Fosroc Conplast WP320
Chloride-free dual-action admixture that combines high-range water reduction with integral permeability control for dense, durable, watertight concrete.
What is it?
A chloride-free liquid concrete admixture from Fosroc that works as a superplasticiser and a permeability-reducing agent at the same time, using a formulated blend of dispersants and permeability reducers.
Where is it used?
Water-retaining and water-excluding structures: basements, RC roofs, water tanks, STPs/ETPs, podiums, retaining walls and other high-durability RCC where both strength and low permeability matter.
Why use it?
It lets you cut the water-cement ratio sharply (raising strength) while densifying the matrix to reduce water ingress, so one product covers workability, strength and integral waterproofing.
How is it applied?
Dosed into the gauging/mix water with a calibrated dispenser at the batching plant or mixer; never poured neat onto dry cement. Optimum dosage is confirmed by site trial mixes.
About Fosroc Conplast WP320
Fosroc Conplast WP320 is a chloride-free, superplasticising admixture built around a formulated blend of dispersants and permeability-reducing agents. Supplied as a brown solution that disperses instantly in the mixing water, it sits in Fosroc’s Conplast family of concrete admixtures alongside the SP-series superplasticisers and the WL/WP integral-waterproofing range, but it deliberately bridges the two: it behaves like a high-range water reducer while also lowering the long-term permeability of the hardened concrete.
For Indian site teams the appeal is practical. Most basements, water tanks, sewage and effluent treatment plants (STP/ETP), podium slabs and retaining walls in the Delhi NCR and pan-India market specify M30 and above, and the durability clauses increasingly call for a controlled, low water-cement ratio plus a permeability limit. Rather than dosing a plain superplasticiser and then a separate waterproofing compound, Conplast WP320 addresses both demands from a single admixture. By dispersing the fine cement particles more effectively, it allows the same workability at a much lower water content, which is the single biggest lever on the strength and durability of structural concrete.
The chloride-free chemistry is important in the Indian context, where reinforcement corrosion driven by chlorides is a leading cause of premature distress in coastal, basement and water-contact structures. Being chloride-free, the product is safe for reinforced and prestressed concrete and does not introduce a corrosion risk of its own. The “integral” nature of the protection is the other headline benefit: because the permeability reduction is distributed through the full body of the concrete, it is not lost if a surface membrane is later punctured, abraded or detailed badly at penetrations and construction joints.
Conplast WP320 is best understood as a workability-strength-durability tool rather than a standalone tanking system. Fosroc’s own literature for the wider WP/waterproofing range is explicit that such admixtures do not make poor-quality concrete waterproof; they reward good mix design, well-graded aggregate, adequate cement content, proper compaction and disciplined curing. Used that way, it is a cost-effective route to dense, low-permeability structural concrete on Indian projects.
The technical insight
The dual action is the key to understanding WP320. The superplasticising fraction is a dispersant system (Fosroc’s comparable Conplast SP admixtures are based on sulphonated naphthalene polymers) that breaks up flocculated cement grains, freeing trapped water and letting the operator remove water while holding slump. Cutting the water-cement ratio is what physically reduces permeability: a lower w/c means fewer and finer capillary pores in the cement paste, so there is simply less continuous pore network for water to travel through. On top of that, the permeability-reducing component densifies and blocks the residual capillaries, compounding the effect. This is why the product is positioned as “integral” waterproofing rather than a surface barrier. Two consequences matter on site. First, the benefit is only realised if the freed-up water is actually taken out of the mix at the same slump; if the batcher instead lets workability balloon, you get the plasticising benefit but lose the permeability and strength gain and risk segregation. Second, like all naphthalene-based high-range reducers, a gross overdose tends to increase retardation and can entrain extra air, so dosage must be dialled in by trial mix, not copied from another job.
Where it is used
- Reinforced and mass concrete for basements, lift pits and below-grade structures requiring low permeability
- Water-retaining structures: overhead and underground water tanks, reservoirs, swimming pools
- Sewage and effluent treatment plant (STP/ETP) tanks, channels and clarifiers
- RC flat roofs, podium decks and terrace slabs exposed to standing water
- Retaining walls, box culverts, tunnels and other water-excluding structures
- High-strength, water-reduced structural concrete (M30 and above) where durability is specified
- Ready-mixed and precast concrete needing improved cohesion, pumpability and reduced permeability
- Marine and coastal RCC where chloride-free, low-permeability concrete is required
Key advantages
- Chloride-free, so safe for reinforced and prestressed concrete with no added corrosion risk
- Dual function: high-range water reduction plus integral permeability control from one admixture
- Enables major water:cement ratio reductions, raising compressive strength without extra cement
- Integral protection is distributed through the concrete and survives local surface damage
- Improved cohesion and particle dispersion minimise segregation and bleeding and improve pumpability
- Holds workability longer than ordinary sulphonated melamine/naphthalene admixtures
- Liquid form disperses instantly in water for easy, accurate dispenser batching
- Compatible with OPC, PPC and cement replacements such as PFA, GGBFS and microsilica, and with certain Fosroc surface coatings
Limitations & considerations
- Not a standalone tanking system; will not make poorly designed or poorly compacted concrete waterproof
- Performance depends on actually removing water at constant slump, well-graded aggregate, adequate cement content and good curing
- Gross overdose can cause increased retardation and additional air entrainment, reducing strength
- Must be added to the mixing water, never poured neat onto dry cement
- Optimum dosage is mix-specific and must be established by trial mixes, not assumed
- With alkali-reactive aggregates, high dosages of naphthalene-based admixtures can add undesirable alkalis; check before use
- Construction and movement joints still need a separate waterstop/sealing system; the admixture treats the concrete body, not the joints
Selection & best practice
Use a low, controlled water-cement ratio and take the water reduction the admixture allows at constant slump rather than letting workability rise. Specify well-graded aggregate and an adequate minimum cement content (the Fosroc WP literature recommends not less than about 350 kg/m3 for moderate grades). Always add Conplast WP320 to the gauging water through a calibrated dispenser, add each admixture separately if combining with other Conplast products, and confirm the final dosage by trial mix using the actual site materials. Detail construction joints with a proven waterstop (for example Fosroc Supercast) and maintain disciplined wet curing with water spray, wet hessian or a Concure curing membrane, especially in hot Indian conditions.
