Washing your walls before painting isn't just a nice-to-have step — it's one of the most important things you can do to ensure your paint job lasts. Dust, grease, mould, and grime all prevent paint from bonding properly to the surface, leading to peeling, bubbling, and patchy coverage. Whether you're freshening up a lounge or repainting a kitchen, a clean wall is the foundation of a professional-looking result.
Why Wall Washing Matters
Paint is designed to adhere to a clean, stable surface. Even walls that look clean to the naked eye can carry a thin film of dust, cooking grease, or airborne contaminants — especially in kitchens, bathrooms, and hallways. If you paint over these, you're essentially gluing your new coat to the dirt rather than the wall itself. The result is poor adhesion, which shows up as peeling or flaking within months.
BRANZ, New Zealand's building research authority, consistently highlights surface preparation as the single biggest factor affecting paint durability. Skipping this step is a false economy.
What You'll Need
- Sugar soap (the go-to cleaner for walls — available at Bunnings or Mitre 10)
- Two buckets (one for cleaning solution, one for rinsing)
- Large sponges or a soft cloth
- Rubber gloves
- Drop cloths to protect floors
- A mould treatment product if mould is present
- Fine-grit sandpaper (for any rough patches after drying)
Step-by-Step: How to Wash Your Walls
1. Clear and protect the room
Move furniture away from walls and lay drop cloths on the floor. Remove switch plates and power point covers where possible.
2. Dust first
Use a dry microfibre cloth or a vacuum with a brush attachment to remove loose dust and cobwebs. Start from the top and work down. Skipping this step means you'll just be pushing wet dust around.
3. Mix your sugar soap solution
Follow the dilution instructions on the packet — sugar soap is typically mixed with warm water. It's alkaline, so it cuts through grease and grime effectively without leaving a residue that would interfere with paint adhesion.
4. Wash from the bottom up
This sounds counterintuitive, but washing from the bottom up prevents dirty water from running down over dry sections and leaving streaks that are hard to remove. Work in manageable sections.
5. Rinse thoroughly
Use your second bucket of clean water to rinse each section before it dries. Sugar soap residue left on the wall can affect paint adhesion just as much as the original grime.
6. Allow to dry completely
This is critical. Painting over a damp wall traps moisture, which can cause blistering and mould growth behind the paint film. Allow at least a few hours of drying time — longer in cooler or more humid conditions, which are common in many parts of New Zealand.
Dealing With Mould and Mildew
Mould is a significant issue in many NZ homes, particularly in older houses with limited ventilation or in regions with high humidity. If you spot mould on your walls, sugar soap alone won't cut it.
Treat mouldy areas with a dedicated mould killer or a diluted bleach solution (follow product instructions carefully and ensure good ventilation). Allow the treatment to work, then rinse and dry before painting. When you repaint, use a mould-resistant paint — both Resene and Dulux offer interior paints with mould inhibitors suited to NZ conditions.
If mould keeps returning despite treatment, it may indicate a moisture or ventilation problem that needs addressing first. Under the Healthy Homes Standards, rental properties must meet specific ventilation requirements — worth keeping in mind if you're a landlord.
Surface-by-Surface Guide
| Surface | Recommended Cleaner | Extra Notes |
|---|---|---|
| General interior walls | Sugar soap solution | Rinse well, dry fully |
| Kitchen walls | Sugar soap (stronger mix) | Degrease thoroughly near cooktop |
| Bathroom walls | Mould treatment + sugar soap | Check for mould behind fittings |
| Gloss or semi-gloss paint | Sugar soap + light sand | Sanding improves adhesion |
| New plasterboard (GIB) | Light dust only | May not need washing |
| Exterior weatherboards | Hose down + sugar soap | Check for mould and chalking |
What About New Walls?
Brand new GIB plasterboard that has just been stopped and sanded generally doesn't need washing — just make sure it's free of dust from sanding. However, if the surface has been handled a lot during construction, a light wipe-down is still worthwhile.
New timber or previously unpainted surfaces may need a primer rather than just a wash — check the paint manufacturer's recommendations.
Common Mistakes to Avoid
- Painting over grease in kitchens — this is the number one cause of paint failure in that room
- Not rinsing after sugar soap — residue causes adhesion problems
- Painting on a damp wall — always allow adequate drying time
- Ignoring mould — painting over it without treatment means it will return
- Using harsh abrasive cleaners — these can damage the existing paint surface or leave scratches
When to Call a Professional
Most wall washing is well within DIY capability. However, if you're dealing with extensive mould that keeps returning, it may point to a structural moisture issue — a builder or plasterer should assess this before you repaint. If you're painting near electrical fittings, switchboards, or light fittings, take care around these areas. Any actual electrical work — such as moving or replacing fittings — must be carried out by a registered electrician under the Electrical Workers Registration Board rules; this is restricted work under NZ law.
For large repaints, multi-storey homes, or if you simply want a guaranteed professional result, it's worth getting a qualified painter involved. You can find experienced local painters on tradedirectory.co.nz.