About Fosroc Conplast UW-L

Fosroc Conplast UW-L is a chloride-free, ready-to-use liquid anti-washout admixture engineered specifically for underwater concreting. Unlike a superplasticiser, it does not work by dispersing cement; instead it is a gel-forming (viscosity-modifying) cohesion admixture. When dosed into the mix it generates a gel within the water phase that surrounds the cement particles, holding the mix together and shielding the fines from being washed out as the concrete falls through and settles under water. The result is concrete that stays cohesive during placement, with minimal loss of cement, minimal laitance and a sound, dense set.

The performance gain is quantifiable. In an ordinary concrete mix placed under water, washout can carry away up to roughly 30% of the fines content — a direct loss of cement, strength and durability. With Conplast UW-L incorporated into the same mix, that washout is reduced to less than 6%, keeping the binder where it belongs. Crucially, the admixture achieves this cohesion without delaying the chemistry of the concrete: stiffening is achieved soon after placing and the set time of the concrete is not affected.

Conplast UW-L is supplied as a liquid with a specific gravity of 1.010 and a chloride content of Nil to BS 5075, making it suitable for reinforced and prestressed underwater work. It should not be confused with the powder grade Conplast UW, which is a chloride-free blend of polymers supplied as a fine brown powder; UW-L is the ready-to-use liquid form preferred where on-site batching of a liquid admixture is more practical. It is compatible with all Portland cements plus replacement materials such as microsilica, GGBS and fly ash, and is recommended for use alongside Fosroc’s Auramix series PCE admixtures. As an authorised Fosroc distributor and applicator across Delhi NCR and Pan-India, Space Arc Engineering supplies Conplast UW-L with technical support and on-site trial guidance for Indian marine, bridge and tremie-concrete projects.

The technical insight

Conplast UW-L is a viscosity-modifying / gel-forming cohesion admixture, not a plasticiser. It thickens the water phase of the mix so the cement and fines are physically held against the washing action of water, rather than chemically dispersing the cement the way an SNF or PCE superplasticiser would. Because it modifies cohesion and not the hydration reaction, stiffening occurs soon after placing and the overall set time of the concrete is unaffected. For workability, it is designed to be paired with a PCE superplasticiser — Fosroc recommends the Auramix series — so the mix can be made flowable and self-levelling for tremie or pumped placement while Conplast UW-L supplies the anti-washout cohesion. With a specific gravity of 1.010, dosing volumes are close to dosing by mass, and the normal dosage of 0.3 litres per 100 kg of cementitious materials should always be confirmed by site trials, since over- or under-dosing can be required to suit the specific mix design, placement method and water conditions.

Where it is used

• Tremie concrete placed under water for piles, pile caps and pier foundations
• Marine and port structures — quay walls, jetties, breakwaters and harbour works
• Bridge substructures: pier footings and cofferdam concrete poured below the water line
• Diaphragm walls and bored cast-in-situ piles
• Underwater repairs and patching of submerged concrete elements
• Cut-off walls, intake structures and other below-water-table civil works

Key advantages

• Reduces underwater washout of fines from up to ~30% to less than 6% in the same mix, preserving cement, strength and durability
• Chloride-free (Nil to BS 5075), so it is suitable for reinforced and prestressed concrete
• Ready-to-use liquid — convenient on-site batching with no need to pre-disperse a powder
• Does not delay setting: stiffening is achieved soon after placing and concrete set time is not affected
• Compatible with all Portland cements plus microsilica, GGBS and fly ash replacements
• Works in tandem with Fosroc Auramix PCE admixtures to deliver flowable, cohesive, washout-resistant concrete
• Non-flammable with a minimum 12-month shelf life when stored correctly

Limitations & considerations

• Not a superplasticiser — it provides cohesion, not workability, and is normally combined with a PCE admixture to achieve flow
• Dosage must be confirmed by site trials; the 0.3 L/100 kg cementitious figure is a starting point that may need adjustment for the mix and placement method
• Compatibility with plasticisers other than the recommended Fosroc Auramix series should be checked with Fosroc before use
• Performance depends on a correctly designed underwater mix; it cannot compensate for an unsuitable mix design or poor placement practice
• Liquid must be protected from frost during storage to maintain shelf life and performance

Selection & best practice

Specifications

Industry use cases

How we position Fosroc Conplast UW-L

Specialist anti-washout admixture within the underwater-concreting segment. Sits alongside Fosroc’s Auramix PCE superplasticisers (used together) and the powder-grade Conplast UW. Comparable products from other suppliers include BASF MasterMatrix UW range and Sika UCS / Sika anti-washout admixtures; Space Arc Engineering leads with Fosroc as an authorised distributor and applicator across Delhi NCR and Pan-India.

Related Concrete Admixtures products

View all Concrete Admixtures products →