STP ShaliPlast Shotcrete P
Chloride-free powder set accelerator for dry-process shotcrete — 3–4 minute initial set, lower rebound and confident overhead guniting in tunnels, slopes and marine structures.
What is it?
A ready-to-use, chloride-free inorganic powder admixture from STP Limited (formerly ShaliSR-SC P) that flash-accelerates setting in dry-process shotcrete and gunite, conforming to ASTM C-1141 Type II Grade I Class B.
Where is it used?
Tunnel and mining linings, cut-slope guniting, dams, retaining walls, manholes, bridge structures, parking decks, and piers or dock supports in marine environments.
Why use it?
It pulls initial set down to 3–4 minutes so sprayed layers grip overhead and vertical faces with low rebound, adds water-tightness, and does it all without chlorides that attack reinforcement.
How is it applied?
Metered into the dry gunite mix at 3–8% by weight of cement and charged at the gun near the nozzle tip; the working dose is fixed through site trials with the project cement.
About STP ShaliPlast Shotcrete P
ShaliPlast Shotcrete P is STP Limited’s powder set-accelerating and shotcreting admixture, built for dry-process gunite where the mix must stiffen the instant it strikes the receiving face. The chloride-free inorganic powder brings initial set down to 3–4 minutes and final set to 10–12 minutes at 27°C, so freshly sprayed concrete holds on vertical rock, damp substrates and overhead tunnel crowns instead of sloughing away. Because the acceleration comes without chlorides, it can be sprayed over rebar, mesh and rock bolts without setting up the corrosion cell that older calcium-chloride accelerators were notorious for. The product conforms to ASTM C-1141 Type II Grade I Class B and doubles as a water-tightness aid, reducing the permeability of the finished layer.
Space Arc Engineering supplies ShaliPlast Shotcrete P in 20 kg bags across Delhi NCR and pan-India, with applicator-grade support behind it. Shotcrete accelerators are dose-sensitive — cement brand, content and ambient conditions all shift the setting response — so our team helps contractors run the site trials that fix the working dosage within the 3–8% band before production spraying begins. For tunnel, hydro and slope packages we also coordinate supply schedules so a hygroscopic product never sits exposed at site.
The technical insight
The mechanism is deliberate interference with cement hydration kinetics. ShaliPlast Shotcrete P is an alkaline inorganic powder (pH 10–11) that dissolves into the mixing water at the nozzle and sharply speeds the early reactions of the cement’s aluminate and silicate phases. Hydration products begin bridging between particles within minutes rather than hours, so the paste loses mobility almost on impact — that is what lets a nozzleman build thickness overhead, and why rebound drops: material that stiffens on contact stays on the face instead of bouncing off. The same dense, rapidly formed hydrate structure closes capillary pathways, which is where the improved water-tightness and low-shrinkage behaviour come from. Being hygroscopic, the powder is reactive by nature — which is also why bag discipline on site matters.
