What is waterproofing? It is the system of membranes, sealants and falls that stops water getting into a building where it can rot timber, stain walls and grow mould. In Sydney it matters on balconies, showers, laundries, roofs and below-ground walls, and the cost depends on the area, the access and the membrane (indicative — get itemised quotes).
This guide explains what waterproofing is, the main types, balcony and laundry rules, the NSW certificate, a quick look at Crommelin products, and what to check before you hire a licensed waterproofer.
Key points
- Waterproofing is a layered system of surface preparation, membrane, falls and flashings, and it only works when each layer is done to the manufacturer’s directions.
- Balconies, showers and laundries are high-risk areas, so use a licensed waterproofer and keep the certificate of compliance for your records.
- A paint-on product or hardware-store sealant is not a substitute for a full membrane in a wet area or over habitable space.
- Cheap shortcuts show up later as leaks, mould and ruined tiles, so compare itemised quotes and ask what standards and products they follow.
What is waterproofing?
What is waterproofing in a house? It is a continuous barrier that keeps water out of the structure behind tiles, slabs and cladding. Without it, moisture finds the weak point and rots or corrodes what it touches.
A good job has more than a membrane. It also needs a sound, clean surface, correct falls to a drain, and flashings that lap over the edges.
- Substrate: a sound, clean, dry base such as concrete, fibre cement or sheet flooring, free from dust, oil and loose material.
- Primer: a bonding coat that helps the membrane grip, used only if the product maker requires it.
- Membrane: the actual waterproof layer, applied liquid, sheet or torch-on, depending on the product.
- Bond breakers and reinforcement: bandages and corner pieces at joins, which stop cracks from opening through the membrane.
- Falls and drainage: a slope toward the drain, so water leaves rather than ponding on the surface.
- Protection and finish: tiles, screed or a topcoat that protects the membrane from wear and sunlight.
Types of waterproofing
What is waterproofing made of? There are several types, and each suits a different part of the building. Choose by location, movement and exposure, not just price.
| Type | Best for | Lifespan / strength | Price band |
|---|---|---|---|
| Liquid-applied membrane | Showers, laundries and balconies | Flexible, joint-free coat; strength depends on correct coats and cure | $$ (indicative — get itemised quotes) |
| Sheet membrane | Large flat areas and planters | Consistent thickness, needs careful joins | $$ to $$$ (indicative — get itemised quotes) |
| Torch-on bitumen membrane | Flat roofs and basements | Tough, but needs a licensed applicator for hot work | $$ to $$$ (indicative — get itemised quotes) |
| Cementitious coating | Below-ground walls and tanks | Rigid, can crack with movement | $$ (indicative — get itemised quotes) |
| Roof sealant or coating | Gutters, flashings and minor roof repairs | Short- to mid-term repair, not a full replacement | $ to $$ (indicative — get itemised quotes) |
| Waterproof paint or sealer | Masonry that is damp but not under pressure | Reduces absorption, never replaces a membrane | $ (indicative — get itemised quotes) |
Our insulation types guide explains how moisture control and insulation work together in the roof and walls.
House waterproofing cost
House waterproofing cost is driven by area, access, substrate repairs and the membrane. Treat every range here as a starting point.
| Item | What drives the price | Typical range |
|---|---|---|
| Shower or bathroom floor and walls | Size, number of penetrations and tile removal | Mid range per room (indicative — get itemised quotes) |
| Laundry floor | Floor area, drain position and door threshold | Mid range per room (indicative — get itemised quotes) |
| Balcony or deck over a room | Area, access, substrate and tile removal | Upper range per square metre (indicative — get itemised quotes) |
| Flat roof or planter box | Area, falls and membrane type | Mid to upper range (indicative — get itemised quotes) |
| Below-ground wall | Depth, drainage and excavation | Varies widely (indicative — get itemised quotes) |
| Substrate repair and demolition | Rot, cracks and old tile removal | Adds to the quote (indicative — get itemised quotes) |
- Area and access: a small bathroom costs less per square metre than a large balcony that needs scaffold or crane access.
- Existing condition: rotten substrate, cracked slabs and failed old membranes all add repair work before waterproofing starts.
- Membrane choice: premium products and extra coats cost more, but cheap options can fail early.
- Tile removal: stripping old tiles and screed is slow, dusty work and drives labour costs.
- Cure and test time: extra days for curing and flood tests add to the schedule, and rushing them is a common cause of leaks.
- Compliance paperwork: a licensed waterproofer’s certificate is part of a proper job and should be in the quote.
