How Do I Test If My Waterproofing Membrane Is Working Correctly?

A waterproofing membrane that's failing can cause serious and costly damage to your home — from rotting framing to mould growth and structural issues. The good news is there are a few straightforward tests you can carry out yourself, plus clear signs to watch for that tell you when it's time to bring in a licensed waterproofer.

Why Testing Your Membrane Matters

In New Zealand, waterproofing is a critical part of Building Code compliance, particularly under Clause E3 (Internal Moisture) and Clause E2 (External Moisture). Wet areas like showers, baths, laundries, and balconies must be properly waterproofed to prevent moisture from penetrating into the building structure. A membrane that isn't performing correctly can lead to hidden water damage that's expensive to fix and, in rental properties, may be relevant to landlord obligations under the Healthy Homes Standards.

Visual Inspection: Your First Step

Before doing any water testing, start with a thorough visual inspection of the membrane and its surrounding surfaces:

• Look for cracks, bubbles, blistering, or peeling in the membrane surface or the tiles/coating above it.
• Check junctions and corners — these are the most common failure points. Look for gaps, shrinkage, or separation from the wall or floor.
• Inspect grout lines for cracking or missing grout, which can allow water to bypass the membrane.
• Look for efflorescence (white chalky deposits) on tiles or walls, which can indicate water is moving through the substrate.
• Check for damp patches, staining, or mould on ceilings or walls adjacent to wet areas — these are strong indicators of membrane failure.

If you spot any of these signs, it's worth doing a flood test before assuming the worst, but also worth getting a professional opinion.

The Flood Test (Ponding Test)

The flood test (also called a ponding test) is the most reliable DIY method for checking whether a membrane is holding water. It's commonly used by waterproofing contractors and inspectors, and is referenced in good practice guides from BRANZ.

How to Carry Out a Flood Test

1. Block the drain using a rubber drain plug or a purpose-made test plug (available from plumbing suppliers or hardware stores like Bunnings or Mitre 10).
2. Fill the area with water to a depth of at least 25 mm — enough to cover the entire membrane surface, including upstands at the base of walls.
3. Mark the water level clearly with a pencil or tape on the wall.
4. Leave for 24 hours — some professionals recommend up to 48 hours for a more thorough test.
5. Check the water level after the test period. If the level has dropped noticeably (accounting for evaporation), water is escaping through the membrane.
6. Inspect below — check the ceiling or space beneath the wet area for any signs of moisture or dripping.

Important: Only carry out a flood test on areas designed to hold water (shower floors, balconies with upstands). Do not attempt this on walls or vertical surfaces.

Moisture Meter Testing

A moisture meter can be a useful tool for detecting elevated moisture levels in walls and floors around wet areas without causing damage. You can hire or purchase these from hardware stores. Readings significantly above the baseline for your wall or floor material suggest moisture is penetrating. However, moisture meters have limitations — they measure surface and near-surface moisture, not deep structural moisture — so treat results as indicative rather than definitive.

Testing Balcony and Deck Membranes

Balcony and deck waterproofing is particularly important in New Zealand given our variable climate and the history of leaky building issues. For these areas:

• Check that falls (drainage slopes) are adequate — water should not be pooling on the surface.
• Inspect flashings and junctions at walls, posts, and balustrades carefully.
• Look for any cracking in the membrane coating or exposed areas where UV degradation may have occurred.
• A flood test can be carried out on balconies with upstands, but get professional advice first if you're unsure about the structure's ability to hold the water load.

For technical guidance on external moisture management, MBIE Building Performance provides useful resources on Building Code compliance.

What to Do If the Membrane Is Failing

If your flood test or visual inspection reveals a problem:

• Don't ignore it — water damage compounds quickly and can affect structural timber, insulation, and cause mould.
• Identify the source as precisely as possible before any repair work begins.
• Document everything with photos, especially if the property is under warranty or if a builder or waterproofer may be liable.
• In wet areas, repairs will typically involve removing tiles, reapplying membrane, and retiling — this is specialist work.

When to Call a Professional

You should engage a licensed waterproofing contractor if:

• Your flood test confirms water loss and you can't identify the source.
• You find significant cracking, delamination, or structural moisture damage.
• The waterproofing is on a balcony, deck, or roof — these are higher-risk areas with more complex detailing.
• You're planning a renovation that involves wet areas — waterproofing in these areas must comply with the NZ Building Code, and depending on the scope, a building consent may be required. Always check with your local council, as some work may qualify as exempt under Schedule 1 of the Building Act, but this is not guaranteed.
• You're a landlord with obligations under the Healthy Homes Standards.

A qualified waterproofer will have the right products, tools, and knowledge of NZ standards to carry out a proper repair. You can find experienced local waterproofing professionals on tradedirectory.co.nz.

Sources & Further Reading

• BRANZ — Building Research Association of NZ
• MBIE Building Performance — NZ Building Code
• Tenancy Services — Healthy Homes Standards
• Ardex NZ — Waterproofing Systems
• Mapei NZ — Waterproofing Products
• Sika NZ — Waterproofing Solutions