The northeast monsoon hits Chennai in October-November and every year, the same problem walls light up our WhatsApp inbox: damp patches on the ceiling, peeling paint near windows, water seeping through bathroom walls. Almost all of it is preventable with the right waterproofing done at the right stage.
This is the checklist we share with contractors who order from us, organised by where in the home you need to apply what.
TL;DR — the 4 critical areas
| Area | Product | When to apply |
|---|---|---|
| Roof slab (RCC) | Dr. Fixit LW+ in concrete mix + Pidifin 2K coating after curing | At pour + 28 days after curing |
| Bathroom & kitchen sunken slabs | Dr. Fixit Pidifin 2K (two-coat) | Before tile laying |
| External walls | Dr. Fixit Crack-X for cracks + a good exterior emulsion | After plastering, before painting |
| Underground / overhead tanks | Conplast WP200 admixture in concrete | At construction |
1. Roof slab — the #1 source of leaks
A leaking roof slab is the most common monsoon complaint, and it's almost always because the slab wasn't waterproofed during pouring. The standard fix is integral waterproofing — adding a liquid additive to the concrete mix itself so the whole slab becomes water-resistant.
Product: Dr. Fixit Pidiproof LW+ (1L, 5L, 10L, 20L sizes available)
How to use: Add 200ml of LW+ per 50kg cement bag at mixing. That's all. The contractor does this on-site as the concrete mixer is loading.
Cost: ~₹30 extra per square foot of slab. A 1000 sqft roof costs you ₹30,000 extra and saves you ₹200,000+ in re-plastering and re-painting over the next decade.
For an existing slab that's already leaking, you'll need to apply Dr. Fixit Pidifin 2K on top — but that's a remedial fix, not a substitute for getting it right at pour.
2. Bathroom & kitchen sunken slabs
Every bathroom in a multi-storey building should have its sunken slab waterproofed before tiles go down. Skipping this is the #2 cause of "the family below complains about a wet patch on their ceiling".
Product: Dr. Fixit Pidifin 2K — a cement-based two-component coating
Coverage: 1.5 kg per square metre, two coats. A typical 4'×6' bathroom needs about 6 kg total.
Process:
- Clean the concrete slab — no loose material, dust or grease
- Mix Pidifin 2K (Part A liquid + Part B powder) to a paint-like consistency
- Brush on first coat across slab, up walls by 6 inches
- After 4-6 hours, apply the second coat perpendicular to the first (this is key — covers any pinholes)
- Cure 24 hours before water testing, then 48 hours before tile work
3. External walls — manage cracks before they cause leaks
Chennai's temperature swings cause hairline cracks in plaster. During monsoon, those cracks become water channels. By March-April every year, treat them proactively.
Product for cracks: Dr. Fixit Crack-X Paste — apply directly into cracks up to 5mm wide with a putty knife.
Product for the wall surface: A waterproof exterior emulsion — Asian Paints Apex Weatherproof Exterior Emulsion is the workhorse. It bridges micro-cracks and resists rain.
Tip: After applying Crack-X, sand smooth, prime with Asian Paints Wall Primer, then paint. Don't skip the primer — Apex bonds to a primed surface 3× longer than to bare plaster.
4. Water tanks (overhead + underground)
Sintex / fibreglass tanks are usually fine. RCC tanks (the ones built into the structure) need waterproofing or they'll seep continuously.
Product: Fosroc Conplast WP200 — an admixture added to the concrete at construction. We stock this; contact us on WhatsApp for current prices.
For existing concrete tanks that are leaking from inside, the only fix is draining, drying, and applying a cementitious coating like Pidifin 2K.
The 5 most common mistakes we see
- Skipping the second Pidifin 2K coat. One coat looks fine — but pinholes that water finds within 6 months are guaranteed.
- Painting external walls without primer. Exterior emulsion adhesion drops 60%. Repaint every 2 years instead of 5.
- Using cement-sand mortar to seal cracks. Doesn't bond, will crack again. Use Crack-X.
- Waterproofing the bathroom slab after tiles are laid. You can't. Plan ahead.
- Mixing Dr. Fixit LW+ in the wrong ratio. The instruction says 200ml/bag. People add "a glug" by eye. Doesn't work.
Stock checklist before monsoon hits
If you're a contractor with active sites in Chennai, here's what to have on the truck by September:
- Dr. Fixit Pidiproof LW+ — 20L can per active foundation project
- Dr. Fixit Pidifin 2K — 5–15 kg packs (sized to bathroom count)
- Dr. Fixit Crack-X Paste — 1 kg tubs (carry 2-3 on every site)
- Asian Paints Apex Weatherproof — for any exterior repaint jobs
- Brushes, rollers, putty knives (we stock VIKI brand)
All of the above stocked at Suppliable Sholinganallur — delivered to your site in 60 minutes. Browse our construction chemicals →
Bottom line
Monsoon-proofing is cheap if you do it during construction, expensive if you do it after a leak. The total waterproofing cost on a 2000 sqft home is around ₹60,000–₹80,000 — about 1% of the build budget — and prevents 90% of the leaks you'd otherwise spend 10× fixing.
Got a monsoon-prep order coming up? WhatsApp us at +91 87786 27926 and we'll quote your full waterproofing BOM within the hour.