Waterproofing pros and cons
Waterproofing is a protective investment, not a finish. Weigh these points against the cost of a failed wall or floor.
Pros of proper waterproofing
- Protects timber, steel and plaster from rot, rust and mould.
- Reduces the chance of leaks into rooms below a balcony or bathroom.
- Helps meet building rules and keeps your paperwork in order for sale.
- Extends the life of tiles, paint and floor coverings.
- Gives you a documented warranty from the installer and the maker.
- Costs far less than rebuilding after long-term water damage.
Cons and limits
- Adds upfront cost and time to a renovation.
- Needs correct preparation, or the membrane can peel or blister.
- Cannot fix a structural fault or a poorly drained design.
- Needs inspection and maintenance, especially at edges and drains.
- Repairs to a hidden leak usually involve removing tiles.
- Poor workmanship is hard to see until water appears.
How to choose waterproofing
Start by asking what is waterproofing protecting in this location, then match the product and the installer to it. Work through this checklist before you accept a quote.
- Define the area: shower, laundry, balcony, roof or below-ground wall, because each has different rules and products.
- Check licensing: ask for the contractor’s licence number and confirm it with NSW Fair Trading.
- Ask about standards: a good contractor can name the Australian Standard they follow for your area.
- Review the system: ask for the product data sheet, the number of coats and the cure time.
- Request the certificate: confirm you will receive a certificate of compliance after the work.
- Compare itemised quotes: check that tile removal, substrate repair and testing are listed.
Waterproofing essentials: preparation, application and testing
Preparation decides how long a waterproofing job lasts. A licensed waterproofer will follow the manufacturer’s data sheet at every step.
- Inspect the substrate for rot, cracks and loose material, and repair them before any product goes on.
- Clean and dry the surface so dust, oil and moisture do not stop the membrane bonding.
- Set the falls toward the drain, using a screed if needed, so water drains away.
- Apply primer and reinforcement at corners, hobs and drain outlets as the system requires.
- Apply the membrane in the number of coats the data sheet states, and allow the full cure time between them.
- Flood test and record the result, then tile or finish only after the test passes and the waterproofer signs off.
Balcony waterproofing: what is waterproofing under AS4654.2?
What is waterproofing on a balcony? It is a membrane under the tiles or deck that keeps water out of the rooms below. AS4654.2 is the Australian Standard that covers the design and installation of external above-ground membranes, and good installers follow it.
- Falls and drainage: confirm the balcony slopes to a drain or an outlet, because ponding water finds the weakest join.
- Upstands and flashings: membrane should turn up at walls and doors, and be covered by flashings so water cannot run behind it.
- Movement joints: large balconies need joints that match the movement of the slab and tiles.
- Tile and adhesive: choose products the membrane maker approves, because incompatible adhesive can damage the coating.
- Testing: a flood test before tiling shows leaks while repairs are still easy.
- Balcony decks and cladding: check boards and lining are suited to outdoor use; see our WPC composite cladding guide.
NSW waterproofing certificate and licensing
In NSW, waterproofing work is a regulated trade, so use a licensed contractor and ask for the documentation. Confirm the current requirements with NSW Fair Trading before work begins.
- Licensed contractor: ask for the licence number and confirm it with NSW Fair Trading before work starts.
- Certificate of compliance: a licensed waterproofer provides a certificate once the work is done, and you should keep it with your house records.
- Why it matters: certifiers, insurers and buyers may ask for it, and it shows the work was done to the standard.
- Work done without one: a missing certificate can complicate a sale or an insurance claim after a leak.
- Building approvals: check with your council or certifier whether your project needs approval.
- Warranty: keep the product data sheet and the installer’s warranty in writing.
Waterproofing a laundry: Australian standards
Australian standards waterproofing laundry rules sit within the National Construction Code and the Australian Standard for waterproofing of domestic wet areas. A licensed waterproofer will know which clauses apply to your layout.
- Floor membrane: the laundry floor generally needs a membrane that runs up the walls and across the door threshold.
- Wall treatment near taps and tubs: splash zones around the trough and washing machine need protection.
- Floor waste and falls: set the falls to the floor waste, so water drains rather than pools.
- Penetrations: seal pipes and drains with the system’s collars, and leave plumbing connections to a licensed plumber.
- Linings: use wet-area rated boards as the maker directs, and see our internal wall cladding ideas for lining options.
- Finishes: tile or sheet vinyl must be installed over a cured, tested membrane.
