A leaking terrace is one of the most common and frustrating problems in Indian homes. Damp patches, peeling paint and dripping ceilings usually start from a roof that was never properly waterproofed, or one whose protection wore out. The best time to fix it is in the dry months before the monsoon arrives.
Step 1: find out why the roof leaks
- Ponding water because the slope is too flat or outlets are blocked.
- Cracks in the slab or old screed from heat expansion.
- Joints where the slab meets parapet walls, water tank bases and pipes.
- Failed old coatings that have blistered or peeled.
Pour a bucket of water on the roof on a dry day and watch where it collects. Those spots will show you the problem areas.
Step 2: choose a waterproofing system
| System | How it works | Good for | Typical life* |
|---|---|---|---|
| Cementitious coating | Polymer-modified cement slurry brushed in two coats | Budget work, wet areas, under tiles | Shorter on exposed roofs |
| Liquid elastomeric membrane (acrylic or polyurethane) | Flexible rubber-like coating that bridges fine cracks | Exposed terraces with movement | Medium to long |
| Bituminous sheet membrane | Rolls of modified bitumen torched or self-adhered | Large flat roofs | Long, if protected from sun |
| Brickbat coba | Traditional broken-brick and lime/cement layer laid to slope | Adds slope and insulation | Long, but heavy |
*Life depends heavily on surface preparation, product quality and sun exposure. Ask the applicator for a written warranty and the product's datasheet.
Step 3: prepare the surface properly
Most waterproofing failures are preparation failures. The surface must be clean, sound and dry enough for the product chosen. Loose screed is broken out, cracks are opened up and filled, and dust and old flaking coatings are removed.
Step 4: treat joints and corners first
- Form a rounded fillet, called a coving, where the roof meets parapet walls. Sharp corners crack.
- Carry the membrane up the parapet by about 300 mm.
- Seal around every pipe and outlet with fabric reinforcement embedded in the coating.
Step 5: get the slope and drainage right
A flat roof should still slope towards outlets, commonly around 1 in 100. Outlets need grates to stop leaves blocking them, and there should be enough of them so that water clears quickly after heavy rain.
Bonus: cool the roof at the same time
A white, heat-reflective top coat reduces how hot the roof slab gets, which also lowers temperatures in the room below. Our guide to keeping homes cool in a heatwave explains why.
Frequently asked questions
Can I waterproof during the rains?
Most coatings need a dry surface and several dry days to cure. Emergency patches are possible, but permanent work is best done in the dry season.
Should I remove old tiles before waterproofing?
If tiles are hollow, cracked or debonded, yes. Coating over loose tiles traps water and fails quickly.