Why NCR terraces crack and leak
Concrete and screed expand in peak summer and contract in winter. Over a few years this movement opens hairline cracks, especially at the wall-slab junction, around pipe penetrations and along old joints. Monsoon water then finds those paths. Add blocked drains and poor slope, and water stands on the roof for days.
Step 1: Inspect before choosing a product
A proper inspection looks at four things: the slope toward outlets, the condition of existing coating or tiles, cracks and joints, and drainage. The cause decides the system. Choosing a product first and the problem second is the most common reason treatments fail.
Step 2: Prepare the surface
- Remove loose, hollow or deteriorated screed and old failed coatings.
- Clean the surface of dust, oil and algae.
- Repair cracks and spalled areas with a polymer-modified repair mortar.
- Form a cove (a rounded fillet) at the wall-slab junction so the membrane is not stretched over a sharp corner.
- Fix or re-seal pipe penetrations and outlets, since leaks often start here.
Roof slope should carry water to the outlets. A gentle slope, commonly around 1 in 100, is used. Where the slope is poor, a corrective screed is laid before waterproofing.
Step 3: Choose the system
| System | Where it suits | Points to know |
|---|---|---|
| Cementitious or polymer-modified coating | Bathrooms, tanks, protected terraces | Good bond, limited flexibility; needs a protective layer where movement is expected |
| Polyurethane liquid membrane | Exposed terraces and balconies | Flexible and seamless; follow the manufacturer's UV and protection guidance |
| Acrylic elastomeric coating | Roofs that need a reflective, flexible coat | Needs a clean, sound base and proper drying between coats |
| Bituminous or sheet membranes | Large roofs with a protective topping | Detail work at edges and joints decides performance |
Step 4: Apply in coats and detail the joints
Liquid membranes are applied in multiple coats, with reinforcement fabric at joints and corners. Coverage and thickness follow the product data sheet, not guesswork. Rushing coats or applying on damp surfaces causes blisters and early failure.
Step 5: Test before covering
Once the membrane has cured, the terrace is flooded with a few centimetres of water and left for a period commonly set at 24 to 48 hours, and the ceiling below is checked. Only after it passes is the protective screed, tile or paint applied.
Common mistakes
- Applying a coating over loose or damp screed.
- Skipping the cove and joint detailing.
- Ignoring drainage and slope.
- Covering the membrane before testing.
- Cutting or drilling the finished roof later for dish antennas, solar structures or railings without re-sealing.
If you plan rooftop solar, finish the waterproofing first and ask for mounting structures that do not puncture the membrane, or seal each fixing point properly.