STP ShaliPlast Shotcrete L
Silicate-based, chloride-free liquid accelerator dosed at the shotcrete nozzle — initial set in 3-4 minutes, low rebound, overhead spraying on damp surfaces. Conforms to ASTM C1141 Type II, Grade I, Class A.
What is it?
A silicate-based, chloride-free liquid set accelerator from STP Limited (formerly Shali SR-SC (SL)), metered in at the nozzle so sprayed concrete stiffens within minutes of hitting the surface.
Where is it used?
Tunnel linings, guniting and slope-stabilisation work, marine piers and dock supports, dams, retaining walls, parking decks, bridge structures and manhole rehabilitation.
Why use it?
Initial set in 3-4 minutes with noticeably lower rebound, so concrete grips overhead and damp faces instead of falling back — and nil chloride content means no corrosion risk to embedded rebar.
How is it applied?
Added directly to the shotcrete gun near the nozzle tip at 3-12% by weight of cement; the working dose is fixed through site trials, for layer thicknesses up to about 20 cm in a single pass.
About STP ShaliPlast Shotcrete L
ShaliPlast Shotcrete L is STP Limited’s liquid set-accelerating and shotcreting admixture, built on silicate chemistry and completely free of chlorides. Injected at the nozzle of wet-mix spraying equipment, it collapses the setting time of the cement paste to 3-4 minutes initial and 10-12 minutes final, which is what lets a nozzleman build thickness overhead or on a wet rock face without the material sloughing off. Alongside acceleration it improves the watertightness of the placed layer, and it carries compliance with ASTM C1141 Type II, Grade I, Class A.
Space Arc Engineering supplies ShaliPlast Shotcrete L across Delhi NCR and Pan-India in 20 kg and 200 kg drums, backed by application crews who have handled guniting and sprayed-concrete work on slopes, linings and repair jobs. Because dose response shifts with every cement source, we help contractors run the site trials that convert the 3-12% dosage window into one dependable number for their mix.
The technical insight
The active silicate reacts almost instantly with the calcium hydroxide and calcium ions released by hydrating cement, precipitating a calcium silicate hydrate gel throughout the fresh paste. That gel bridges the cement grains and flash-stiffens the sprayed layer, which is why rebound drops — material that arrives sticks, rather than bouncing off partially stiffened concrete. The same reaction densifies the pore structure, cutting permeability and improving watertightness, and it is why early strengths climb past 5 MPa within 8 hours and 14 MPa in a day. The reaction is strongly dose- and cement-sensitive: alkali content, C3A levels and cement quantity all shift the response, which is exactly why the TDS insists on site trials rather than a fixed dose.
Where it is used
- Tunnel and underground cavern linings where each sprayed pass must self-support within minutes
- Slope stabilisation and rock-face guniting on hill roads, rail cuttings and landslide-prone stretches
- Marine environments — piers, dock supports and structures under splash or tidal exposure
- Dams, spillways and hydraulic structures where reduced permeability matters as much as speed
- Retaining walls and reinforced-earth structures repaired or faced by sprayed concrete
- Parking decks and bridge structures needing overhead soffit repair without formwork
- Manhole and sewer-shaft rehabilitation by wet-spray application
- General guniting projects on damp or irregular substrates
Key advantages
- Initial set in 3-4 minutes and final set in 10-12 minutes, so build-up is fast even overhead
- Early strength above 5 MPa at 8 hours and 14 MPa at 1 day, allowing quick advance to the next cycle
- Low rebound — less material bouncing off the face means real savings on wasted concrete
- Enables spraying onto wet surfaces and overhead faces where plain shotcrete would slump
- Nil chloride content, so it adds no corrosion risk to rebar or embedded steel
- Improved watertightness and reduced permeability of the finished layer
- Low shrinkage behaviour in the accelerated matrix
- No bond coat required on a properly prepared substrate
Limitations & considerations
- The 3-12% dosage window is wide, and set response swings with cement brand, cement content and temperature — site trials are mandatory, not a formality
- Alkaline silicate chemistry (pH 10-11) demands full PPE at the nozzle; projects that specify alkali-free accelerators need a different chemistry altogether
- As with silicate accelerators generally, pushing the dose high can trade away long-term strength — hold to the minimum dose the trial supports
- It is a liquid designed for wet-mix nozzle dosing; for dry-mix guniting, STP’s powder grade ShaliPlast Shotcrete P is the correct selection
- Shelf life is 9 months unopened, and the material should be conditioned to 18-29 deg C before use — plan tunnel stockyard procurement accordingly
Selection & best practice
Get the substrate right first: the receiving concrete must be clean, sound and mechanically roughened — bush hammer, sandblast or jackhammer to a minimum 3 mm profile that exposes coarse aggregate — then vacuum or pressure-wash away every trace of residue. No bond coat is needed. Set up the wet-spray rig close to the placement area and meter ShaliPlast Shotcrete L into the gun near the nozzle tip; thorough mixing within the stream and a skilled nozzleman decide the quality of the finished layer. Adjust the base-mix workability to suit the pump, ambient temperature and spray distance, follow ACI hot- and cold-weather concreting practice in adverse conditions, respect the 1.3 mm minimum applied thickness, and wash tools and lines with water before the material hardens.
Specifications
| Form / colour | Colourless liquid |
| Specific gravity | 1.30 – 1.40 |
| pH | 10 – 11 |
| Chloride content | Nil |
| Setting time | Initial 3-4 min; final 10-12 min |
| Typical compressive strength | >5 MPa at 8 h; >14 MPa at 1 day; >23 MPa at 3 days |
| Dosage | 3-12% by weight of cement (finalised by site trials); layers up to ~20 cm per pass |
| Standards compliance | ASTM C1141 Type II, Grade I, Class A |
| Packing / shelf life | 20 kg and 200 kg drums; 9 months unopened |
Industry use cases
Tunnels & Metro
NATM headings, primary linings and cavern support where every sprayed pass has to carry its own weight within minutes so the cycle can advance.
Hill Roads & Railways
Guniting of cut slopes and unstable faces along Himalayan highways and rail corridors, where crews spray onto damp, irregular rock.
Marine & Hydro
Piers, dock supports, dams and spillway repairs where the silicate’s reduced permeability adds watertightness on top of fast set.
Municipal Rehabilitation
Manholes, sewer shafts and retaining walls re-lined by overhead wet-spray without the cost and delay of formwork.
Bridges & Parking Structures
Deck soffit and pier repairs placed overhead in short possessions, with 8-hour strengths above 5 MPa supporting quick reopening.
Frequently asked questions
What dosage should we start trials at?
Is it safe to use over reinforced sections?
Is this for wet-mix or dry-mix shotcrete?
How fast does it set and gain strength?
What pack sizes are available and how should it be stored?
Does it also act as a waterproofer?
How we position STP ShaliPlast Shotcrete L
Within the STP family, ShaliPlast Shotcrete L is the wet-mix half of a pair — specify ShaliPlast Shotcrete P where the job runs dry-mix guniting equipment, and draw the base mix’s water reduction and pumpability from STP’s wider ShaliPlast admixture range rather than leaning on the accelerator to fix workability. Where acceleration is needed in form-cast or pumped concrete rather than at a spray nozzle, Fosroc Conplast NC from our Fosroc line is the cleaner fit as a mixer-added, chloride-free accelerator. Space Arc supplies all of these Pan-India with dosage-trial support from one desk.
Fosroc Conplast NC — Specifiers choose Conplast NC when the accelerated set is needed in conventionally placed or cold-weather concrete added at the mixer, rather than a silicate dosed at the shotcrete nozzle.
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