For most shower floors, you'll need a minimum of two coats of liquid waterproofing membrane, though many waterproofing professionals and product manufacturers recommend three coats — especially in high-use or tiled wet areas. The exact number depends on the product you're using, the substrate, and the requirements of the NZ Building Code, particularly Clause E3 (Internal Moisture).
Why the Number of Coats Matters
A liquid membrane works by building up a continuous, flexible film that prevents water from penetrating the substrate beneath your tiles. If the film is too thin — whether from skipping a coat or applying coats too thickly in one go — you risk pinholes, thin spots, and eventual leaks. Water ingress in a shower can cause serious structural damage, mould, and rot, so getting this right from the start is critical.
The goal is to achieve the minimum dry film thickness (DFT) specified by the manufacturer. This is typically between 0.8 mm and 1.5 mm for shower floors, but always check your specific product's technical data sheet.
Standard Coat Requirements for Shower Floors
Here's a general guide to how coats are typically applied:
| Stage | What Happens |
|---|---|
| Coat 1 (Primer or first coat) | Seals the substrate and provides adhesion for subsequent coats |
| Coat 2 (Main coat) | Builds up the bulk of the membrane thickness |
| Coat 3 (Top/finish coat) | Ensures full coverage, fills any pinholes, meets minimum DFT |
| Reinforcing fabric | Embedded in the first or second coat at junctions, corners, and penetrations |
Some products are formulated to achieve the required DFT in two coats, while others need three. Never assume — always read the product data sheet.
NZ Building Code and E3 Requirements
Under MBIE Building Performance guidelines, shower floors are classified as wet areas and must be waterproofed to comply with Clause E3 (Internal Moisture). The acceptable solution most commonly referenced is E3/AS1, which requires that wet area waterproofing be installed in accordance with the membrane manufacturer's instructions and achieve a continuous, defect-free film.
BRANZ research and guidance also reinforces that corners, junctions, and penetrations (like the drain) are the most common failure points — these areas should always receive reinforcing membrane tape or fabric embedded into the wet membrane before subsequent coats are applied.
Drying Time Between Coats
This is where many DIYers go wrong. Applying the next coat before the previous one has properly cured can trap moisture and compromise adhesion. As a general guide:
- Allow 2–4 hours between coats in normal conditions (around 20°C, good ventilation)
- In cooler or humid conditions (common in many NZ homes in winter), allow longer — check the product data sheet
- Do not rush the process by using heat guns or fans directly on the membrane
- The final coat should cure for the manufacturer's recommended period (often 24–48 hours) before tiling begins
Choosing the Right Product
Several reputable waterproofing products are available in New Zealand. Look for products that are specifically rated for wet area / shower floor use and comply with AS/NZS 4858 (Wet area membranes). Common options available at Bunnings or Mitre 10 include products from Ardex, Mapei, and Sika — all of which publish detailed technical data sheets specifying the exact number of coats and DFT requirements for their products.
PlaceMakers also stocks a range of trade-grade waterproofing systems if you want access to professional-quality materials.
Key Areas That Always Need Extra Attention
- Floor-to-wall junctions — apply reinforcing tape and an extra coat
- Around the drain — use a drain collar or membrane flange and seal carefully
- Internal corners — cove or fillet these before waterproofing
- Any penetrations — pipes, fixings, and outlets all need careful detailing
Skimping on these areas is the number one cause of shower leaks in NZ homes.
Is Waterproofing a Shower DIY or Restricted Work?
Waterproofing a shower floor is not restricted building work in New Zealand, so a competent homeowner can legally do it themselves. However, if the work is part of a larger renovation involving plumbing, drainage, or electrical work, those elements must be carried out by a licensed tradesperson — see the Plumbers Gasfitters & Drainlayers Board and the Electrical Workers Registration Board for what's restricted.
Note that some shower installations may require a building consent — always check with your local council before starting significant bathroom work.
When to Call a Professional
If you're unsure about the substrate condition, have an existing leak to diagnose, or are tiling over a timber floor (which requires careful assessment), it's well worth calling a qualified waterproofer. A professional will ensure the membrane is applied correctly, the DFT is achieved, and the installation meets the NZ Building Code — protecting your home and your investment. You can find experienced local waterproofing tradespeople on tradedirectory.co.nz.
Safety note: Many liquid membranes contain solvents or isocyanates. Always work in a well-ventilated space, wear appropriate PPE (gloves, eye protection, and a respirator if specified), and follow the safety data sheet. Check WorkSafe NZ for guidance on safe handling of construction chemicals.
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