What are the first signs of a bad waterproofing job?

The earliest signs include: bubbles or blisters in the membrane surface (indicating poor adhesion or trapped moisture), visible wrinkles or fish-mouths at seams, inadequate overlap at membrane joints, membrane pulling away from upstands or wall junctions, and standing water (ponding) that doesn't drain within 24 hours of rain. Any of these warrant immediate professional inspection.

Should I get a waterproofing inspection before buying a house?

Absolutely. A pre-purchase waterproofing inspection is one of the most valuable investments you can make when buying an Auckland property with flat roofs or decks. We regularly conduct these inspections and provide detailed reports on the condition, remaining life and any remediation needed for existing waterproofing systems.

Can a bad waterproofing job be fixed without full replacement?

It depends on the extent of the problems. Minor issues like isolated seam failures can sometimes be repaired. However, if the fundamental installation was substandard — wrong system for the application, inadequate preparation, incorrect falls — targeted repairs are unlikely to provide a lasting solution. A full assessment is needed to determine the most cost-effective approach.

How do I verify a waterproofing contractor's credentials?

Check their LBP status on the public register at lbp.building.govt.nz. Ask for their LBP number and verify the endorsements match the work (Roofing R4/R5 for membrane work). Check for manufacturer approved applicator status. Request references from recent projects. A legitimate contractor will have no issue providing all of this.

How to Spot a Bad Waterproofing Job Before It's Too Late

Not all waterproofing work is created equal. In Auckland, we regularly get called to inspect and remediate waterproofing installations that have failed prematurely — often within just 2–5 years of installation. In many cases, the warning signs were visible from the start, but the homeowner didn't know what to look for.

This guide will help you identify the red flags of substandard waterproofing work — whether you're checking a recent installation on your own property, inspecting a property before purchase, or evaluating a contractor\'s quote.

Red Flag #1: No LBP Licensing

This is the single biggest warning sign. Waterproofing membrane installation is restricted building work under the Building Act 2004. If the person installing your membrane is not a Licensed Building Practitioner, the work is being done illegally. This isn't a technicality — it means there's no regulatory oversight, no professional accountability, and no recourse through the Building Practitioners Board if things go wrong.

Always ask for the contractor's LBP number and verify it on the MBIE public register. Check that their endorsements include Roofing (R4 and/or R5), which covers membrane roofing and waterproofing work.

Red Flag #2: Wrong Membrane System for the Application

Every waterproofing application has specific requirements, and not every membrane system is suitable for every use. Common mismatches we see include:

Using Butynol on high-UV-exposure roofs where TPO would be more appropriate
Using non-trafficable membranes on decks that will have foot traffic
Using adhesive-seam membranes in high-movement areas where heat-welded seams are needed
Applying exterior-grade membranes on internal tanking applications

Red Flag #3: Inadequate Surface Preparation

The membrane is only as good as the substrate it's applied to. Before any membrane is installed, the substrate should be clean, dry, free of debris, properly primed, and have the correct drainage falls. If the installer is laying membrane on top of a dirty, wet or uneven surface, the installation will fail.

Good practice includes checking the plywood for rot or delamination, ensuring all screw heads are flush, rounding any sharp edges that could puncture the membrane, and applying the manufacturer's specified primer.

Red Flag #4: Poor Seam Quality

Seams are where most waterproofing failures originate. On heat-welded systems (TPO, torch-on), look for consistent weld width, no burn-through marks, and no areas where the seam can be pulled apart. On adhesive systems (Butynol), check that laps are flat, fully bonded and free of wrinkles or fish-mouths.

Red Flag #5: Inadequate Detailing at Critical Points

The “flat” areas of a membrane are rarely where leaks occur — it's the details that fail. Critical points include upstands where the membrane meets walls, penetrations for pipes and drains, internal and external corners, changes in direction, and scupper outlets. Every one of these points needs meticulous detailing.

Red Flag #6: No Documentation

A professional waterproofing installation should produce documentation including: a detailed scope of works, the BRANZ appraisal for the membrane system, manufacturer's installation certificate, a warranty for both materials and workmanship, and photos of the completed installation including all concealed details. If none of this is offered, question the quality of the work.

Red Flag #7: Suspiciously Low Pricing

Waterproofing is technical work that requires quality materials, specialist equipment and considerable expertise. If a quote is significantly lower than others, it usually means corners are being cut — cheaper materials, less preparation, fewer overlaps, no primer, rushed installation. The cost of remediating a failed waterproofing job is typically 2–4 times the cost of doing it right the first time.

What Good Waterproofing Looks Like

Membrane lies flat with no wrinkles, bubbles or fish-mouths

All seams are consistent, fully bonded and cannot be peeled apart

Upstands are neat, fully adhered and extend minimum 75mm above finished surface

Drainage falls are visible — water runs to the outlets, not to dead spots

All penetrations have proper collar details

Edge trims and drip edges are installed correctly

The membrane surface is clean and free of foot traffic damage

Documentation is provided without having to ask

When to Get a Second Opinion

If you have any doubts about the quality of waterproofing work on your property — whether it's a recent installation or a pre-purchase inspection — invest in an independent assessment from a different LBP-licensed waterproofing specialist. The cost of an inspection ($300–$600) is negligible compared to the cost of remediating a failed installation ($5,000–$50,000+).

Contact us for an honest, independent assessment of your waterproofing. We'll tell you what's good, what's not, and what needs attention — whether we did the work or not.