Fosroc Conplast WP
Chloride-free hydrophobic, pore-blocking integral waterproofing admixture that drastically reduces water absorption in structural and precast concrete — supplied and applied by Space Arc Engineering, your authorised Fosroc distributor across Delhi NCR and Pan-India.
What is it?
Fosroc Conplast WP400 is a chloride-free organic liquid integral waterproofing admixture. It works by hydrophobic pore-blocking — reacting with the products of cement hydration to produce a water-repellent material inside the concrete that resists the absorption of external water.
Where is it used?
Below-ground and water-retaining structures, marine reinforced concrete, piles, manholes, precast units, and wastewater treatment and desalination plants — wherever dense, low-absorption concrete is specified.
Why use it?
Dosed into the mix, it reduces water absorption of the hardened concrete while remaining chloride-free to BS 5075, making it safe for use in reinforced concrete without risk of accelerating steel corrosion.
How is it applied?
Added to the concrete at a normal dosage of 1.5 to 2.0 litres per 100 kg of cement, with the optimum determined by site trial. It disperses instantly in the mix water and is incorporated during normal batching.
About Fosroc Conplast WP
Fosroc Conplast WP400 is an integral waterproofing admixture for concrete and mortar, supplied as a chloride-free organic liquid that appears as a turbid solution and disperses instantly in water. It is added during batching to densify the concrete from within, rather than being applied as a surface coating.
A note on naming: there is no Fosroc product catalogued under the bare name “Conplast WP.” Fosroc’s waterproofing-admixture range is numbered and suffixed — Conplast W, WL, WP20, WP90E, WP100, WP200, WP400, WP402, WP421 and WP500 — and each is a distinct chemistry for a distinct purpose. The hydrophobic, pore-blocking chemistry described on this page is that of Conplast WP400, so the product has been correctly identified here as Conplast WP400 to avoid confusion with, for example, Conplast WP20 (a lignosulphonate-based water-reducing type), which is a completely different material. If your specification or bill of quantities calls up a specific Conplast WP suffix, share it with our team and we will confirm the correct grade before supply.
Conplast WP400 functions by hydrophobic pore lining and partial pore blocking: the organic admixture reacts with the products of the cement hydration process to produce a hydrophobic material that repels external water and so reduces its absorption into the concrete. The result is a denser, more water-resistant matrix that helps protect the concrete and embedded reinforcement over the life of the structure. Because it is chloride-free to BS 5075, it carries no risk of introducing chlorides that could promote corrosion of reinforcing steel — an important consideration for the marine, below-ground and water-retaining works where this product is most often specified.
For Indian projects, Space Arc Engineering supplies genuine Fosroc Conplast WP400 as an authorised distributor and applicator, with technical support on dosage trials, batching and compatibility for sites across Delhi NCR and Pan-India.
The technical insight
The performance of Conplast WP400 comes from chemistry, not from blocking the mix with fine fillers. As the cement hydrates, the admixture reacts with the hydration products to deposit a hydrophobic, water-repellent material that lines and partially blocks the capillary pores of the concrete. Water that would otherwise be drawn into those capillaries by absorption is instead repelled, which is why the product is described as a hydrophobic, pore-blocking integral waterproofer rather than a simple densifier.
This is verified by water-absorption testing: in the official data, water absorption is reduced to below 1.0%, measured by SS78:Part A22:1987. The admixture is chloride-free to BS 5075, so it can be used in reinforced and prestressed concrete without contributing chlorides to the system. Note that BS 5075 (the admixture reference) and SS78:Part A22:1987 (the water-absorption test) are the correct standards for this product — distinct from basement-tanking application codes, which describe how a structure is waterproofed overall rather than how this admixture is classified.
A correctly designed mix still matters: WP400 reduces absorption but is not a substitute for good compaction, adequate cover, sound joints and proper curing. The optimum dosage within the 1.5-2.0 litres per 100 kg cement range should be fixed by trial against the actual mix, cement and aggregates being used.
