Fosroc Conplast RP
Chloride-free, lignosulphonate-based water-reducing and set-retarding admixture (IS 9103 / ASTM C494 Type D) – supplied by Space Arc Engineering, authorised Fosroc distributor and applicator across Delhi NCR and Pan-India.
What is it?
Fosroc Conplast RP is the ‘Retarding Plasticiser’ family of chloride-free, water-reducing and set-retarding concrete admixtures based on selected lignosulphonate materials, classified to IS 9103:1999 and ASTM C494 Type D. It is sold under numbered catalogue references (RP200, RP250, RP264, RP2020, RP2100) rather than as a single un-numbered ‘Conplast RP’.
Where is it used?
Used in ready-mix and site-batched structural concrete where both water reduction and controlled delay of setting are required – mass pours, hot-weather concreting, and concrete that must remain workable during placement.
Why use it?
Reduces water demand to improve compressive strength and durability while extending the working/stiffening time of the mix, helping avoid cold joints and improving finishability without adding chlorides.
How is it applied?
Dispersed into the concrete via the gauging water and dosed in litres per 100 kg of cementitious material (RP264 reference: 0.2-0.6 L/100 kg), not as a percentage by weight of cement. Trial mixes with project materials confirm the optimum dosage.
About Fosroc Conplast RP
Fosroc Conplast RP is a family of chloride-free, water-reducing and set-retarding concrete admixtures, where “RP” stands for Retarding Plasticiser. It is based on selected lignosulphonate materials and is supplied as a brown solution that instantly disperses in water. The range is classified to IS 9103:1999 and ASTM C494 as a Type D admixture, meaning it combines water reduction with controlled retardation of set in a single product.
A common error on product pages is to present the range as a generic, un-numbered “Conplast RP”. Fosroc does not market a single product by that bare name – the actual catalogue references are numbered: Conplast RP200, RP250, RP264, RP2020 and RP2100. Each numbered variant has its own official Technical Data Sheet (TDS) with its specific dosage envelope and properties, so the correct variant should always be confirmed against the relevant TDS for a given mix design and project specification.
The chemistry is equally important to state correctly. The Conplast RP family is built on a lignosulphonate base – it is not simply a “combined retarding and plasticizing” Type D product with no named base. The lignosulphonate chemistry is what delivers simultaneous water reduction and set retardation, and Fosroc explicitly describes the product as a chloride-free admixture (less than 0.05% chloride by weight), which makes it suitable for use in reinforced and prestressed concrete where chloride ingress must be controlled.
Space Arc Engineering supplies Fosroc Conplast RP as an authorised Fosroc distributor and applicator serving Delhi NCR and Pan-India, with technical support for variant selection, trial-mix dosage optimisation, and supply alongside the wider Fosroc admixture and construction-chemicals portfolio.
The technical insight
The defining technical point is the dosing basis. Conplast RP is a liquid admixture dosed in LITRES per 100 kg of cementitious material – for the RP264 reference, typically 0.2-0.6 L/100 kg (usual range 0.25-0.6 L/100 kg) – and NOT as a percentage by weight of cement, which is the wrong unit basis for a liquid product of this type. With a specific gravity of 1.170-1.190 at 30 degrees C (RP264 reference), the admixture is added through the gauging water, into which it instantly disperses. Because it is chloride-free (less than 0.05% chloride by weight) and entrains less than 2% additional air at normal dosage, it does not introduce the durability risks associated with chloride-bearing or heavily air-entraining admixtures. The lignosulphonate base drives both functions: water is reduced to lift compressive strength and durability at a given workability, while set is retarded in a controlled way to extend the working and stiffening window. Optimum dosage is always confirmed by trial mixes using the actual project cement and aggregates, since cement chemistry and ambient temperature influence both the water reduction achieved and the degree of retardation.
