C13A Waterproofing Design Checklist: Get It Right Before the Membrane Goes On

Introduction: Why Waterproofing Design Matters More Than You Think

If you’ve ever spoken to someone who's had a leaking bathroom, you’ve probably heard words like “nightmare,” “expensive,” or “builder wouldn't return my calls.” And they’re not exaggerating.

Waterproofing defects are among the most common and costly problems in new homes. Worse, they usually don't show up until months or years after handover, when fixing them means ripping out perfectly good tiles, cabinetry and walls. Most of them were entirely preventable.

That's why we created the C13A Waterproofing Design Checklist. It helps homeowners, builders and waterproofers make the right choices before a single drop of product is applied.

In this post I'll walk you through what the checklist covers, how it works, and why using it could save you thousands of dollars and a lot of finger-pointing down the track. Even if you're only trying to understand what your builder should be doing, this will help.

What is the C13A Waterproofing Design Checklist?

The C13A Waterproofing Design Checklist is a structured guide for planning and documenting the waterproofing system for a new home, before the work begins.

It's a design tool, not an installation checklist. It makes sure the right products are selected, the surfaces are properly prepared, and every part of the system is compatible with the rest. That distinction matters.

Too often in residential construction, particularly in volume builder homes, waterproofing is treated as a box-ticking exercise. A bond breaker goes in (maybe), two coats of membrane get rolled on like paint, and everyone assumes the job's done.

But what if the substrate (the surface being waterproofed) wasn't dry enough, or it was too hot, or the humidity was outside the product's limits? What if the primer wasn't compatible, the connector sealant was the wrong brand, the membrane couldn't handle the floor's movement, or the cracks weren't prepped? Then you've just installed a future leak.

The C13A checklist makes you ask the right questions before waterproofing starts:

• What are the site conditions like? Is the substrate porous? Damp? Flexible?
• Have we chosen a membrane that suits those conditions?
• Are the connector sealants compatible with the membrane?
• Have we communicated the system properly to follow-on trades like tilers or cabinet installers?

C13A - Waterproofing Design Checklist

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Last updated 28 Oct 2026 · Revision 3 · Free updates for life

Checklist Type: Minor

Form Factor: Fillable, print-ready PDF (A4, 23 pages)

When to use: Design stage: before waterproofing starts, while products and details can still change

A 59-point waterproofing design checklist. Settle shower types, set-downs, falls and one compatible set of products on paper, before anyone picks up a brush.

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Why Design Matters Before You Waterproof

Most people think of waterproofing as the stuff that gets rolled on just before the tiles go down. That's one part of it, but waterproofing is really a system, not a single product, and like any system it has to be designed properly to work.

A typical waterproofing setup might include:

• A prepared substrate (like fibre cement sheeting or concrete),
• A compatible primer,
• A bond breaker at movement joints,
• A membrane (liquid or sheet),
• A compatible sealant at penetrations and junctions,
• And a finish, like tiling, laid with a flexible adhesive.

If even one of these parts is incompatible with the others, or doesn't suit the site conditions, you've got a failure waiting to happen.

So where do most jobs go wrong?

1. No compatibility check.
   Products are mixed and matched from different manufacturers, without checking if they actually work together. The result? Membranes peel, tiles de-bond, or the whole system cracks under stress.
2. Wrong membrane for the job.
   For example, using a membrane that’s not UV-stable on an external balcony. Or applying a membrane with low flexibility on a suspended timber floor that moves over time.
3. Poor surface preparation.
   If the substrate is wet, contaminated, or too porous — the membrane won’t bond. And no, more coats won’t fix that.
4. No allowance for curing time or site conditions.
   Membranes need to cure in certain conditions — temperature, humidity, airflow — and if that’s ignored, you’re back to square one.
5. No communication with other trades.
   A tiler, plumber, or cabinet installer may cut into or damage waterproofing layers if they don’t know what’s there or why it matters.
6. Incorrect application.
   One of the most common, and most preventable, mistakes. Not reading or following the Product Data Sheet (PDS) and Technical Data Sheet (TDS) leads to poor installation. That includes not reaching the correct Wet Film Thickness (WFT), the thickness while wet, or Dry Film Thickness (DFT), the thickness once cured, and not checking them during application. Just slapping on more product doesn't guarantee performance and can even cause failures.

