1. The ceiling below turns damp after rain
The clearest sign. A patch on the top-floor ceiling that darkens after rain and fades in dry weather means water is getting through the slab. Note that the patch is rarely directly under the entry point; water travels along the slab and comes out at the weakest spot. Tracing it is part of roof and ceiling leakage repair.
2. Water stands on the terrace for hours
After rain, walk up and see where water collects. Puddles still there several hours later mark low spots where the slab is soaking water in. If they are next to the parapet or around a tank base, those are usually the first places to fail.
3. The old coating is peeling, powdery or lifting
Rub the surface with your hand. If it leaves a chalky powder, or the coating comes up in flakes or sheets, it has stopped protecting the slab. Anything new applied over it will come away with it, so the old coat has to be ground off first.
4. Hairline cracks across the slab or along the parapet
Daily heating and cooling opens fine cracks, often in a map-like pattern, and a straight crack along the line where the slab meets the parapet wall. Wider cracks, or cracks that also show on the ceiling below, may go through the slab and need crack repair or grouting rather than just a coating.
5. A hollow sound when you tap
Tap the terrace with a small hammer or the back of a key. Sound concrete rings solid; a dull, hollow sound means the top layer has separated from the slab underneath. Water collects in those voids. Hollow patches have to be chipped out and repacked before waterproofing.
6. Paint blistering on top-floor walls
Bubbles, flaking paint or a white salt line high up on top-floor walls often trace back to the parapet or the terrace edge, where water runs into the wall. It is easy to mistake for a wall problem and repaint, which does not last.
7. Rust stains or falling plaster on the ceiling
This is the late stage. Brown streaks, cracks following a straight line, or plaster falling off to show steel rods mean water has been reaching the reinforcement long enough for it to rust and expand. The slab needs repair as well as waterproofing, and leaving it makes it worse every season.
What to do if you see these signs
Take photos of the terrace and the ceiling below, ideally during or just after rain, and send them to us on WhatsApp. We can usually tell you from the photos what the job is likely to involve. Then book a site visit in the dry months so the coating can cure properly before the monsoon. A visit includes tapping for hollow patches, tracing cracks and measuring the area, followed by a written scope.
Read more about terrace waterproofing, the six steps we follow, and what decides the cost.