Waterproofing Failures in Strata Buildings: Causes, Risks & Solutions

On a wet Tuesday in Sydney, a committee chair rang us about a “small stain” on a bedroom ceiling. By the time we arrived, the stain had turned into peeling paint, swollen skirtings and a musty odour drifting down the corridor. The source? A tired balcony membrane two floors up, letting water track through the slab. One failure, three lots affected, and an unhappy insurance broker asking for more detail than anyone had handy.

Stories like this are common across Sydney’s strata stock, particularly in older brick walk-ups and 80s–90s apartment blocks that have seen their fair share of storms, summer heat and movement. When waterproofing fails, it rarely announces itself. It creeps: a hairline crack here, a soft patch there, then damp patches that seem to move around after each downpour. Left alone, it becomes expensive very quickly.

Balconies, bathrooms, rooftops, and podiums do the heavy lifting in strata waterproofing. They cop with foot traffic, UV, cleaning chemicals, planters, furniture legs, and the odd DIY alteration. Over time, several things chip away at the system:

• Shortcuts at build time. Membranes need the right falls, coverage, thickness, and curing. If a builder rushed the job or tiled too soon, the countdown to failure started on day one.
• Movement. Sydney’s temperature swings, slab shrinkage, and normal settlement open up joints and corners. Even a quality membrane will suffer if expansion joints are missing or bridged.
• Drainage that doesn’t keep up. Blocked outlets, planters sitting over trays, or balcony doors without proper thresholds force water to sit where it shouldn’t, and it always finds a path.
• Aging and UV. Membranes, sealants, and grouts have a service life. Ten years can be kind; twenty, less so, especially on coastal sites where salt accelerates corrosion beneath the surface.
• Well-meaning DIY. Screws through tiles for privacy screens, regrouting without addressing falls, or “waterproof” paints slapped over hairline cracks… they mask the issue, not fix it.

Bathrooms fail for similar reasons. A cracked hob, a shower recess with poor falls, or a membrane that never wrapped correctly up the wall can wick water into the substrate. You won’t see it at first. Your skirting boards will.

Leaks don’t respect lot boundaries. Moisture migrates along reinforcement, finds conduits, stains the ceiling below, and sets up mould growth in the least ventilated corner of the bedroom. If you’re unlucky, you’ll also invite concrete spalling (concrete cancer) as steel reinforcement corrodes and expands, blowing the concrete cover. What began as a small balcony leak becomes a façade repair and a difficult conversation at the AGM.

There’s also the paperwork. Insurers generally cover resulting damage, not the underlying defect or gradual deterioration. By the time a claim is lodged, assessors want evidence: reports, photos, maintenance logs, and proof that the committee acted promptly. Delay can mean more out-of-pocket spend for owners.

A quick re-silicone around a balcony door feels productive, but it rarely addresses the cause. A thorough diagnosis usually looks like this:

1. Visual inspection with context. We look at falls, door thresholds, terminations, penetrations, and we check adjacent lots. Water paths are rarely vertical and rarely obvious.
2. Moisture mapping and leak testing. Non-destructive testing shows the spread; controlled water testing confirms points of entry. On complex jobs, we coordinate with engineers or use dye tests.
3. Targeted opening-up. Small destructive probes tell us exactly what’s under the tiles: membrane type and condition, screed, substrate, and whether reinforcement is already corroding.

With the picture clear, you can choose between a stop-gap (to stabilise an area or buy time for a program of works) and a proper remediation (strip, rectify, rebuild).

There’s no single “magic paint” for failed waterproofing. A durable repair is a sequence done in the right order:

• Strip back to a sound substrate. Tiles, screed, and contaminated materials come out, so we’re working on honest concrete.
• Rectify the structure and falls. We repair cracks, reinstate cover if there’s spalling, and correct falls to drains so water leaves the surface instead of lingering.
• Choose the right membrane for the location. Trafficable areas, planter boxes, and bathrooms all demand different systems (liquid-applied, sheet, or hybrid). Compatibility with adhesives and finishes matters.
• Detail the edges and penetrations. Corners, balustrade posts, door thresholds, outlets—these are the failure points. We reinforce them, not just roll over them.
• Re-tile and seal properly. Flexible adhesives, movement joints where the standards expect them, and sealants with the right UV rating.
• Prove it. Where appropriate, we pressure test or water test under supervision and document the result for the committee’s records.

If leaks have already started concrete cancer or damaged facades, we integrate remedial concrete and facade repairs into the same programme so you don’t fix one problem and leave the other brewing.

Committees don’t like surprises. A sensible approach is to stage the work:

Stage 1: Investigation & reporting. Clear scope, photos, and drawings. This helps with owner communication and, if needed, insurance discussions.

Stage 2: High-risk areas first. Balconies or roofs affecting multiple lots get priority. Bathrooms with visible mould or swollen joinery follow.

Stage 3: Programmed remediation. Group similar works to minimise access costs, scaffolding, and defect liability headaches.

We’re always upfront about what’s urgent versus what can be scheduled, and we provide options so the committee can plan cash flow with eyes open.

Ardent Construction is a Sydney remedial builder that spends most days in live strata environments coordinating with managers, engineers, residents, and neighbours. The work is as much about clear communication and safe access as it is about the technical fix. We:

• Investigate properly and put findings in plain English for committees
• Stage works to reduce disruption (week-by-week programmes and notices residents actually read)
• Handle balcony, bathroom, and roof membrane replacements, plus the concrete and facade repairs that often come with them
• Leave you with photos, test results, and a maintenance plan so future committees aren’t guessing

Explore related services:

• Strata remedial works
• Remedial building & waterproofing
• Concrete cancer repairs
• Heritage facades (for older blocks)