It takes a lot of liquid membrane to reach the minimum WFT, often around 0.75 mm (750 microns) per coat. Check the data sheet for your product. You really have to lay it on thick. Neat, thin rolled coats on a wall usually won't meet the manufacturer's WFT requirement.

And here’s the part homeowners often don’t hear:

Once tiles are laid and the bathroom is fitted out, you can't see a waterproofing failure until the damage is done: mouldy walls, swollen cabinetry, leaking balconies or structural rot. Fixing it means demolition, disruption and dollars.

Designing the system properly, with a checklist like C13A, is how you avoid that mess. It forces deliberate decisions about materials, curing time, compatibility and installation methods.

Breaking Down the Checklist, Section by Section

Here's what the C13A checklist covers and why each part matters.

Section 1: General Considerations (Walls and Floors)

This section covers the materials you're waterproofing over. It looks simple, but it's where a lot of jobs quietly go off the rails. The checklist has you confirm what wall and floor substrates are being used, and whether they suit wet areas, before any waterproofing starts.

Walls: Don’t Stick Waterproofing to the Wrong Substrate

• Only use wet area-rated sheeting. Fibre cement (FC) sheeting must be rated for wet areas and be at least 6mm thick for standard tiling, or 9mm if your tiles weigh over 32kg/m².
• Plasterboard? Handle with care. Yes, you can use water-resistant plasterboard in wet areas, but only when installed correctly (10mm min. thickness, 600mm max. stud spacing, and mechanical fixings). Never use it behind heavy tiles or where direct water exposure is likely.
• Direct-fixing to masonry? Big no. Sheeting must be battened out to allow airflow — direct-fixing traps moisture and encourages mould or de-lamination.
• Sheet fixing must be spot on. The checklist outlines specific screw centres, joint clearances, and even cautions against using stud adhesive, which can interfere with movement and bonding.

Floors: Don’t Just Slap Membranes on Timber

• All timber floors must be waterproofed. AS3740:2021 is clear on this — no exceptions.
• Particleboard? You can use it internally, but it must be over-sheeted with fibre cement before waterproofing. For external areas, it’s not allowed at all (per AS4654.2).
• Sheet layout and bonding matter. You’ll need to consider whether sheets should be laid in stacked or staggered bonds depending on the type of membrane (bonded or unbonded) and system used.
• Deflection gaps and adhesive use. Floor sheets should be gapped 3mm for compressive movement and glued down with a notched trowel, using the specified adhesive, not whatever glue is handy.
• Mechanical fixings must meet spec. Fastener spacing, edge distance, and layout all affect how the sheeting moves under load — which directly affects how long your membrane lasts.

Our companion C13B Waterproofing Installation Checklist covers waterproofing installation quality management.

Section 2: Surface Conditions

Before any membrane goes down, the first question isn't what you're using. It's what you're applying it to. This section is about the condition of the surface (the substrate) being waterproofed. Skipping it is like painting over a damp, flaking wall and expecting it to last.

Porous vs Non-Porous Substrates

• Porous substrates (like concrete, screeds, fibre cement sheeting) absorb moisture. These usually need priming before membrane application.
• Non-porous substrates (like metals or some dense tiles) don’t absorb anything — and require specific primers to get a proper bond.

The checklist makes you identify (some would say "pushes you outside your comfort zone" 😉) which surfaces are porous or non-porous, because using the wrong primer, or skipping it, leads to de-lamination (the membrane lifting away) and total membrane failure.

Moisture Content

This one’s non-negotiable.
Before waterproofing, substrates must be dry enough to allow the membrane to adhere and cure correctly. That means:

• Using a moisture meter to test screeds and concrete.
• Not just going by feel or colour — moisture can be hidden below the surface.
• Respecting curing times (e.g., 28 days for concrete, 7+ days for screeds unless using damp-tolerant primers).

