Frequently Asked Questions

What is the correct dosage and mixing procedure for Dr. Fixit Pidiproof LW+ in site-mixed concrete for a domestic terrace slab, and does adding Pidiproof LW+ eliminate the need for a separate waterproofing treatment on the terrace?

The correct procedure for incorporating Dr. Fixit Pidiproof LW+ into site-mixed concrete for a domestic terrace slab is as follows. Step 1 — Calculate dosage. For a standard terrace slab mix of M20 grade (1:1.5:3 cement:sand:aggregate ratio — 1 bag OPC cement per batch), the recommended dosage of Pidiproof LW+ is 200 ml per 50 kg bag of OPC cement. For a batch with one 50 kg bag of cement, add 200 ml (one measuring cup) of Pidiproof LW+ to the gauging water. For a concrete mixer batch using two bags of cement, add 400 ml of Pidiproof LW+ to the gauging water. Step 2 — Measure and add to gauging water. Measure the required Pidiproof LW+ quantity using a measuring jug or graduated container. Add it to the full measured quantity of gauging water in the water drum (or water drum measuring tap) before adding the water to the dry concrete mix. Do not add Pidiproof LW+ directly to the dry materials — it must be pre-mixed with the gauging water. Step 3 — Reduce mixing water. Because Pidiproof LW+ has a plasticising effect, the concrete mix will be slightly more workable than a standard mix without admixture. For the same target slump (100 to 125 mm for terrace concrete placed by hand), reduce the gauging water by approximately 10 percent (reduce 30 litres to 27 litres per bag of cement as a starting point, then adjust to achieve required workability at site). This water reduction is important — it maintains or improves the water-cement ratio and prevents the plasticiser effect from simply producing a wetter, weaker concrete rather than a denser, more workable one. Step 4 — Mix and place normally. Mix, compact, level, and finish the concrete slab as normal. Apply a curing compound (Dr. Fixit Curing Compound) or wet hessian curing for a minimum of 14 days after casting to ensure full hydration and maximum density. Regarding whether Pidiproof LW+ eliminates the need for surface waterproofing: No — integral concrete waterproofing admixtures like Pidiproof LW+ significantly reduce the permeability of the concrete body but do not eliminate the need for surface waterproofing treatment on a terrace slab. The flat terrace slab is subject to ponding water during monsoon rain (before and after drains clear), thermal cycling causing surface micro-cracking, and construction joints that are inherently weaker than the body concrete. For a domestic terrace, a complete waterproofing system consists of the Pidiproof LW+ integral admixture in the slab concrete (provides bulk waterproofing), plus a surface waterproofing membrane (Dr. Fixit 201 Acrylic or Pidifin 2K applied to the top face of the cured slab — provides surface crack bridging and additional waterproofing), plus a protective screed (40 to 50 mm thick waterproofed cement-sand screed with Pidiproof LW+ dosing laid over the membrane — protects the membrane and provides a smooth surface with adequate fall to drains). This three-layer system provides defence-in-depth waterproofing that is robust against the range of moisture risks facing Indian flat roofs.