Specifications
| Product type | Chloride-free superplasticising and permeability-reducing concrete admixture |
| Chemical basis | Formulated blend of dispersants and permeability-reducing agents (naphthalene-based dispersant system) |
| Appearance | Brown liquid / solution that disperses instantly in water |
| Chloride content | Nil (chloride-free) |
| Specific gravity | Typically ~1.10-1.20 (verify against current local TDS; WP-range value ~1.10 at 20 C, SP430 ~1.20 at 20 C) |
| Air entrainment | Typically less than ~2% additional air at normal dosages (naphthalene superplasticiser range; confirm on TDS) |
| Typical dosage | Mix-specific, established by trial; WP/SP family typically ~0.5-2.0 litres per 100 kg of cementitious material |
| Compatible cements | All Portland cements (OPC) and cement replacements such as PFA, GGBFS and microsilica |
| Standards (family basis) | Conplast superplasticisers in this family comply with ASTM C494 (Type A/F) and BS 5075; confirm exact WP320 compliance on the country-specific datasheet |
| Storage / shelf life | Family minimum shelf life ~12 months stored between 2 C and 50 C (verify on WP320 TDS) |
| Flammability | Water-based, non-flammable |
Industry use cases
Commercial basements (Delhi NCR)
Deep multi-level RCC basements and lift pits below the water table use WP320 to achieve low-permeability, low w/c concrete that resists hydrostatic water ingress, backed up by waterstops at construction joints.
Water and wastewater
Municipal water tanks, reservoirs and STP/ETP structures rely on the chloride-free, dense concrete for both watertightness and resistance to aggressive moisture, reducing leakage and long-term repair.
High-rise podium and roof slabs
Podium decks, terrace and flat-roof slabs subject to ponding water benefit from integral permeability reduction that is not lost if the surface waterproofing membrane is later damaged.
Infrastructure and tunnels
Retaining walls, box culverts and tunnel linings use the water-reduction to hit high grades while keeping permeability low for durability in continuously damp ground conditions.
Precast and ready-mix
RMC suppliers and precast yards use the improved dispersion and pumpability to place dense, cohesive concrete with less bleeding and segregation, while meeting durability specs.
Frequently asked questions
Is Fosroc Conplast WP320 a waterproofing membrane or an admixture?
Does WP320 contain chlorides? Is it safe for reinforced concrete?
How does an admixture make concrete waterproof?
What is the correct dosage and how is it added?
Will WP320 make any concrete waterproof on its own?
How does Conplast WP320 compare with Conplast WL or Conplast Crystalline?
How we position Fosroc Conplast WP320
Within Fosroc’s own range, Conplast WP320 sits between the pure superplasticisers (Conplast SP430/SP432/SP500) and the dedicated integral-waterproofing products (Conplast WL, WL Xtra and Conplast Crystalline). Choose WP320 when a project needs strong water reduction and higher strength alongside lower permeability; choose Conplast WL/WL Xtra when the priority is straightforward hydrophobic integral waterproofing of plaster and concrete, or Conplast Crystalline when self-healing of hairline cracks is wanted. For surface and structural waterproofing that the admixture cannot provide, it is normally paired with Fosroc membranes/coatings (such as Brushbond or Proofex systems) and Supercast waterstops at joints. Against competitor admixtures, WP320 competes with Sika’s water-reducing and WT (Watertight Concrete) admixtures, Master Builders Solutions (MBS) MasterGlenium/MasterLife ranges, Dr. Fixit integral waterproofing admixtures (Pidiproof/water-reducing range) and STP’s integral waterproofing compounds. Space Arc Engineering, as an authorised Fosroc distributor in Delhi NCR and pan-India, can advise on whether WP320 or an alternative Fosroc product best matches a given specification, and always recommend confirming the final selection and dosage against the current region-specific technical data sheet and a site trial mix.
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