If your builder or waterproofer can’t show you a moisture reading, that’s a red flag.

Moisture and temperature readings are a big deal when it comes to waterproofing. Yet it's rare to see trades using humidity gauges or surface temperature probes before starting work. Not saying all waterproofing trades — just most don't do it.

Contamination & Cleanliness

• Is the surface clean?
• Has it been exposed to dust, oil, release agents, or paint overspray?
• If so, it may need mechanical or chemical treatment first — otherwise, the membrane won’t bond.

You wouldn’t put stickers on a greasy car — so why would you roll on a membrane over a dirty slab?

Condensation & Underside Moisture

In some builds, especially multi-storey homes or ones with tight roof spaces, you can get condensation under roof decks or between floors.

This moisture from the underside can ruin a waterproofing job before it even starts. The checklist includes a reminder to check for signs of condensation and account for it in the system design (e.g., using a negative pressure membrane or better ventilation strategies).

Service Conditions & Movement

The checklist prompts you to think about:

• Whether the area will see heavy foot traffic (requiring an abrasion-resistant membrane),
• If there are flexible or rigid substrates,
• And whether you need root resistance (for planter boxes, green roofs, etc.).

It also asks you to confirm the flexibility class of the membrane — Class I, II, or III — which determines how much movement it can tolerate. (More on that in the next section.)

Section 3: Membrane Selection

Now you know what you're sticking the membrane to, it's time to choose which membrane. They're not all the same.

This part of the checklist matches the membrane properties to the real conditions on your build. It's not about what's on special at the trade counter. It's about the membrane that will last with the surface and conditions you've actually got.

1. Rigid or Flexible?

• Rigid membranes can handle hard, stable surfaces with minimal movement.
• Flexible membranes are for substrates that move — like timber floors, balconies, or suspended slabs.

Flexible membranes are more forgiving, but they also require proper installation to work effectively. Think about movement joints, foot traffic, temperature fluctuations, and what's underneath.

2. What’s the Flexibility Class?

This comes down to the expected movement in the substrate and the bond breaker size required. Membranes are classified under AS4858 into:

• Class I: Low flexibility (10–60% elongation)
• Class II: Medium flexibility (60–299% elongation)
• Class III: High flexibility (>300% elongation)

More movement = higher flexibility class = smaller bond breaker. If you don’t match the membrane to the expected movement, it’ll crack — simple as that.

3. Abrasion Resistance

If you’re waterproofing a trafficable area (like a rooftop deck or balcony), you’ll need a membrane that can stand up to foot traffic, furniture, and weather exposure. Not all membranes are designed to take a beating.

If you use a bathroom-only membrane outside or under pavers, it’s going to fail. Maybe not today, but definitely when it matters most — usually after handover.

4. Root Resistance

If you’re dealing with planter boxes or garden rooftops, your membrane needs to resist root penetration — because plants don’t care about your warranty. This usually means specifying a membrane designed for landscaping applications.

Section 4: Curing Time and Conditions

You've chosen the right membrane. The surface is clean, dry and ready. You start applying it... and then it rains. Or it's 40°C in the sun. Or there's no airflow and the humidity is at 90%. That membrane might never cure properly, and if it doesn't cure, it doesn't work.

This section covers something many builders and waterproofers don't pay enough attention to: the conditions the membrane needs to set and perform.

Wet Film Thickness (WFT) and Dry Film Thickness (DFT)

Every liquid membrane has a target thickness that must be achieved:

• WFT: The thickness while the membrane is still wet.
• DFT: The final thickness after it has dried and cured.

If you apply it too thin, it won’t perform.
If you apply it too thick, it may not cure properly — or it could trap moisture, leading to bubbling, blistering, or de-bonding.

👉 This is why it’s essential to read the Product Data Sheet (PDS) and check your membrane thickness as you apply it. Don’t guess. Use a wet film gauge. Check multiple points. Document it if you want to avoid arguments later.