Crommelins waterproofing and other membrane brands
Crommelins waterproofing refers to the Crommelin range of Australian membranes and sealants sold through trade suppliers. Brand matters less than correct use, so compare data sheets rather than names.
| Check | What to ask | Why it matters |
|---|---|---|
| Intended use | Is the product rated for your area, such as a shower or a balcony? | A product for a planter may not suit a shower |
| System components | Which primer, bandage and topcoat does the maker require? | Mixing brands can void the warranty |
| Coats and cure time | How many coats, and how long before tiling? | Rushing the cure is a common cause of failure |
| Standards | Does the product list the Australian Standard it meets? | Shows the product is designed for the job |
| Compatibility | Is your tile adhesive approved by the maker? | Wrong adhesive can attack the membrane |
| Warranty | What are the written terms and who applies it? | Cover often depends on a licensed installer |
Roof plastic sheet and roof waterproofing
Roof plastic sheet usually means polycarbonate patio sheeting, which keeps rain out but is not a membrane. Follow the maker’s rules for pitch, laps and fixings so the roof sheds water.
- Minimum pitch: corrugated polycarbonate needs at least 5 degrees, about 88 mm rise per lineal metre, or water will not drain.
- Laps and fixings: follow the maker’s side and end lap rules, and use the supplied fixings to keep the warranty valid.
- Do not walk on sheets: use stepping boards, because sheets crack under body weight.
- Steel roofs: metal roof sheets are a different system; see our custom orb corrugated guide.
- Detail at walls: a flashing is needed where the sheet meets a wall, so water cannot get behind.
- More detail: read the polycarbonate roofing guide for spans, laps and fixings.
Painting and lining over waterproofed surfaces
Painting and lining come after waterproofing, and they must not damage the membrane. Paint is a finish, not a waterproofing layer.
- Use compatible paints: check with the membrane maker before painting an exposed coating.
- Choose the right whites: for ceilings and walls, our Lexicon Quarter vs Half vs Full guide explains the strengths.
- Avoid timber panelling in wet rooms: see the VJ panelling guide for dry-room use and finishing.
- Do not pierce the membrane: screws and fixings through the coating must be sealed by the waterproofer.
- Inspect yearly: look for cracked grout, lifted tiles and stains below balconies.
- Act on early signs: bubbling paint, musty smells and damp patches mean it is time for a licensed inspection.
Common waterproofing mistakes to avoid
- Using paint as a membrane: waterproof paint reduces absorption but does not seal a wet area.
- Skipping the flood test: a quick test shows leaks while repairs are cheap.
- Tiling too early: uncured membrane can bubble or fail under tile adhesive.
- Ignoring falls: water that pools finds its way into joins and corners.
- Using an unlicensed trade: work without a licence can leave you with no certificate and no recourse.
- Waterproofing over rot: a membrane cannot fix damaged timber or a cracked slab.
Waterproofing FAQs
What is waterproofing?
What is waterproofing in simple terms? It is a barrier system that stops water passing through a floor, wall or roof. It combines a prepared surface, a membrane, correct falls and flashings. When any layer is wrong, water finds a path, so careful preparation matters as much as the product.
Can I waterproof a balcony myself?
A balcony over habitable space is a high-risk area, so book a licensed waterproofer. The work must meet the Australian Standard, include correct falls and flashings, and finish with a certificate. A DIY job can leave you with leaks and no paperwork if you sell.
Do I need a waterproofing certificate in NSW?
For regulated waterproofing work, a licensed waterproofer provides a certificate of compliance once the job is complete. Keep it with your records. Requirements can change, so confirm the current rules with NSW Fair Trading, your council or a certifier before you start.
Is waterproof paint enough for a bathroom?
No. Waterproof paint reduces water absorption but does not replace a wet-area membrane under the tiles. Showers and bathroom floors need a licensed waterproofer to apply a full system. Use paint as a finish over sound, dry walls outside the wet zones only.
What Australian standard applies to laundry waterproofing?
Laundries are covered by the National Construction Code and the Australian Standard for waterproofing of domestic wet areas. A licensed waterproofer will know which provisions apply to your layout. Ask them to explain how the floor, walls and door threshold will be treated.
How long does waterproofing last?
Life depends on the system, the preparation and the movement of the structure. A well-installed membrane can last many years, but cracked grout, failed sealant and blocked drains shorten it. Inspect yearly, keep your warranty paperwork and book a licensed inspection at the first sign of damp.
Getting waterproofing done in Sydney
Waterproofing works when each layer is done right and tested before tiling. We coordinate licensed trades across Sydney for roof repairs, flashings and waterproofing, with itemised quotes and workmanship cover. Book a free inspection and quote.
