Can I Waterproof a Laundry Trough Area Without a Tradesperson?

In most situations, a NZ homeowner can waterproof the area around a laundry trough without hiring a tradesperson — but only if no building consent is required and the work meets the NZ Building Code. Getting the waterproofing right is critical: a failed membrane behind a laundry trough can cause hidden moisture damage, mould, and costly repairs down the track.

What the NZ Building Code Requires

The NZ Building Code clause E3 (Internal Moisture) sets out requirements for controlling moisture inside buildings, including wet areas like laundries. The trough surround and any wall or floor surfaces that regularly get wet must be waterproofed to prevent moisture penetrating into the building structure.

For most laundry trough splash zones, this work falls under Schedule 1 of the Building Act, meaning it is exempt from building consent — but this is not automatic. The exemption applies when the work is like-for-like maintenance or minor repair. If you are retiling, reconfiguring the laundry layout, or doing significant alterations, you should check with your local council before starting, as consent may be required.

You can find guidance on what requires consent at MBIE Building Performance.

What Area Needs to Be Waterproofed?

As a general guide, the waterproofed zone around a laundry trough should cover:

• The wall surface directly behind and beside the trough — typically at least 150–200 mm beyond the trough edges and up to the underside of any overhead cabinetry or at least 1800 mm above the floor if it is a wet-splash area
• The floor area beneath and immediately around the trough if it is tiled or has a floor waste
• Any penetrations (pipe holes, fixings) which must be sealed before the membrane is applied

Always check the specific product's technical data sheet for minimum coverage requirements, as these vary.

Choosing the Right Waterproofing Product

For a laundry trough area, the most practical DIY-friendly options are liquid-applied membranes. These are brushed or rolled on and cure to form a flexible, waterproof layer. Common types available in NZ include:

Well-known NZ-available brands include products from Ardex, Mapei, and Sika. Always choose a product that is compliant with NZS 4858 (the NZ standard for wet area membranes) and follow the manufacturer's instructions precisely — including the number of coats, drying times, and reinforcing tape at corners and joints.

Step-by-Step: DIY Waterproofing Around a Laundry Trough

1. Prepare the Surface

• Remove the trough if possible, or work carefully around it
• Clean the wall and floor surfaces thoroughly — remove soap scum, grease, and any loose material
• Fill cracks or holes with a suitable filler and allow to cure fully
• Sand smooth if needed

2. Seal Penetrations

• Apply silicone sealant or the membrane manufacturer's recommended sealant around all pipe penetrations and fixings before applying the membrane

3. Apply Reinforcing Tape

• Press fibreglass reinforcing tape (supplied with most membrane kits) into the first coat of membrane at all internal corners, floor-to-wall junctions, and around penetrations
• This prevents cracking at stress points

4. Apply the Membrane

• Apply the first coat by brush or roller, working it into corners
• Allow to dry fully (check the data sheet — this can be 2–4 hours or overnight)
• Apply a second coat at 90° to the first
• Some products require a third coat in high-splash zones

5. Allow Full Cure Before Tiling or Reinstating

• Do not tile or refit the trough until the membrane has fully cured — typically 24–48 hours minimum, but check the product instructions

Healthy Homes and Rental Properties

If the laundry is in a rental property, the Healthy Homes Standards require landlords to maintain the property in a reasonable state of repair, which includes preventing moisture ingress. Proper waterproofing is part of meeting this obligation.

When to Call a Professional

While DIY waterproofing is achievable for a straightforward laundry trough splash zone, you should hire a qualified waterproofer or tiler if:

• The existing waterproofing or substrate is badly damaged or mouldy
• You are retiling the entire laundry or making layout changes (check if consent is needed)
• The area involves a floor waste or floor-level shower (more complex membrane detailing required)
• You are unsure whether the substrate (e.g. old fibre cement, plasterboard) is suitable
• The work is in a multi-unit building or apartment where body corporate rules may apply

For plumbing connections to the trough (water supply and waste pipes), this is restricted work under the Plumbers, Gasfitters and Drainlayers Act and must be carried out by a licensed tradesperson registered with the Plumbers Gasfitters & Drainlayers Board. A homeowner may not legally connect or alter water supply or drainage pipework.

You can find experienced local waterproofers and tilers on tradedirectory.co.nz.

Sources & Further Reading

• MBIE Building Performance — Building Code and consents
• BRANZ — Wet area construction guidance
• Ardex NZ — Waterproofing membranes
• Sika NZ — Waterproofing products
• Plumbers Gasfitters & Drainlayers Board — Licensed tradespeople
• Tenancy Services — Healthy Homes Standards