry isn’t practical.
Lift pits & below-grade chambers
Permanent leak-stopping in lift pits, cable chambers and other confined below-grade spaces.
Tunnelling & ground improvement
Rock support and ground-water control injection on tunnelling and underground mining works.
Frequently asked questions
Is MasterRoc MP 350 the same as an epoxy crack-injection resin?
Can it be injected into a crack with water actively flowing through it?
How fine a crack can it seal?
What equipment does a contractor need to apply it?
How long does the seal last, and what is the shelf life before use?
Is MasterRoc MP 350 hazardous to handle?
How we position Master Builders Solutions MasterRoc MP 350
Within the Master Builders Solutions range on Space Arc, MP 350 sits specifically on the water-stopping side of underground construction — pair it with MasterFlow 648 when the same project also needs a high-strength precision grout for machine foundations or baseplates, or with the MasterEmaco S repair mortar range once an active leak has been stopped and the surrounding concrete needs reinstating. Against other brands, MC-Bauchemie’s MC-Injekt FS is a close chemical cousin — also a single-component hydrophilic PU — and worth comparing on price and lead time for the same application. Where a project specification is standardised on Fosroc-approved materials, Fosroc Nitofill UR63 is a genuine alternative for stopping active leaks, though it is a two-component system rather than MP 350’s single-component format, which changes the on-site mixing and pot-life discipline required.
Fosroc Nitofill UR63 — Specify Nitofill UR63 instead when the project is standardised on Fosroc-approved materials, keeping in mind it is a two-component system rather than MP 350’s simpler single-component format.
Related Waterproofing products
Source Master Builders Solutions MasterRoc MP 350 for your project
Authorised distribution, technical advice & professional application across Delhi NCR and Pan-India.