Common Waterproofing issues

In Victoria (and more broadly across Australia), the most common issues with wet area waterproofing—especially in bathrooms, laundries, and ensuites—relate to non-compliance with AS 3740 (Waterproofing of domestic wet areas) and NCC Volume Two (Housing Provisions). Below are the most frequent issues observed in residential construction:

 Common Waterproofing Issues in Wet Areas (Victoria)

1. Incorrect Fall to Floor Waste

• NCC Reference: NCC 2019 Volume Two Clause 10.2.12

• Issue: Floor tiles or screed not sloped properly toward the waste, causing ponding or water flow outside the wet area.

• Requirement: Min. fall of 1:100 in showers, 1:80 in other wet area floors.

2. Missing or Improper Waterstops

• NCC Reference: Clause 10.2.18

• Issue: No waterstop angle at door thresholds or at the junction of wet/dry areas, allowing water egress into adjacent rooms.

• Fix: Install aluminum or PVC angle waterstops at the slab/screed junction, extending to full membrane height.

3. Membrane Termination Issues

• Membrane not returned up walls far enough or not integrated properly behind wall tiles, especially behind vanity units or niches.

• AS 3740 requires vertical upturns of at least:

  • 150 mm at walls

  • 25 mm above the hob or threshold

  • 1800 mm in shower walls

4. No Bond Breaker or Movement Joint Treatment

• Flexible membranes require bond breakers at wall-floor junctions and around penetrations to prevent cracking or detachment due to movement.

• Issue: Membrane applied directly into sharp corners without a bond breaker.

5. Membrane Not Applied to Entire Required Areas

• For example:

  • Not continuing membrane behind or under bath edges

  • Not waterproofing up behind wall-hung vanities or shower recesses

6. Incorrect Membrane Thickness / Number of Coats

• Manufacturer instructions often require 2 or more coats and a minimum DFT (dry film thickness), but contractors sometimes skip or apply thinly.

7. Poor Surface Preparation

• Dust, laitance, or moisture present on substrate before membrane application.

• Inadequate priming can lead to delamination.

8. Incompatible Tiling Materials or Adhesives

• Adhesives not compatible with the membrane or applied before membrane has cured.

9. No Compliance Certificate 

• Waterproofing works in Victoria must be certified by a registered waterproofing contractor, who provides a Form 126 certificate for compliance.

• Some builders skip this step or use unregistered trades.

10. Penetrations Not Properly Sealed

• Floor wastes, tap spindles, shower mixers, and wall penetrations not sealed with grommets or membrane detailing.

 Useful Guidelines

• Australian Standards: AS 3740:2021

• Building Code of Australia (NCC Volume Two)

• Victorian Building Authority (VBA) Practitioner Resources

What VIC Law Requires for Bathroom Waterproofing

•  Waterproofing must meet Australian Standard AS 3740
•  Only VBA-registered practitioners may carry out waterproofing work
•  A certificate of compliance must be issued and retained
•  Building permits may be required for major works or structural changes

Conclusion: Protect Your Home with Professional Waterproofing

Waterproofing might be hidden behind tiles and finishes, but when done incorrectly, the consequences are far from invisible—ranging from mould, structural damage, to costly repairs. The issues outlined above are all too common in Victorian homes, especially when shortcuts are taken or unlicensed contractors are involved.

At Alert Construction, we ensure every waterproofing job complies with AS 3740 and the National Construction Code, backed by certified materials and licensed practitioners. Don’t risk your investment by leaving this critical task to chance.

Choose peace of mind—work with a fully licensed, registered builder and waterproofing expert.

 Contact us today for a professional assessment or quote on your wet area renovation or waterproofing repair. You can also find our bathroom renovation packages.