A balcony that leaks into the room below is one of the most common problems in Sydney apartments and houses. It starts with a stain on the ceiling and, left alone, ends with concrete cancer, mould and a much bigger bill. Here is what causes it and how it should be fixed.
Why balconies leak
Balcony tiles and grout are not waterproof. The waterproofing is the membrane underneath. When that membrane fails, water passes through the tiles and bedding, into the slab and down to the ceiling or unit below. The usual causes are:
- A failed or missing membrane, often on older buildings or where tiles were replaced without re-waterproofing.
- Poor falls, so water sits on the balcony instead of draining away.
- Blocked or undersized drains, and no overflow when the drain cannot keep up.
- Missing waterstops at the door, letting water track back under the threshold.
- Movement cracking at slab edges and junctions that the membrane was not detailed to handle.
- Balustrade fixings drilled through the membrane without proper sealing.
Signs your balcony needs repair
- Stains, bubbling paint or drips on the ceiling below.
- Drummy, lifting or cracked tiles.
- White powdery salts (efflorescence) along grout lines or slab edges.
- Rust stains or cracking along the balcony edge.
- Water pooling for hours after rain.
- A loose or corroding balustrade.
Can you waterproof a balcony without removing tiles?
There are clear penetrating sealers and over-tile coatings sold for exactly this. They can help for a while on a balcony with minor, surface-level issues. But if water is already getting through to the slab, a sealer does not fix a failed membrane, poor falls or a bad outlet. In our experience, a balcony that is actively leaking into the room below almost always needs the tiles removed and the membrane replaced.
How a leaking balcony is repaired properly
- Investigate the leak with inspection and, where useful, water testing, so the fix matches the cause.
- Strip back tiles, bedding and the old membrane to the structural slab.
- Repair any concrete cancer in the slab or edge found during strip-out.
- Set correct falls to the outlet with a new screed, and fix or upgrade the drain and overflow.
- Install a new membrane suited to the balcony, with correct upturns, a door waterstop and outlet details. External above-ground membranes should comply with AS 4654.2.
- Re-tile with movement joints and reinstate or repair the balustrade.
What affects balcony repair cost?
The size of the balcony is only part of it. Cost is driven by access (a ground floor terrace versus a balcony five storeys up), how much concrete damage is found once the tiles come up, the tile selection, balustrade work, and whether the job is one balcony or a whole-building programme. Because so much is hidden under the tiles, we inspect first and give you an itemised quote so you can see what each part costs.
Balconies in strata buildings
In most strata schemes the balcony slab and membrane are common property, so the owners corporation is responsible for waterproofing repairs even though the tiles may be enjoyed by one lot. Check your by-laws and strata plan, and involve the strata manager early.
Get the balcony looked at early
Every wet season a leaking balcony stays leaking, more water reaches the steel in the slab. See our balcony repair service, or send us photos of the balcony and the ceiling below for an initial view.
