The waterproofing membrane is the single most critical component of a balcony. When it fails, water penetrates the slab and travels into the structure, corroding steel reinforcement, saturating screeds, and damaging internal ceilings and finishes below. In most cases, membrane failure isn't sudden — it develops gradually through UV degradation, movement at joints, poor original installation, or physical damage from tile work above. By the time a leak is visible internally, significant damage has often already occurred.

Atomic Projects replaces balcony waterproofing membranes in full compliance with AS 4654.2 (Waterproofing Membranes for External Above-Ground Use) and the ABCB Housing Provisions, integrating all associated works — screed, drainage, and tiling — under a single contract to eliminate interface risk between trades.

How We Replace Balcony Waterproofing Membranes

• Pre-Works Investigation: Before any tiles or screed are removed, we conduct a leak investigation and water testing to confirm the membrane is the primary failure point and identify any additional defects — slab spalling, drain issues, or threshold failures — that must be addressed in the same scope.
• Full Strip & Substrate Preparation: Existing tiles, adhesive, screed, and failed membrane are fully removed to expose the concrete slab. The slab surface is ground or scarified to remove all residual adhesive and to achieve the bond profile required by the new membrane system.
• Slab Repairs: Any concrete spalling, cracking, or contaminated substrate identified during strip is repaired before membrane application. New membranes applied over a compromised substrate will fail prematurely.
• Membrane Application: A new, fully-bonded waterproofing membrane is applied as a seamless, continuous layer over the slab, turned up all perimeter upstands to a minimum 100mm above finished floor level, taken through all penetrations, and integrated with drain flanges. System selection (sheet-applied, liquid-applied, or hybrid) is specified to the exposure category and expected movement of each application.
• Flood Testing: Before any screed or tiles are reinstated, the completed membrane is flood-tested for a minimum of 24 hours to confirm watertightness. No works proceed over a membrane that hasn't passed this test.
• Screed, Falls & Tiling Reinstatement: After successful flood test, screed and fall correction are completed before tile reinstatement, restoring the balcony to full use.

Frequently Asked Questions

How do I know the waterproofing membrane has failed rather than another component?

The only reliable way to determine this is through systematic water testing and investigation. We commonly find that leaks attributed to the membrane are actually caused by failed drain flanges, cracked screed joints at the threshold, or breached upstands at the door frame. A proper investigation before demolition prevents stripping a membrane that may still be functional.

How long should a properly installed balcony waterproofing membrane last?

A correctly specified and installed membrane, with appropriate screed protection and tiling above, should achieve a service life of 20–25 years. The critical factors are correct detail treatment at upstands, drains, and penetrations, and proper adhesion to the substrate. Most premature failures occur at these transition points, not in the field of the membrane.

What is the NCC requirement for waterproofing upstands?

The NCC requires waterproofing to be turned up to a minimum height of 100mm above the finished floor level at all vertical junctions, doorways, and penetrations. This upstand requirement is one of the most frequently violated details in existing residential buildings and is a primary cause of threshold leaks.

Can the work be done in stages across a building?

Yes. For multi-storey strata buildings, Atomic Projects typically works floor-by-floor or in building quadrants, staging the program to keep disruption to individual lots to a minimum while maximising site efficiency. Each balcony is typically out of service for 10–14 working days from strip to tiled-and-cured.

Will Atomic Projects manage the full scope from investigation to finished tiling?

Yes. This is our standard approach. Managing the full scope — investigation, slab repair, membrane, screed, drains, and tiles — under a single contract removes the interface risk between separate waterproofing and tiling contractors, which is where defects most commonly recur.

Balcony waterproofing replacement is one of the most consequential remedial works in a strata building — done correctly, it protects the structure for 20+ years; done poorly, it fails within a few years and causes further damage. Atomic Projects is a Class 2 Registered Builder with over 10 years of experience in balcony waterproofing across Sydney's residential and commercial building stock. Contact us to arrange a scope assessment and proposal for your building.