Curing Conditions Matter

The checklist prompts you to consider:

• Airflow: Is the space ventilated enough for the membrane to off-gas and cure?
• Relative humidity: High humidity can delay or block curing altogether.
• Ambient temperature: Most membranes have a safe application range (usually 10°C–35°C). Outside of that, curing slows, fails, or goes sideways entirely.
• Surface temperature: The surface might be hotter or cooler than the air — especially on roofs or balconies. Membranes may flash dry or not dry at all.

Why this is a big deal:
If you don’t control the curing conditions — or worse, ignore them — you might think the membrane is fine… until tiling starts and the surface bubbles, cracks, or detaches. At that point, it’s already too late.

"She'll be right" doesn't work here. Curing is chemistry. It's not about slapping on two coats with a heavy-nap roller until it "looks about right". The membrane must meet the WFT and DFT on the data sheet, or it won't perform, and you'll be paying for a bathroom rebuild.

Section 5: Installation Factors

Some waterproofing products are easy to install. Others... not so much. This part of the checklist makes you think about how the waterproofing will actually get done on site, by real people, in real conditions, with limited time and tools. If a system is too hard to apply or needs lab-like conditions, it probably won't get installed the way the brochure says.

Ease of Use

• Is the membrane a one-part product, or do you need to mix two parts together on-site?
  • Have you got multiple buckets available to ensure consistent product mix batches?
• How easy is it to spread or roll? Can it be sprayed?
• Does it need specialist tools or trades?
• Is the working time short in hot conditions?

The easier a product is to install, the more likely it’ll be applied properly — especially on busy sites where time is tight and trades are stacked.

Environmental Impact & Safety

• Does it contain solvents or require hazardous waste disposal?
• Is the smell a problem in occupied buildings?
• Does it require special storage conditions or ventilation?

Some membranes are classified as hazardous and may require air extraction, flammable material handling, or additional PPE. These details are all found in the SDS (Safety Data Sheet) and must be reviewed before use.

Toxicity and Ventilation Needs

• Is PPE like respirators or gloves required?
• Will application release VOC fumes that need to be managed?
• Does the site need ventilation fans or limited access during application?

These aren’t just questions for the installer — they affect how the whole site is scheduled and who can work nearby. That’s why this section of the checklist exists: to plan ahead, not troubleshoot on the day.

Sections 6 and 7: PPE and Safety

These sections are mostly for the builder and the waterproofer, but they matter to you because unsafe work is rushed work. Many waterproofing systems involve hazardous chemicals, solvents and dust (including silica from grinding screeds) that put installers and other people on site at risk.

The checklist prompts the team to confirm, before work starts:

• The right PPE: respirators (such as P2 or fit-tested masks), gloves, eye protection and dust extraction.
• Ventilation for products that give off fumes, and whether the area should be isolated during application.
• Whether a Safe Work Method Statement (SWMS) is needed. It's legally required for hazardous materials and high-risk work such as roofs, balconies and confined spaces.
• Safe storage: dry, cool, out of the sun, away from flammables, and secure. Two-part products can cure in the bucket or heat up if stored badly.

QMP and ITPs: Quality and Safety Go Together

The checklist encourages builders to include waterproofing in their:

• The Quality Management Plan (QMP)
• The Inspection and Test Plan (ITP)

Having an ITP means:

• The work is signed off at key stages (e.g. substrate inspection, membrane application, curing, flood testing)
• Defects are caught early — before they’re tiled over
• There's a paper trail for compliance and warranty support. Without a documented compatibility chain, site records and readings, you have no manufacturer's product warranty. If the system fails and you can't show how you met the manufacturer's requirements, the failure is on you.

Section 8: Application

Now we're into the nuts and bolts of applying the system. This section covers what's involved, what tools and products are needed, and how to make sure the system goes on the right way, not the easy way. It's not about telling your waterproofer how to do their job. It's about making sure the method matches the design and nobody takes shortcuts that fail under the tiles.