Where it is used
- Structural concrete requiring simultaneous water reduction and controlled set retardation under IS 9103 / ASTM C494 Type D
- Concrete that must remain workable for extended periods during placement to avoid cold joints
- Mass concrete pours where delayed setting helps manage heat of hydration and continuous placement
- Hot-weather concreting where extended working time supports proper placing and finishing
- Reinforced and prestressed concrete where a chloride-free admixture is required
- Ready-mix and site-batched concrete where improved compressive strength and durability are targeted at a given workability
Key advantages
- Chloride-free (less than 0.05% chloride by weight) – suitable for reinforced and prestressed concrete
- Dual action: water reduction plus controlled set retardation in a single Type D admixture
- Lignosulphonate base instantly disperses in the gauging water for uniform distribution
- Improves compressive strength and durability through reduced water demand at equal workability
- Extends working and stiffening time to help avoid cold joints and ease placement
- Low air entrainment – less than 2% additional air at normal dosage
- Conforms to IS 9103:1999 and ASTM C494 Type D
Limitations & considerations
- Sold only as numbered variants (RP200, RP250, RP264, RP2020, RP2100) – the correct SKU and its own TDS must be confirmed for each application
- Dosage must be measured in litres per 100 kg of cementitious material, not as a percentage by weight of cement
- Degree of retardation and water reduction varies with cement chemistry and ambient temperature, so trial mixes are essential
- As a retarder, it delays set – overdosing or use in cold conditions can extend setting times beyond what is intended
- Performance figures should be taken from the specific variant’s official Fosroc TDS rather than assumed from the family name
Selection & best practice
Always select and specify the exact numbered variant (e.g. Conplast RP264) against its current Fosroc Technical Data Sheet, and dose in litres per 100 kg of cementitious material. Confirm the optimum dosage within the variant’s stated range through trial mixes using the actual project cement, aggregates and expected ambient temperature, since both water reduction and the degree of set retardation depend on these. Add the admixture via the gauging water for instant dispersion, and verify the chloride-free status and Type D classification against the TDS where the specification requires it.
Specifications
| Chemical base | Selected lignosulphonate materials (chloride-free water-reducing & retarding admixture) |
| Appearance | Brown solution/liquid that instantly disperses in water |
| Specific gravity | 1.170 – 1.190 at 30°C (Conplast RP264 reference) |
| Typical dosage | 0.2-0.6 litres per 100 kg of cementitious material (RP264; usual range 0.25-0.6 L/100 kg) – dosed in litres per 100 kg, not % by weight |
| Chloride content | Chloride free; less than 0.05% by weight |
| Standards | IS 9103:1999 and ASTM C494 Type D |
| Air entrainment | Less than 2% additional air entrained at normal dosage |
| Primary use | Water reduction to improve compressive strength/durability plus controlled retardation to extend working/stiffening time |
Industry use cases
Ready-Mix Concrete (RMC)
Batched into RMC to reduce water demand for higher strength and durability while retarding set, supporting workability through dispatch and placement. Dosed in litres per 100 kg of cementitious material per the relevant RP variant TDS.
Mass & Foundation Concrete
Controlled retardation helps manage continuous large pours and heat of hydration in rafts, footings and mass elements, reducing the risk of cold joints between layers.
Hot-Weather Concreting
Extends the working and stiffening window so concrete can be placed and finished correctly in elevated ambient temperatures, with the exact dosage confirmed by trial mix for site conditions.
Reinforced & Prestressed Structures
Its chloride-free chemistry (less than 0.05% chloride by weight) makes it appropriate where chloride ingress to reinforcement or tendons must be avoided, while still delivering Type D water reduction and retardation.
Frequently asked questions
Is ‘Conplast RP’ a single product?
How is Conplast RP dosed?
What is the chemical base of Conplast RP?
Is Conplast RP chloride-free?
Which standards does it meet?
Does it entrain air?
Where can I buy Fosroc Conplast RP in India?
How we position Fosroc Conplast RP
Positioned as a chloride-free, lignosulphonate-based Type D (IS 9103 / ASTM C494) water-reducing and set-retarding admixture, supplied through Space Arc Engineering as an authorised Fosroc distributor and applicator. It sits in the retarding-plasticiser segment alongside Fosroc’s own range and credible alternative brands such as BASF/Master Builders Solutions (MasterPozzolith / Pozzolith), Sika (SikaPlast / Plastiment retarding ranges) and Chryso. The Fosroc Conplast RP family is named first and specified by its exact numbered variant (RP200/RP250/RP264/RP2020/RP2100), with dosage stated correctly in litres per 100 kg of cementitious material.
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