Anti-Seepage Chemicals: how to use it, and how much you need

Clean the surface down to sound concrete, cut out cracks in a V-groove and fill them, and make a 45-degree fillet (gola) at every wall-to-floor junction and around every pipe — that corner is where leaks start. Pre-wet the surface and bring it to saturated-surface-dry: damp, with no standing water. Mix the powder slowly into the liquid polymer with a slow-speed drill and paddle, let the slurry stand 5 to 10 minutes, and add no water at all. Brush the first coat well into the substrate so every pinhole is filled, lay the 45 GSM glass fibre mesh over the fillets while that coat is still wet, then apply the second coat 6 to 8 hours later at right angles to the first. Air cure 3 to 5 days under damp hessian, pond-test it, and only then lay the protective screed or tiles — within 24 to 48 hours of curing.

• Stiff nylon coating brush, 6 inchask us to source it
• Slow-speed drill with mixing paddleask us to source it
• Mixing bucket or drum, 20 litreask us to source it
• Wire brush and scraperask us to source it
• Hessian cloth for curingask us to source it
• Stiff nylon brushask us to source it

• Crack filling compound (Dr Fixit Crack X or similar)ask us to source it
• Polymer bonding liquid (Dr Fixit Pidicrete URP or similar)ask us to source it
• Glass fibre mesh, 45 GSMask us to source it
• Integral waterproofing admixture (Dr Fixit Pidiproof LW+)ask us to source it
• Cement for protective screed and filletsask us to source it
• 45 GSM glass fibre meshask us to source it
• Corner joint tapeask us to source it
• Pipe collarsask us to source it
• Cement for the spatter dash bond coatask us to source it

• Rubber glovesask us to source it
• Safety gogglesask us to source it
• Dust maskask us to source it
• Gum bootsask us to source it

• Ordering against the per-coat coverage instead of the finished figure. 1 kg does about 10 sq ft in one coat but only about 5 sq ft once both coats are on. Order on 5 sq ft per kg or you will be short by half.
• Adding water to make the mix spread further. The data sheet says do not dilute. Thinning drops the film thickness below the 1.2-1.5 mm the coating needs and it fails at the thin spots first, usually within one monsoon.
• Skipping the 45-degree fillet at the wall-floor junction and around pipe inserts. A coating turned up a sharp 90-degree corner cracks at the angle. Almost every sunken-area leak traced back starts here, not in the middle of the slab.
• Flooding the fresh coating with water to cure it, or doing the ponding test too early. Cure it under damp hessian for 3 to 5 days first. Water curing a green coating washes the polymer out.
• Leaving the coating exposed as the finished surface. On a terrace or anywhere with foot traffic it must be covered by a protective screed, or it abrades through and you have paid for nothing.

• Buy the complete two-component pack, never loose powder. Fastflex is sold as 12 kg (5 kg liquid polymer + 7 kg powder) or 48 kg. A shop that offers you powder by the kilo and tells you to add cement or water is selling you a wrong-ratio job that will not perform.
• Check the manufacturing date on the pack. Shelf life is 12 months from manufacture in a sealed container. Reject any bag where the powder has gone lumpy or set hard — it has already picked up moisture and will not disperse.
• Coverage is not comparable across brands, so compare on rupees per sq ft finished, not rupees per kg. Different makers specify different film thickness, and the honest spread across major Indian brands is roughly 3.4 to 7.5 sq ft per kg over two coats — more than double. Read the coverage line on the pack before you compare prices.
• Do not let a dealer substitute grades on price. An integral admixture such as Pidiproof LW+ mixed into concrete, a crystalline powder such as Krystalline, and a surface coating such as Fastflex are three different systems solving three different problems. Counterfeit tins are common in the Kanpur market — buy from a listed dealer, check the seal and the printed batch number.