One-Part vs Two-Part Products

• One-part membranes come pre-mixed, ready to apply, and are generally easier to manage on site. A typical example is a pre-mixed liquid membrane straight from the pail: stir and apply.
• Two-part systems require mixing a resin and hardener, and are often more durable, but they have a limited pot life once combined. WPA200 is a good example (mix part A and B, rest, mix again, apply).

The checklist asks you to note this, because once a two-part product is mixed, the clock is ticking. If follow-on trades don’t know this, or if it’s mixed too early, the material can harden before it’s applied — and that’s wasted product and money.

Mixing Requirements

Some membranes require specific:

• Mixing ratios (by weight or volume)
• Tools (e.g. low-speed drills with mixing paddles)
• Clean, dry buckets and controlled batch sizes

Improperly mixed membrane = improperly cured membrane. This section ensures someone has actually read the PDS and knows how to mix it correctly.

Reinforcement and Bond Breakers

Depending on the membrane and substrate movement, you might need:

• Reinforcement fabric in wall-floor junctions
• Bond breakers to allow for movement
• Fillets at corners to prevent sharp internal angles

The checklist forces clarity on:

• Where reinforcement is needed
• What size bond breaker is required (depends on flexibility class: Class 1, 2 or 3)
• Whether you're using sealant, bandage, or a release tape system

Miss any of these, and movement cracks the membrane — end of story.

Cleanup, Compatibility, and Costs

• Type of cleanup: Some systems need solvent clean-up, others are water-based. This affects PPE and disposal planning.
• Compatibility with adhesives and finishes: Tilers need to know what they’re sticking to. Not all adhesives bond to all membranes.
• Cost: Choosing the cheapest membrane but needing four coats to achieve DFT isn’t cost-effective. The checklist helps identify total system cost, not just product cost.

Screed Positioning and Application Sequence

• Is the membrane going above or below the screed?
• Are falls already formed in the slab or screed?
• Are penetrations sealed before the screed goes down?

Getting the sequence wrong, such as waterproofing before the waste locations are set or after the cabinet bases are fixed, can ruin the system and force expensive rework. We highly recommend installing the membrane above the screed. Unless the substrate below has falls to the waste, a membrane under the screed sits in trapped moisture, which can chemically attack and break down the membrane.

Full Immersion or Damp Tolerance

Some areas (like planter boxes, bath hobs, or balconies) are exposed to water for long periods. If your membrane isn’t rated for full immersion or rising damp, it’ll blister or fail.

This section confirms:

• If immersion is part of the design
• Whether the membrane is rated for it

Section 9: Compatibility Chain

This section sounds technical, but it's one of the most important and most overlooked parts of waterproofing design.

The compatibility chain means every product in the system works together: primer, membrane, sealants, adhesives, tile finishes, even cleaning products. They all need to be chemically and mechanically compatible. If one product breaks the chain, the whole system can fail.

We're not picking on plumbers, but cutting into the waterproofing around tap sets and resealing it with roofing or gutter silicone breaks the chain. It's usually not malicious. Nobody told them which connector sealant to use. A quick chat between the builder and the trades prevents it. We've also heard of waterproofers swapping the specified sealant for a cheaper generic one to save a few bucks. If there's a leak and the manufacturer's tech rep spots the wrong sealant, that $30 saving turns into a full bathroom rip-out with no warranty support.

What's in the Chain?

The compatibility chain includes:

• Substrate
• Substrate primer
• Junction/connector sealant
• Bond breaker
• Membrane Primer
• Waterproofing membrane
• Surface Finish Primer
• Surface Finish Adhesive
• Surface Finish Fillers (grouts, adhesives, sealants)

Each one has to be designed to work with the others, and ideally, they should all come from the same manufacturer — or at least be confirmed by the manufacturer as compatible.

Why? Because when things go wrong, most manufacturers will void warranties if their product was used with another brand’s system — even if you followed all other directions.

The “Frankenstein System”

We’ve seen it before:

• Primer from Brand A,
• Membrane from Brand B (because it was cheaper),
• Silicone from Brand C (because the plumber brought it),
• And grout from wherever the tiler shops.

