5-Step Terrace Waterproofing System to Prevent Ceiling Dampness During Heavy Rains
In Kolkata, flat concrete roofs expand under 42°C summer heat and contract rapidly during sudden monsoon downpours. This severe thermal shock cracks rigid concrete, allowing water to seep through reinforcement bars and cause rusting and spalling.
The Modern 5-Step Waterproofing Protocol
Step 1 — Substrate Preparation: Mechanically grind loose laitance, open honeycombs, and clean all dust with high-pressure air.
Step 2 — Fillet Coving: Cast concave 45-degree angle fillets at all roof-to-parapet wall joints using polymer-modified mortar.
Step 3 — First Slurry Coat: Apply a 2-component acrylic polymer-modified cementitious elastomeric slurry across the surface.
Step 4 — Mesh Reinforcement: Embed 45 GSM alkali-resistant fiberglass mesh into the wet first coat across all corners and expansion joints.
Step 5 — Second Cross Coat: Apply the second slurry coat perpendicular to the first, achieving a minimum 1.5 mm dry film thickness (DFT).
- Perform a 72-hour ponding water test with 50 mm standing water before casting the protective screed.
- Top the waterproofing with solar reflective tiles or a protective slope screed to reflect summer heat and shed rainwater quickly.