Master Builders Solutions MasterRoc MP 304
A low-viscosity acrylic gel that chases water through hairline cracks and shuts it off — even while the water is still flowing.
What is it?
A two-component, water-clear acrylic resin injection gel, viscosity close to water, that penetrates hairline cracks and cures into a flexible, re-swellable hydrogel.
Where is it used?
Active water-bearing cracks, joints, and voids in basements, lift pits, retaining walls, tunnel and shaft linings, and masonry.
Why use it?
It seals live, flowing leaks permanently, flexes with minor movement instead of re-cracking, and re-swells to reseal even after drying out.
How is it applied?
Injected 1:1 by volume through packers using a two-component pump with a static in-line mixer; gel time is tuned from 15 seconds to under 4 minutes via hardener dose.
About Master Builders Solutions MasterRoc MP 304
MasterRoc MP 304 is a two-component, water-clear acrylic resin from Master Builders Solutions built for one job: getting into cracks that cementitious grout cannot reach, and shutting off the water moving through them. Thinned almost to the viscosity of water, it is injected through packers at low pressure, travels along hairline cracks and construction joints, then cures into a soft, rubber-like hydrogel that physically blocks the water path. For Delhi NCR and Pan-India basement, metro, and water-infrastructure sites, where high water tables and monsoon ingress are routine, the ability to inject into live, flowing water and still get a sound seal is the whole point.
What earns it a place on tunnel and basement specs is what happens after curing. The gel swells up to 100% of its volume on contact with water, and does this repeatedly: dry it out for a season and wet it again, and it re-swells rather than staying shrunk. Elongation above 950% (mixed with water) — or a firmer, less absorbent gel with the optional Part B — lets it tolerate movement that rigid grouts cannot. It is not a strength-restoring repair material; treat it as the flexible seal injected once the structural repair and drainage detailing are already sound.
The technical insight
The detail worth knowing before ordering: gel time is tunable from about 15 seconds to 3 min 45 sec at 20°C purely by varying the Hardener dose in the water (or Part B) side of the mix. Fast-flowing water under pressure needs a gel that sets in seconds before it washes out; a slow-seeping crack benefits from a slower gel that penetrates further first. Swapping Part B in for plain water trades some elongation for a firmer gel with about 40% water absorption instead of 100% — recommended for expansion-joint and structural crack work. Indian site temperatures run hotter than the 20°C reference, so a trial shot is worth the ten minutes.
Where it is used
- Curtain (pre-)injection ahead of tunnel and shaft excavation to control groundwater ingress before the working face
- Sealing active, water-flowing cracks and construction joints in basements, lift pits, and retaining walls
- Contact grouting and segmental joint sealing behind tunnel linings on metro and rail underground works
- Injection sealing of construction and movement joints in water-retaining RCC tanks and reservoirs
- Stopping minor water inrush through cracks during shaft sinking or deep excavation
- Crack injection in damp or saturated masonry and brickwork with active water passage
- Sealing residual seepage points after a cementitious or epoxy structural repair has rebuilt the section
Key advantages
- Very low viscosity, close to water, penetrates hairline cracks cement-based grouts cannot enter
- Injectable into damp, wet, or actively flowing water — no need to dewater the crack first
- Adjustable gel time (about 15 seconds to under 4 minutes) matches site water-flow conditions
- High elongation (over 950% with water) lets the cured gel flex without re-cracking
- Reversible swelling: re-swells and reseals even after drying out and getting wet again later
- Optional Part B gives a firmer, less water-absorbent gel for expansion joints and structural work
- Cured resin is described as harmless in contact with groundwater once set
- 12-month shelf life in unopened packaging simplifies stocking on Indian project sites
Limitations & considerations
- Not a structural repair material — it seals water, it does not rebuild load-bearing section
- Needs a two-component injection pump with a static mixer and a trained operator, not a hand-mix product
- Gel time and pot life are temperature-sensitive; hot Indian conditions run faster than the 20°C reference
- Concealed injection material only — not a decorative or exposed-surface waterproofing coating
- Results depend on correct packer spacing and drilling pattern; poor layout leaves coverage gaps
Selection & best practice
Premix the full Resin can with its Accelerator, and prepare Part B separately by dissolving the hardener powder into water or MasterRoc MP 304 Part B, dosed per the manufacturer’s table to hit the gel time your water flow demands — run a trial batch first, especially in hot weather, since Indian temperatures shorten both gel time and the roughly 5-hour pot life. Inject the two activated components 1:1 by volume through a proper two-component pump with a static in-line mixer and correctly spaced packers, and use Part B instead of plain water for expansion-joint renovation or structural crack injection.
Specifications
| Chemistry | Two-component acrylic resin injection gel |
| Resin appearance / viscosity (20°C) | Clear liquid, 55 mPa·s |
| Resin density (20°C) | 1.22 kg/l |
| Mixed material density (20°C) | 1.16 kg/l |
| Gel time (20°C) | Adjustable, 15 seconds to 3 min 45 sec |
| Elongation at break | >950% (with water) / >700% (with Part B) |
| Water absorption of cured gel | ~100% (with water) / ~40% (with Part B) |
| Mixing ratio | Resin (+Accelerator) : Part B = 1:1 by volume |
| Pack sizes | Resin 20 kg can; Accelerator 0.5 kg can; Hardener 1.0 kg can; optional Part B 20 kg can |
Industry use cases
Metro and underground rail construction
Curtain injection ahead of TBM drives and segmental joint sealing to control groundwater ingress.
Basement and lift-pit waterproofing
Sealing active seepage through construction joints and cracks without dewatering the structure.
Water and wastewater infrastructure
Crack and joint injection in RCC tanks, reservoirs, and STP/WTP structures under pressure.
Industrial and commercial basements
Sealing leaking joints in factory and warehouse retaining walls in high water-table zones across Delhi NCR.
Frequently asked questions
Can MasterRoc MP 304 be injected into a crack with water actively flowing through it?
What’s the difference between mixing MP 304 with water versus with Part B?
How do I control how fast the gel sets on site?
Is MasterRoc MP 304 a structural repair material?
What equipment does the applicator need?
How long can unused material be stored on site?
How we position Master Builders Solutions MasterRoc MP 304
Space Arc is introducing MasterRoc MP 304 as the entry point into the wider MasterRoc underground-construction range from Master Builders Solutions (now under Sika’s ownership) — ask about the rest of the range for tunnel- or shaft-scale work. On site it pairs naturally with our MasterEmaco repair mortars and MasterFlow precision grouts: rebuild lost section first, then use MP 304 to shut off any live water still finding its way through. Specifiers benchmarking acrylic and polyurethane injection resins sometimes also evaluate Fosroc’s injection-resin range for the same role; the practical choice usually comes down to which principal’s local technical support the contractor already trusts.
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