Balconies are small, and their leaks are not. A failed balcony wets the bedroom wall behind it, the slab below, and the neighbour's ceiling — because a balcony is really a tiny terrace with worse drainage and a door in exactly the wrong place. The fix is terrace discipline at balcony scale.
Why balconies fail
- The fall is wrong or absent. A few square metres with no slope holds a puddle against the building at every rain.
- The door threshold leaks inward. The junction between balcony floor and room floor is the least-glamorous, most-consequential detail — water wicks under the track into the inside flooring.
- The floor–wall junctions crack. Same as terraces: right angles move and open (the junction logic).
- The drain is an afterthought. One small spout, often blocked, often set high, serving the whole floor.
- Planters. Standing pots hold permanent damp discs against the slab — the balcony's private monsoon.
The sequence
- Water-test the fall: a bucket poured at the door should reach the drain, promptly, all of it. If not, the screed is corrected first — no coating fixes a puddle.
- Prepare: tiles up if hollow, surface cleaned to sound, cracks cut and filled.
- Detail the perimeter: coved fillets at floor–wall junctions; the coating turned up walls and parapet to splash height.
- Detail the threshold: the barrier carried up and under the door line so the room floor sits behind a sealed step — the detail that separates professionals from painters.
- Collar the drain where spout meets slab; then coat the whole floor as one tray with a suitable polymer-modified system.
- Cure, flood-test for a day, then finish — tiles or wearing surface per the system.
Living with a waterproofed balcony
Keep the drain mouth clear monthly in season; stand planters on feet, not on the slab; and treat the first hairline at the junction as maintenance, not decay (the yearly habit).
Frequently asked questions
The bedroom wall beside the balcony shows damp. Balcony's fault?
Most often — threshold or junction. Photograph both sides and send them over; the pattern usually names the path.
Can I just seal the tile joints?
Grout sealing is grooming, not waterproofing — hairlines re-open. If water is moving, the tray needs doing properly once.