STP ShaliPlast R
Chloride-free set retarding admixture from STP Limited that keeps concrete workable through long hauls, hot afternoons and large continuous pours — compliant with IS 9103 and ASTM C494 Type B.
What is it?
A liquid set-retarding admixture for concrete from STP Limited, formerly sold as ShaliCon Retarder. It slows the initial set so the mix stays plastic and placeable for longer.
Where is it used?
Ready-mixed concrete on long transit routes, mass and structural concrete, bridge decks, highway pavements, lightweight concrete and any pour going down in hot weather.
Why use it?
It holds slump at high concrete temperatures, prevents cold joints between successive lifts and contains nil chlorides — so it is safe around reinforcement and prestressing steel.
How is it applied?
Dosed at 0.2–1.5% by weight of cement into the mixing water at the batching plant or site mixer. It must never contact dry cement, and the working dose is fixed by trial mixes.
About STP ShaliPlast R
ShaliPlast R is a set-retarding admixture manufactured by STP Limited, the Delhi-headquartered construction chemicals company with over eight decades in waterproofing, admixtures and repair systems. Supplied as an amber-brown liquid and formerly marketed as ShaliCon Retarder, it conforms to IS 9103 and ASTM C494 Type B. Added at 0.2 to 1.5 percent by weight of cement, it extends the period during which fresh concrete remains workable, and STP credits it with secondary gains in durability through reduced shrinkage and permeability in the hardened concrete.
For Indian site conditions the case for a retarder is straightforward. Concrete batched at 35 degrees loses slump quickly, and a transit mixer held up in NCR traffic can arrive with a mix that is already stiffening. Mass rafts must stay monolithic across pour fronts, and bridge decks are often designed to be stressed across the full section before initial set occurs. ShaliPlast R gives the site engineer predictable control over setting in all of these situations without introducing chlorides into the mix. Space Arc Engineering stocks it in 20 kg and 200 kg containers and supports customers with dosage trials before production batching begins.
The technical insight
Retarders work at the cement-water interface. When ShaliPlast R enters the mix through the gauging water, its molecules adsorb onto cement grains and the first hydration products, forming a temporary barrier that starves the silicate phases of water and stretches the dormant period of hydration. The concrete stays plastic because the stiffening reactions have been postponed, not diluted — once hydration resumes, it proceeds normally, which is why a correctly dosed retarder does not sacrifice the concrete’s design strength. The effect scales with dose across the 0.2–1.5% window, but it also shifts with cement chemistry, fineness, water-cement ratio and ambient temperature. That is why STP’s own data sheet insists on trial mixes: the same dose that buys two useful hours with one OPC in April may behave differently with a blended cement in June. Overdosing is the real hazard — set times extend severely — so calibrated dispensers matter.
Where it is used
- Ready-mixed concrete travelling long distances from batching plant to site
- Hot weather concreting where slump loss would otherwise force retempering
- Mass concrete — rafts, dams and heavy foundations poured in continuous lifts
- Bridge deck concrete where the full section must be stressed before initial set
- Structural concrete in large or congested pours needing extended placing time
- Highway and pavement-quality concrete behind paving trains
- Lightweight concrete requiring extended open time
Key advantages
- Long-lasting control of slump loss even at high concrete temperatures
- Eliminates cold joints between successive pours in mass and structural work
- Chloride content nil — no corrosion risk to rebar or prestressing strand
- Easier handling and finishing of the fresh mix
- Reduces shrinkage and permeability, improving long-term durability
- Makes long-haul transport of ready-mixed concrete practical
- Wide 0.2–1.5% dosage window lets you tune retardation to the pour
Limitations & considerations
- Overdosing extends setting time severely — dispenser calibration and strict batching discipline are non-negotiable
- Retardation achieved varies with cement type, dose, mix design and temperature; there is no fixed figure without site trial mixes
- It is a pure Type B retarder, not a water reducer — where you also need plasticising, a separate compatible admixture must be trialled alongside it
- Must be added to the mixing water only; direct contact with dry cement is not permitted
- Delayed setting pushes back finishing operations and formwork striking, so pour scheduling has to account for it
- Shelf life is 9 months unopened, and containers must be stored cool, dry and under shed away from heat
Selection & best practice
Always introduce ShaliPlast R through the mixing water — never onto dry cement or aggregate. STP’s recommended sequence is to charge the mixer with all concrete materials and roughly 70 percent of the mixing water, mix for three minutes, then add the remaining water carrying the admixture and mix for a further three minutes until the target slump is reached. Before production, run trial mixes with the actual project cement at realistic ambient temperatures to fix the dose within the 0.2–1.5% by weight of cement range for the retardation you need; repeat trials if the cement source or season changes. Use a calibrated dispenser at the batching plant, since the penalty for overdosing is a severely extended set. Keep unopened containers under shed, away from heat, and rotate stock within the 9-month shelf life. The product is non-toxic; wash skin splashes with water and seek medical advice for eye contact.
Specifications
| Form / Colour | Liquid, amber brown |
| Specific gravity | 1.13 – 1.19 |
| pH | 7 – 8 |
| Chloride content | Nil |
| Dosage | 0.2 – 1.5% by weight of cement (fix by trial mix) |
| Standards compliance | IS 9103; ASTM C494 Type B |
| Packing | 20 kg and 200 kg containers |
| Shelf life | 9 months in original unopened condition |
| Storage | Cool, dry, under shed, away from heat |
Industry use cases
Ready-Mix Concrete
RMC plants serving Delhi NCR and other metros use ShaliPlast R to keep mixes placeable through long transit and traffic delays, cutting rejected loads and site retempering.
Bridges & Flyovers
Deck pours designed to be stressed across the entire section before initial set rely on controlled retardation; the nil-chloride formulation suits prestressed construction.
Industrial & Mass Foundations
Turbine rafts, machine foundations and large mats poured in continuous lifts use retarded concrete to keep each lift live until the next arrives, avoiding cold joints.
Highways & Pavements
PQC paving in warm weather benefits from extended open time behind the paver, holding workability without added water.
High-Rise Construction
Summer slab and core pours in hot Indian conditions stay workable through pumping and placing sequences when set control is dosed into the mix at the plant.
Frequently asked questions
What is the dosage of ShaliPlast R?
Will a retarder reduce my concrete’s final strength?
How is ShaliPlast R different from a plasticiser or superplasticiser?
Is it safe for reinforced and prestressed concrete?
How much retardation will I actually get?
What pack sizes does Space Arc supply, and what is the shelf life?
How we position STP ShaliPlast R
ShaliPlast R is the set-control product within STP’s ShaliPlast admixture family. When a pour needs water reduction or higher workability as well as extended open time, pair it after compatibility trials with a ShaliPlast plasticising grade from the same range, and where chloride-induced rebar corrosion is the design concern, STP’s ShaliPlast CI corrosion-inhibiting admixture is the more targeted choice. Projects standardised on Fosroc can achieve equivalent set control with Conplast R, which we also stock. Space Arc Engineering supplies both brands with genuine material, pan-India logistics and dosage-trial support on request.
Fosroc Conplast R — Specify Conplast R when the project’s admixture schedule is already standardised on Fosroc’s Conplast system or the consultant requires single-brand admixture sourcing across the mix design.
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