MC-Bauchemie MC-Fast ST
MC-Bauchemie’s ready-to-use cementitious plug that turns a gushing crack into a dry patch in about a minute — just powder, water and a firm thumb.
What is it?
A single-component, polymer-modified grey powder kneaded into a stiff ball with plain water and pressed straight into a leaking crack or joint. It sets hydraulically, stone-hard, in roughly 60-90 seconds — even while water is actively pushing against it.
Where is it used?
Basements, lift pits, sumps, water tanks, tunnel and shaft linings, retaining walls and masonry — anywhere a running or pressurised leak must be shut off before a coating, membrane or injection system can go in.
Why use it?
Coatings and membranes need a controlled, non-flowing substrate to bond. MC-Fast ST buys that dry window in under two minutes, sets without shrinking so the plug doesn’t pop back out, carries no chlorides that could corrode nearby rebar, and doesn’t mind being applied cold.
How is it applied?
Chisel the leak into a dovetail-shaped key so the plug locks mechanically against reverse water pressure, clear dust and loose material, hand-mix a small batch with roughly 25% water into a thixotropic ball, then press and hold it into the key — starting at the top of a large leak and working downward — until it sets.
About MC-Bauchemie MC-Fast ST
MC-Fast ST (sold in India for years under its earlier name, MC-Fix ST) is MC-Bauchemie’s answer to a leak that won’t wait. It’s a mineral, polymer-modified powder that sets hydraulically the moment it meets water — no catalyst, no two-part mixing, no clock-watching while water keeps finding a way out. Because the reaction is fast and shrinkage-free, the plug locks into a chiselled dovetail key instead of being pushed back out by hydrostatic pressure — the failure mode that makes ordinary patch mortars useless against active seepage.
On Indian sites this earns its keep during monsoon dewatering of basements and lift pits, in occupied buildings where a tank or shaft leak can’t wait for a full waterproofing shutdown, and on tunnelling jobs where a segment joint needs an instant stop-gap. Space Arc supplies and applies MC-Fast ST across Delhi NCR and pan-India as the first step in a proper MC-Bauchemie waterproofing sequence — plug the active leak, then follow through with the right membrane, coating or injection system for a permanent repair.
The technical insight
The chemistry is a fast-hydrating cementitious binder with polymer modification for cohesion — the powder hydrates aggressively on contact with water, generating stone-hard strength within about a minute rather than the hours a normal repair mortar takes. That speed is the entire value proposition, and also its limit: MC-Fast ST is chloride-free, so it won’t accelerate corrosion the way old calcium-chloride “quick-set” cements can, and it isn’t frost-sensitive once cured — but it isn’t a structural repair mortar and was never meant to carry load or replace spalled concrete. Treat it as an emergency plug for water, not a substitute for a proper repair-mortar system.
Where it is used
- Plugging active water leaks and seepage in basements, cellars and retaining walls
- Sealing running leaks in lift pits, sumps and underground water tanks
- Stopping seepage at construction joints and pipe penetrations below grade
- Emergency sealing of leaks in tunnel linings, shafts and segment joints
- Plugging leaks in masonry walls and water towers needing a dry surface
- Pre-treatment ahead of Roofex or other membrane/coating waterproofing systems
- Quick-stop repair for leaking utility pipe penetrations through slabs and walls
- Temporary water cut-off during monsoon dewatering of occupied basements
Key advantages
- Sets stone-hard in 60-90 seconds, even against actively flowing water
- Single-component, ready-to-use — only water needed, no special tools
- Sets hydraulically without shrinkage, so the plug stays locked in the key
- Chloride-free and does not saponify over time, so it’s safe near rebar
- Not sensitive to frost once cured, unlike many quick-set patch compounds
- Works in both horizontal and vertical applications
- Simple hand-mixed application — no pump or injection equipment required
- Buys the dry window needed for a permanent waterproofing treatment
Limitations & considerations
- Extremely short 60-90 second pot life allows only small batches at a time
- It’s a leak-stopping plug, not a structural repair mortar for load-bearing work
- A proper dovetail key is needed for real mechanical lock — surface prep matters
- Finished appearance is rough grey; it’s not meant as a cosmetic repair
- Modest 6-month shelf life; must be stored dry, away from sun, heat and frost
- Addresses the symptom only — a permanent waterproofing system must still follow
Selection & best practice
Mix only what can be placed in one go — larger batches start setting before you can press them home. Chisel a proper dovetail key rather than a straight hole so the cured plug locks mechanically against reverse pressure. On multiple seepage points, work top-down so sealing a lower point doesn’t redirect pressure upward. Below +8°C, use warm water for a predictable set. Never add water to a batch that’s already stiffening — discard and mix fresh. And don’t stop at the plug: schedule the follow-on waterproofing so the structure gets a durable, engineered fix.
Specifications
| Type of product | Ready-to-use, single-component quick-setting plug for leakages |
| Form / colour | Grey powder |
| Pot life / setting time | 60-90 seconds (hardens on mixing at 30°C) |
| Mixing ratio | Approx. 25% water by weight, or as required for consistency |
| Chloride content | Chloride-free |
| Application | Suitable for horizontal and vertical application |
| Shelf life | 6 months from date of manufacture, in unopened packaging |
| Pack size | 30 kg sacks |
| Storage | Unopened packaging, protected from rain, sun, heat and frost |
Industry use cases
Residential/commercial builders
Basement & lift pit dewatering — plugging active seepage points in a below-grade lift pit so it can be pumped dry and handed over for waterproofing.
Facility/plant maintenance
Underground water tank leak repair — stopping a pressurised leak at a tank wall joint during a shutdown, ahead of a permanent tanking system.
Infrastructure/metro contractors
Tunnel and shaft segment joints — emergency plugging of seepage at segment joints during lining works, buying time for injection grouting.
Facility managers, Delhi NCR
Monsoon emergency leak stop — quick plugging of active seepage in occupied basements when a full waterproofing shutdown isn’t possible.
Waterproofing applicators
Pre-treatment before membranes — sealing active wet spots so a membrane or coating can bond to a dry substrate instead of failing over a live leak.
Frequently asked questions
How fast does MC-Fast ST actually set once mixed?
Can it be used against flowing or pressurised water, not just damp seepage?
Is it a permanent repair, or do we still need a waterproofing system afterward?
What pack size does it come in, and how much does one bag cover?
Is it safe near steel reinforcement — won’t a “quick-set” cement corrode rebar?
What’s the difference between MC-Fast ST and an MC-Injekt resin injection?
How we position MC-Bauchemie MC-Fast ST
MC-Fast ST is the first-response product in MC-Bauchemie’s waterproofing range, not a stand-alone system. Space Arc typically pairs it with MC-Injekt acrylic or PU injection resins for a permanent seal once flow stops, with Roofex membranes or Emcephobe coatings for the follow-on waterproofing layer, and with the Nafufill or Emcefix repair-mortar ranges where the surrounding concrete itself needs restoration. Where a specifier wants a broadly equivalent instant plug from another major brand, Fosroc’s Renderoc Plug covers the same emergency-stop niche — a single-component, chloride-free plugging mortar for pressurised leaks — and is a fair alternative to shortlist, particularly on projects already standardised on Fosroc’s Renderoc repair range.
Fosroc Renderoc Plug — A specifier already standardised on Fosroc’s Renderoc repair range, or simply needing an equally fast single-component, chloride-free plugging mortar for a pressurised leak, would reasonably shortlist Renderoc Plug alongside MC-Fast ST.
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