Where it is used
- Initial and secondary shotcrete support in tunnels and mining excavations
- Guniting of cut slopes and embankments with mesh and soil nails
- Repair and re-profiling of retaining walls and manholes
- Dams, spillways and hydraulic structures needing water-tight sprayed linings
- Piers and dock supports in marine environments
- Bridge structures and parking decks restored by dry-process gunite
- General guniting projects over damp or wet substrates
Key advantages
- Initial set in 3–4 minutes lets sprayed layers hold on overhead and vertical faces
- Low rebound — more material stays on the face, less swept off the invert
- Nil chloride content protects rebar, mesh and rock bolts from corrosion
- Improves water-tightness and cuts permeability of the finished layer
- Low-shrinkage behaviour in the accelerated matrix
- Sprays onto damp or wet surfaces with no bond coat required
- Ready-to-use powder that meters easily at the gun
- Eco-friendly formulation per the manufacturer
Limitations & considerations
- Formulated for dry-process gunite — wet-mix crews should specify the liquid grade (ShaliPlast Shotcrete L) instead
- Hygroscopic: an opened or poorly stored bag absorbs moisture and loses performance, so monsoon storage discipline is essential
- Setting response shifts with cement brand, quality and content — site trials are mandatory before fixing the production dose
- As with any flash-set accelerator, pushing toward the top of the dosage band can trade away ultimate strength; verify with test panels or cores
- Shelf life is a relatively short 9 months in unopened original packing
- Stated performance is at 27°C / 55% RH — hot or cold extremes call for ACI weather-concreting practice and material conditioned to 18–29°C
Selection & best practice
Start with the substrate: the face to be shotcreted must be clean, sound and rough. Remove oil, paint, debris and unsound concrete, then mechanically prepare with a bush hammer, sandblaster or jackhammer to at least a 3 mm profile that exposes coarse aggregate, and finish by vacuuming or pressure-washing all residue. No bond coat is needed. Set up the guniting equipment close to the placement area and charge ShaliPlast Shotcrete P directly at the gun near the nozzle tip, keeping the dose within 3–8% by weight of cement — a band that supports layer thicknesses up to about 15 cm in one pass, with a minimum applied thickness of 1.3 mm. Skilled nozzle operation and thorough mixing are non-negotiable; adjust mix workability to the equipment, its capacity and site temperature. Condition material to 18–29°C for optimum results, keep bags sealed and dry, and wash tools with water before the material hardens. The powder is alkaline, so wear gloves, eye protection and avoid inhaling dust.
Specifications
| Form / colour | White powder (inorganic substance) |
| Initial setting time (27°C, 55% RH) | 3–4 minutes |
| Final setting time (27°C, 55% RH) | 10–12 minutes |
| Chloride content | Nil |
| pH | 10–11 |
| Dosage | 3–8% by weight of cement (layer up to ~15 cm per pass; fix by site trials) |
| Standard compliance | ASTM C-1141 Type II Grade I Class B |
| Packing | 20 kg bag |
| Shelf life | 9 months in original unopened packing, stored cool and dry |
Industry use cases
Tunnels & Hydropower
Rapid-set support shotcrete on damp rock in NATM headings, adits and shafts, where a 3–4 minute set keeps crown layers in place and cycles moving.
Highways & Slope Stabilization
Guniting cut slopes and embankments over mesh and soil nails on expressway and hill-road packages, with low rebound keeping material on steep faces.
Marine & Ports
Sprayed repair of piers and dock supports, where nil chloride content matters most for reinforcement already fighting a saline exposure.
Dams & Irrigation
Water-tight sprayed linings and re-profiling on spillways and hydraulic structures, exploiting the reduced-permeability matrix.
Urban Repair & Rehabilitation
Gunite restoration of retaining walls, manholes, parking decks and bridge members where overhead and vertical build-up is unavoidable.
Frequently asked questions
What is the dosage of ShaliPlast Shotcrete P?
Is it for dry-mix or wet-mix shotcrete?
Will it corrode reinforcement or rock bolts?
How fast does it actually set?
How should it be stored on site, especially in monsoon?
Which standard does it comply with?
How we position STP ShaliPlast Shotcrete P
Within the STP family, ShaliPlast Shotcrete P is the dry-process half of a pair: wet-mix crews should move to ShaliPlast Shotcrete L, its liquid set-accelerating counterpart. For the base concrete itself, ShaliPlast PCE-series superplasticizers handle water reduction and pumpability, while ShaliPlast CI adds a corrosion inhibitor where marine exposure is severe. Where the wider scope runs into structural repair behind the sprayed layer, STP’s RestoFix repair range and Fosroc’s Renderoc systems both sit in our catalogue. And when the job needs chloride-free set acceleration for poured or precast concrete rather than sprayed gunite, Fosroc Conplast NC is the honest fit — talk to Space Arc and we will match the accelerator to the placement method, not the other way around.
Fosroc Conplast NC — Specify Conplast NC when the need is chloride-free set acceleration for poured, precast or cold-weather concrete placed conventionally — it is a liquid admixture for cast concrete, while Shotcrete P remains the pick for dry-process sprayed work.
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