No one has cross-checked anything. No one asked for a TDS. No one told anyone else anything, so everyone assumed what they had was fine. And no one realises Brand B's membrane won't bond to Brand A's primer until water is pooling behind the tiles.

Result? A waterproofing failure that’s not covered by any warranty. Everyone points fingers. The owner pays.

🔗 The rule is simple: if it touches another part of the system, it must be compatible.

Manufacturer PDS & TDS: Your Best Friend

The checklist reminds you to:

• Get the Product Data Sheets (PDS) and Technical Data Sheets (TDS) for each product
• Confirm compatibility in writing or published documentation
• Choose a single manufacturer system where possible

That way, if something does go wrong, you’re backed by documentation — and not caught in a blame game.

Sections 10 to 14: Applying the Compatibility Chain Across All Areas

Sections 10 to 14 apply the same process (assess, design, match, document) to three waterproofing zones: internal wet areas, external above-ground areas and below-ground areas. Each one needs different products and performance.

🛁 Internal Areas (Bathrooms, Laundries, Ensuites)

This is the most common waterproofing zone — and often where the most shortcuts happen. Internal wet areas need:

• A membrane compatible with tile adhesives and sealants.
• Attention to bond breakers at wall/floor junctions.
• Correct primer and sheeting systems behind it all (FC sheeting, wet area plasterboard, etc.).
• Sufficient moisture testing and ventilation to ensure curing.

💡 Tip: Not all bathroom membranes are suitable for floors and walls. Read the TDS.

☀️ External Areas (Balconies, Roof Decks, Planters)

External zones are exposed to:

• UV, temperature swings, and foot traffic.
• Wind-driven rain, ponding water, and full immersion conditions.

This means the membrane must be:

• UV stable and trafficable (or protected by finishes).
• Compatible with exterior adhesives and coatings.
• Installed over appropriate substrates (no particleboard!).
• Part of a system that manages drainage, movement, and outfalls.

💡 Tip: External applications are where under-designed membranes often fail fast — especially when the wrong falls or finishes are used.

⛏️ Below Ground Areas (Basements, Retaining Walls, Lift Pits)

Here, you're dealing with:

• Hydrostatic pressure (from soil and water pushing against the wall/floor),
• Rising damp, and
• Negative pressure (moisture moving from the outside in).

The system needs to:

• Include negative pressure membranes or Type A/B systems.
• Be backed up by drainage systems (like ag pipes, risers, or scuppers).
• Be resistant to soil movement, backfill damage, and immersion.

💡 Tip: These systems often fail because they're treated like a bathroom — they’re not. You need specialist membranes here.

Why Homeowners Should Care

If you've made it this far, you might be thinking "this sounds like the builder's job, not mine." But it's your bathroom, your balcony, and your repair bill if something goes wrong. Understanding the C13A Waterproofing Design Checklist is one of the most practical ways to protect your investment.

Waterproofing Failures Are Incredibly Expensive

Fixing a waterproofing defect costs far more than doing it right the first time. The QBCC reports that each bathroom claim finalised under the Queensland Home Warranty Scheme in 2024-25 averaged almost $25,000 in rectification costs.

Your home insurance generally won't cover it, and your builder may be long gone by the time it fails.

It’s a Hidden Defect — Until It’s Too Late

You can’t “see” a waterproofing failure until:

• The bathroom tiles start lifting,
• The paint starts bubbling,
• The skirting boards start warping, or
• Water starts dripping into the floor cavity.

By then it's not a patch job. It's demolition and reconstruction.

📋 It’s Not Your Job to Waterproof — But It Is Your Job to Ask

As the homeowner, you’re not expected to apply membranes or read technical data sheets — but you can ask smart questions:

• Has a waterproofing design checklist been completed?
• Are all products compatible and from the same manufacturer?
• What type of membrane is being used in each zone?
• Has the curing time and site condition been accounted for?

If your builder or waterproofer can't answer those clearly, that's your cue to dig deeper. The C13A checklist gives you the framework to do it.

It Helps You Hold the Builder Accountable

Documentation turns a promise into accountability. A completed checklist protects everyone, including a good builder.

