Frequently Asked Questions

How does Fosroc Conplast WL reduce concrete permeability and is the hydrophobic mechanism effective for concrete in permanent contact with water (positive hydrostatic pressure)?

Fosroc Conplast WL reduces concrete permeability through two complementary mechanisms — the water-cement ratio reduction mechanism and the hydrophobic pore treatment mechanism — and it is important to understand the limitations of each mechanism for concrete in permanent contact with water under positive hydrostatic pressure. The water-cement ratio reduction mechanism: every unit reduction in the water-cement ratio of concrete produces a measurable reduction in the volume fraction of capillary porosity in the hardened cement paste, because the capillary pores are the unreacted volume created by excess water above that needed for cement hydration; at a water-cement ratio of 0.55 (typical M20 concrete mixed without admixture), the capillary porosity is high and the concrete is quite permeable; reducing the w/c ratio to 0.45 or 0.40 with the water-reducing component of Conplast WL significantly reduces capillary porosity and permeability — this mechanism is permanent and effective in all wet conditions including sustained hydrostatic pressure. The hydrophobic pore treatment mechanism: the hydrophobic fatty acid or polymer component of Conplast WL coats the walls of the concrete capillary pores with a hydrophobic layer that repels water and reduces capillary suction (the capillary suction mechanism draws water into the concrete under negative pressure, i.e., from a dry surface toward the interior under osmotic and capillary tension); this mechanism is effective in reducing water absorption in concrete that dries and rewets (rain exposure, splash zone) — the hydrophobic coating reduces the rate at which water is absorbed into the capillary pores from the exposed concrete surface; however, under sustained positive hydrostatic pressure (groundwater pressure from the outside of a permanently submerged basement wall), the hydrostatic pressure exceeds the capillary tension and forces water through the capillary network regardless of the hydrophobic coating on the pore walls — the hydrophobic mechanism provides limited benefit under sustained hydrostatic pressure. In summary: Conplast WL is an excellent admixture for concrete in intermittent water contact (rain exposure, splash, wet/dry cycling) and for improving baseline concrete durability in below-grade applications; for concrete under sustained positive hydrostatic pressure (permanent water table above floor level), the lower w/c ratio from Conplast WL provides benefit but the hydrophobic mechanism alone is not sufficient — external membrane waterproofing (Proofex 30, Nitoproof 400) is required for reliable waterproofing performance.

Can Fosroc Conplast WL and Fosroc Conplast SP (superplasticizer) be used together in the same concrete mix for a high-performance water-retaining concrete mix and what is the correct order of addition?

Yes — Fosroc Conplast WL and Fosroc Conplast SP (or Conplast SP430 PCE superplasticizer) can be used together in the same concrete mix to combine the integral waterproofing function of Conplast WL with the high water reduction and workability of the superplasticizer. This combined admixture approach is used for high-performance water-retaining concrete mixes where both low permeability (from reduced w/c ratio and hydrophobic treatment) and high workability for pump placement and compaction in congested reinforcement are required. The benefits of the combined use are additive: Conplast WL provides the hydrophobic integral waterproofing function and a moderate 5 to 12 per cent water reduction; Conplast SP provides an additional 10 to 15 per cent water reduction (SNF type) or 20 to 25 per cent (PCE type, SP430) on top of the WL base reduction; the combined water reduction at the same workability target can achieve a w/c ratio of 0.35 to 0.42 for well-designed mixes — very low permeability concrete approaching Type B waterproof concrete quality. The admixture compatibility and order of addition: Conplast WL and Conplast SP are compatible admixtures when used together in concrete at normal dosages — there is no adverse chemical interaction between the lignosulphonate water reducer in WL and the SNF or PCE superplasticizer in SP; the correct order of addition at the batching plant is to add Conplast WL to the mix water first (or add it directly to the mixer with the mix water as part of the gauging water batch), then add Conplast SP as the last admixture, after all other ingredients are in the mixer; always confirm the specific compatibility of the exact products and dosages to be used on your project by requesting a compatibility trial from the Fosroc technical team, as different cement-admixture combinations can behave differently and a site trial at the batching plant is always the recommended practice before committing to the full production volume.

What is the difference between Fosroc Conplast WL and Fosroc Proofex Integral in terms of performance and which should be specified for an overhead water storage tank construction project in India?

Fosroc Conplast WL and Fosroc Proofex Integral both serve as integral concrete waterproofing admixtures added to the concrete at the batching stage, but they operate on different chemical mechanisms and have different primary performance characteristics — the selection between them depends on the specific waterproofing performance requirement, the concrete mix design, and the type of structure. Conplast WL (combined water reducer plus hydrophobic waterproofer): mechanism — dual action of water reduction (reducing w/c ratio) and hydrophobic pore coating (reducing capillary suction); primary benefit — water reduction (5 to 12 per cent) plus hydrophobic treatment; best for — concrete exposed to rain, splash, and intermittent wet-dry cycling where the hydrophobic mechanism is most effective; the w/c ratio reduction provides permanent durability improvement across all wet conditions; limitations — hydrophobic mechanism is less effective under sustained hydrostatic pressure compared to water-cement ratio reduction alone. Proofex Integral (pure hydrophobic polymer integral waterproofer): mechanism — hydrophobic polymer system that coats pore walls without contributing water reduction; primary benefit — concentrated hydrophobic pore treatment at higher polymer dose than in Conplast WL; best for — very high hydrophobic activity in water-absorbing concrete (brick, blockwork, pre-existing concrete); limitations — does not reduce water demand and therefore does not reduce w/c ratio; relies entirely on the hydrophobic coating mechanism. For an overhead water storage tank in India: the primary waterproofing mechanism needed is impermeability at the concrete face in contact with stored water at positive hydrostatic head — the interior face is under water pressure for the entire service life; the correct specification is Conplast WL in the concrete mix (providing the water-cement ratio reduction and hydrophobic treatment as a combined admixture), used together with a compatible superplasticizer for a total w/c ratio of 0.40 to 0.45, and combined with an external brush-applied crystalline waterproofing coating (Cemseal) on the internal concrete face after curing — the crystalline coating provides the positive-face waterproofing and the Conplast WL in the concrete provides the backup impermeability throughout the concrete cross-section.