Where it is used
- Below-ground structures such as basements, retaining walls and foundations
- Water-retaining structures including tanks, reservoirs and sumps
- Marine reinforced concrete and structures exposed to seawater
- Piles and other cast-in-situ buried concrete elements
- Precast concrete units requiring low water absorption
- Manholes, inspection chambers and underground service structures
- Wastewater treatment plant structures
- Desalination plant concrete
Key advantages
- Chloride-free to BS 5075 — safe for use in reinforced and prestressed concrete with no added corrosion risk to steel
- Hydrophobic pore-blocking action drastically reduces water absorption of the hardened concrete
- Integral protection cast into the full thickness of the concrete, not a surface layer that can be damaged or worn away
- Water absorption reduced to below 1.0% (measured by SS78:Part A22:1987)
- Disperses instantly in the mix water for straightforward batching
- Suited to demanding exposure — marine, below-ground, water-retaining and effluent environments
- Genuine Fosroc product supplied with technical and applicator support across Delhi NCR and Pan-India
Limitations & considerations
- Not a standalone tanking system — for full basement or below-ground waterproofing it should be combined with appropriate membranes, joint detailing and surface systems as the design requires
- Performance depends on a well-designed, well-compacted and properly cured concrete mix; it does not compensate for poor workmanship, inadequate cover or unsealed joints
- Optimum dosage must be established by site trial within the recommended range against the specific mix, cement and aggregates
- Reduces but does not eliminate water absorption — it lowers permeability rather than rendering concrete fully impermeable
- ‘Conplast WP’ is not a valid Fosroc SKU; always confirm the exact suffixed grade (WP400 here) against the project specification before ordering
- Refer to the current Fosroc technical data sheet and material safety data sheet for storage, shelf life, handling and full application detail
Selection & best practice
Establish the optimum dosage by trial within the 1.5 to 2.0 litres per 100 kg of cement range, using the actual cement, aggregates and mix design for the job. Add Conplast WP400 to the mix water or the gauged batch so it disperses evenly — it disperses instantly in water — and avoid adding it to dry cement. Maintain good compaction, adequate cover to reinforcement and thorough curing, since the admixture works alongside a sound mix rather than replacing good concrete practice. For below-ground and water-retaining works, integrate WP400 with the project’s membrane, waterstop and joint-sealing details rather than relying on the admixture alone. Always confirm the exact Conplast WP grade against the specification before ordering, and request the current Fosroc TDS for storage, shelf life and handling guidance.
Specifications
| Chemical base / type | Chloride-free organic liquid; hydrophobic pore-blocking integral waterproofing admixture that reacts with cement hydration products to produce a hydrophobic material repelling external water |
| Appearance | Turbid solution (instantly disperses in water) |
| Specific gravity | Typically 1.05 at 20 C |
| Dosage | Normal recommended dosage 1.5 to 2.0 litres per 100 kg of cement (optimum by trial) |
| Chloride content | Nil, to BS 5075 |
| Standards | BS 5075 (chloride content); water absorption below 1.0% measured by SS78:Part A22:1987 |
| Primary use | Reduces water absorption in structural and precast concrete — below-ground structures, marine RC, piles, water-retaining structures, manholes, wastewater treatment and desalination plants |
Industry use cases
Below-ground & water-retaining
Basements, retaining walls, water tanks, reservoirs and sumps where concrete must resist continuous water contact and reduced absorption is specified.
Marine & coastal
Marine reinforced concrete and seafront structures where chloride-free admixture chemistry is essential to avoid adding corrosion risk to embedded steel.
Infrastructure & foundations
Bored and cast-in-situ piles and buried foundation elements requiring low-permeability, durable concrete.
Water & wastewater
Wastewater treatment plant structures, manholes and desalination plant concrete that must withstand aggressive, water-saturated service conditions.
Precast manufacturing
Precast units batched for low water absorption and improved durability, dosed at a trial-optimised rate during production.
Frequently asked questions
Is there a Fosroc product simply called ‘Conplast WP’?
How is Conplast WP400 different from Conplast WP20?
What is the recommended dosage of Conplast WP400?
Does Conplast WP400 contain chlorides?
What standards and test values apply to Conplast WP400?
Can Conplast WP400 waterproof a basement on its own?
Does Space Arc supply genuine Fosroc Conplast WP400 in Delhi NCR?
How we position Fosroc Conplast WP
Lead-with-Fosroc product page for the construction-chemicals admixtures category. Positions Space Arc Engineering as the authorised Fosroc distributor and applicator for Conplast WP400 across Delhi NCR and Pan-India, correcting the earlier mislabelled ‘Conplast WP’ page to the real WP400 SKU. Within Fosroc’s own range, WP400 sits alongside other Conplast WP-series integral waterproofers (WP20, WP100, WP200, WP421, WP500); where a buyer is comparing brands, credible alternative integral waterproofing admixtures in the Indian market include Sika WT-200 P / Sika-1, Dr. Fixit Pidiproof LW+ and MC-Bauchemie integral admixtures — Space Arc can advise on the right grade for the specification.
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Authorised distribution, technical advice & professional application across Delhi NCR and Pan-India.