With a completed checklist:

• You’ve got a record of what was used, why, and where.
• You can prove that the right questions were (or weren’t) asked.
• If something fails later, you’ve got evidence — not just a guess.

Plan It Properly, Waterproof It Once

Waterproofing isn't glamorous. It doesn't sparkle like stone benchtops or sell display homes like "Hamptons style" facades and multi-coloured LED strips synced to your Sonos. But it is one of the most common sources of costly defects in new homes.

The C13A Waterproofing Design Checklist gives builders, waterproofers and homeowners a shared tool to make decisions before work begins, avoid incompatible products, and document what was done and why. Use it. Share it. Ask for it.

How was that?

Waterproofing isn’t that hard. If you actually read and follow the instructions, you’re already ahead of 98% of people who don’t.

We're not done with waterproofing yet. The C13B Waterproofing Installation Checklist covers internal and external waterproofing installation.

Frequently Asked Questions (FAQ)

1. What’s the difference between waterproof and water-resistant?

Waterproof means no water gets through. Water-resistant means the material can handle some moisture, but not full immersion or pooling water. Waterproofing systems use both, depending on where they're installed.

Glossary

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2. Do all wet areas in a house need waterproofing?

Yes. Bathrooms, ensuites, laundries, and sometimes powder rooms must be waterproofed under AS3740:2021. If it’s a wet area, it needs protection.

3. What is a compatibility chain, and why does it matter?

It's the set of products (primer, membrane, sealant, tile adhesive and so on) that must work together as a system. If you mix brands or use products that aren't confirmed compatible, the membrane can fail, and the manufacturer's warranty won't cover it.

4. How can I tell if the waterproofing was done properly?

Ask to see the completed C13A checklist, the product data sheets, and photos taken during application. You can also engage an independent inspector for a flood test or to check Wet Film Thickness (WFT) during install.

5. Can one type of waterproofing membrane be used everywhere?

No. Internal, external, and below-ground areas each require different membranes based on exposure, pressure, and wear. A membrane that works in a bathroom may fail on a balcony or retaining wall.

6. What happens if waterproofing fails after handover?

Act quickly. Your contract gives you a defects liability period (12 months from practical completion under the standard QBCC new home contract) to have the builder fix it. In Queensland, the QBCC also treats defective work that lets water penetrate the building as a structural defect, which is covered by the Home Warranty Scheme for 6 years and 6 months. Records matter: photos, data sheets and a completed checklist make any claim much easier.

7. Is waterproofing covered in the standard building contract?

Usually, but the details (product choice, system used, documentation) are often vague or assumed. Builders and trades are meant to work to AS 3740 (internal wet areas) and AS 4654.2 (external above-ground areas), including the right paperwork. In Queensland, the paperwork you're likely to see is an aspect certificate (Form 43) from the licensed waterproofer, or an inspection certificate from the certifier or their inspector.

8. Who should complete the C13A checklist?

Ideally, the builder in consultation with the waterproofing contractor. It should be completed before work starts and signed off by the person supervising the job — and yes, you can ask to see it.

9. What’s the most common cause of waterproofing failure?

Poor substrate preparation, wrong curing conditions, incorrect wet and dry film thickness, no compatibility chain documentation, not checking relative humidity, surface moisture and surface temperature, and incompatible products. In other words, cutting corners. The checklist is designed to stop that.

10. How do I get a copy of the C13A checklist?

The C13A checklist is available as a print-ready PDF in our checklist series. Get the C13A Waterproofing Design Checklist. Use it as part of your build documentation to protect your home and your budget.

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Further Reading

A Introductory Guide to Waterproofing Wet Areas in Your HomeWaterproofing wet areas like bathrooms and laundry is crucial. This overview introduces to waterproofing concepts, from preparation to material selection and application. Learn basic waterproofing terms and methods.Understanding Waterproofing System Classes: A GuideLearn about waterproofing systems in residential construction. Learn about the classifications under Australian Standard AS 4654.1, their uses, and why choosing the right class is vital for the longevity and safety of your home.