STP ShaliPlast HP
STP’s chloride-free naphthalene sulphonate superplasticizer — IS 9103 and ASTM C494 Type A & F compliant — for high-strength, pumpable, dense concrete at 0.4–2.0% dosage.
What is it?
A high-range water-reducing admixture (superplasticizer) from STP Ltd, built on a modified naphthalene sulphonate polymer. Known to older specifications as ShaliCon 37, it is chloride-free and conforms to IS 9103 and ASTM C494 Type A & F.
Where is it used?
Ready-mix and site-batched concrete: heavily reinforced RCC, pumped and flowing mixes, high-performance structural grades, prestressed and precast elements, and dense waterproofed concrete for basements and tanks.
Why use it?
It buys workability without extra water, so you get a lower water-cement ratio, higher early and ultimate strength, a denser and less permeable matrix, and easier placement — with nil chloride, safe for tendons and rebar.
How is it applied?
Dosed at 0.4–2.0% by weight of cement into the final mixing water — never onto dry cement — at the batching plant or at site, with the optimum dose fixed by trial mixes.
About STP ShaliPlast HP
ShaliPlast HP is STP Ltd’s high-range water-reducing admixture, formulated on a modified naphthalene sulphonate polymer and sold in earlier years as ShaliCon 37. It conforms to IS 9103 and qualifies under ASTM C494 as both a Type A water reducer and a Type F high-range water reducer, arriving as an amber-brown liquid that can be dosed at the ready-mix plant or straight into the site mixer. Space Arc Engineering supplies it in 20 kg and 200 kg drums to RMC producers, contractors and precasters across Delhi NCR, with Pan-India dispatch and TDS support.
The admixture earns its place wherever a mix needs more workability than its water-cement ratio would normally permit. Dosed between 0.4 and 2.0 per cent by weight of cement, it typically trims mixing water by 15 to 25 per cent — enough to push site-practical mixes through the M30–M70 band without piling on cement. Because the formulation carries nil chloride, it is cleared for prestressed and heavily reinforced work where corrosion of tendons is the governing concern, and it runs happily with every Portland cement in Indian supply, sulphate-resisting cement included. High-alumina cement is the one hard exclusion.
The technical insight
Naphthalene sulphonate superplasticizers work by electrostatics. In a plain mix, cement grains clump into flocs that trap a share of the mixing water, and that trapped water contributes nothing to fluidity. ShaliPlast HP’s sulphonate groups adsorb onto the grain surfaces and give every particle the same negative charge; the grains repel one another, the flocs break apart, and the freed water lubricates the mix. That is why slump jumps sharply at constant water — or why you can cut water while holding slump, dropping the water-cement ratio and densifying the hardened paste, which is where the strength, impermeability and surface-finish gains come from. The same adsorption chemistry explains STP’s overdose warning: beyond the recommended range the cement grains stay dispersed too long and setting is retarded severely, so trial mixes are not optional.
Where it is used
- Ready-mix concrete, dosed at the plant or at site
- High-performance and high-strength structural concrete
- Flowing, high-slump concrete for congested reinforcement
- Pumped concrete for high-rise pours and long pipeline runs
- Prestressed and precast elements where chloride is barred
- Self-compacting concrete mixes
- Dense waterproofed concrete for basements and water-retaining structures
Key advantages
- High-range water reduction — typically 15–25% — at practical dosages
- Remarkable gains in both early and ultimate compressive strength
- Major workability improvement with no added water and no segregation risk
- Denser, less permeable concrete with a cleaner surface finish
- Nil chloride content — safe for prestressing tendons and reinforcement
- Easier placement and compaction, cutting labour cost on the pour
- Compatible with all Portland cements, including sulphate-resisting cement
Limitations & considerations
- Overdosing extends setting time severely — stay inside the 0.4–2.0% window and verify by trial
- Slump retention is shorter than PCE admixtures; long hot-weather hauls call for a retarder or a PCE switch
- Not compatible with high-alumina cement
- Must be dosed separately from other admixtures and must never contact dry cement
- Air-entrainer dosage has to be cut when used together, as HP raises its air-generating efficiency
- Nine-month shelf life — plan drum stocks around consumption, stored cool and under shed
Selection & best practice
Add ShaliPlast HP to the final dosing water only — it must never touch dry cement. STP’s batching sequence is specific: charge the concrete materials into the mixer in the proper order with about 70 per cent of the mixing water and mix for three minutes, then add the remaining water carrying the admixture and mix for three minutes more before checking slump. Establish the dose by trial between 0.4 and 2.0 per cent by weight of cement, starting low, since the set retardation required shifts the optimum. Where the design includes other admixtures — waterproofers, retarders, air-entrainers — dose each one into the mix separately, never pre-blended, and recalibrate any air-entraining agent downward. Store drums cool and dry under shed, away from heat, and consume within nine months of manufacture.
Specifications
| Chemical base | Modified naphthalene sulphonate polymer |
| Standards compliance | IS 9103; ASTM C494 Type A & F |
| Form / colour | Amber-brown liquid |
| Chloride content | Nil |
| pH | 7–8 |
| Dosage | 0.4–2.0% by weight of cement (optimum fixed by site trial) |
| Packing | 20 kg and 200 kg drums |
| Shelf life | 9 months in original unopened packing |
| Storage | Cool, dry, under shed, away from heat |
Industry use cases
Ready-Mix Concrete Plants
Plant-dosed into transit mixers for pumpable commercial grades; producers running long lead times pair it with ShaliPlast R retarder to stretch the naphthalene slump window.
High-Rise & Commercial RCC
Columns, core walls and congested rafts take flowing concrete that moves around dense steel and compacts fully without a drop of extra water.
Precast & Prestressed Yards
Nil-chloride chemistry protects tendons while the early-strength gain speeds up mould and casting-bed turnover.
Bridges & Infrastructure
Heavily reinforced pier caps, girders and pump-placed deck pours benefit from the low water-cement ratio at full workability.
Basements & Water-Retaining Structures
The denser, less permeable matrix supports waterproofed-concrete designs for rafts, tanks and below-grade walls.
Frequently asked questions
What is the dosage of ShaliPlast HP?
What happens if it is overdosed?
Is it safe for prestressed concrete?
How does it compare with a PCE superplasticizer?
Which cements is it compatible with?
What pack sizes are available and what is the shelf life?
How we position STP ShaliPlast HP
Within the STP admixture family, ShaliPlast HP is the workhorse naphthalene option. Specifiers chasing longer slump retention, steeper water reduction or self-compacting mixes should step up to the ShaliPlast PCE 300-series polycarboxylates, while RMC producers with long transit times commonly pair HP with ShaliPlast R retarder. Space Arc also stocks the matching chemistry from Fosroc — Conplast SP430 — alongside Fosroc’s Auramix PCE range, so consultants can hold a single supplier while honouring whichever admixture brand the project specification names.
Fosroc Conplast SP430 — The like-for-like naphthalene sulphonate superplasticizer specifiers choose when the project is already standardised on Fosroc admixtures or needs Fosroc’s grade variants and RMC dosing support.
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