Remedial Waterproofing

Remedial waterproofing is the diagnosis and repair of existing waterproofing failures — stripping failed systems back to the substrate, repairing the base, and installing a compliant new membrane system.

Remedial waterproofing addresses waterproofing systems that have failed, aged out, or were never correctly installed in the first place. It differs fundamentally from new-build waterproofing: the diagnostic phase is critical, because the source of failure must be correctly identified before any repair is carried out. The process typically involves removing the surface finish (tiles, deck boards), exposing and assessing the substrate and any remaining membrane, carrying out any necessary substrate repairs, and then installing a new membrane system compliant with AS 3740-2021 (for internal wet areas) or AS 4654 (for external above-ground membranes). It is specialist work — misdiagnosis results in repeated failure.

Common signs of waterproofing failure include water staining below wet areas, efflorescence on tiles or grout, hollow-sounding tiles, recurring mould, and damp or musty smells in adjacent rooms.

Waterproofing failure shows itself in predictable ways. Look for: water staining or damp patches on ceilings or walls below a bathroom or balcony; efflorescence (white crystalline salt deposits) on tiles, grout, or concrete surfaces; tiles that sound hollow when tapped with a coin — this indicates water has compromised the adhesive bed; mould or mildew that returns within weeks of cleaning; musty odours in rooms adjacent to or below wet areas; lifting, cracking, or blistering of the floor or wall surface; and in severe cases, structural cracking, spalling concrete, or rust staining from corroding reinforcement. If you see any of these signs, don't wait — water damage is progressive.

In almost all cases, no — a compliant waterproofing installation to AS 3740-2021 requires the substrate to be fully exposed, and cannot be achieved over existing tiles.

Surface sealants and injection systems are sometimes marketed as 'waterproofing over tiles' solutions, but these are at best temporary remediation measures — they do not constitute a compliant membrane system under AS 3740-2021 and will not satisfy a building surveyor's inspection. For a durable result, the substrate must be exposed, assessed, and prepared correctly before the membrane is applied. The membrane must be continuous and correctly detailed at all junctions, corners, and penetrations — none of which can be achieved with tiles in place. We'll always tell you if a surface treatment is genuinely appropriate for your specific situation, but for any active water ingress, a full strip is required.

All work complies with AS 3740-2021 (Waterproofing of Domestic Wet Areas), AS 4654 for external membranes, and the National Construction Code (NCC).

The primary Australian Standard for internal wet area waterproofing is AS 3740-2021, which specifies minimum membrane coverage areas, application heights, junction detailing, and cure times. For external above-ground applications such as balconies and decks, we also reference AS 4654.1 and AS 4654.2. All our work is carried out in compliance with the applicable provisions of the National Construction Code (NCC) Volume One (Class 2–9 buildings) or Volume Two (residential), as applicable. For large commercial or strata projects, we can arrange independent third-party inspection and certification.

Quality waterproofing membranes installed correctly to AS 3740-2021 typically last 10–25 years, depending on the product type, UV exposure, substrate movement, and maintenance.

The service life of a waterproofing membrane depends on several factors: the membrane type (sheet membranes in external applications typically outlast liquid-applied systems in high-UV exposure), the quality of the original installation, the extent of substrate movement over time, and whether maintenance items like sealant joints have been renewed at appropriate intervals. Residential shower waterproofing typically lasts 10–15 years before remediation is warranted. Balcony membranes in direct sun may require inspection after 10 years. The key factor is correct installation — a high-quality product applied over a poorly prepared substrate, or with inadequate detailing at junctions, will fail prematurely regardless of its rated life.