If you've ever watched a professional painter prep a room, you've probably seen them wipe down walls before they even crack open a tin of paint. That cleaning step almost always involves sugar soap — and skipping it is one of the most common mistakes DIY painters make. Here's everything you need to know about sugar soap and how to use it properly.
What Is Sugar Soap?
Sugar soap is an alkaline cleaning solution used to degrease and clean surfaces before painting. Despite the name, it contains no actual sugar. The name comes from its appearance in powdered form — it looks a bit like raw sugar crystals. It's available as a powder you mix with water or as a ready-to-use liquid spray, and you'll find it at Bunnings, Mitre 10, and most paint stores.
Sugar soap works by breaking down grease, cooking oils, nicotine residue, scuff marks, and general grime that builds up on walls, ceilings, woodwork, and other paintable surfaces. Because paint needs a clean, slightly abraded surface to bond to, any contamination left behind can cause peeling, poor adhesion, or an uneven finish.
Why Surface Preparation Matters
Professional painters will tell you that preparation is at least half the job. BRANZ, New Zealand's building research authority, consistently highlights surface preparation as critical to paint durability. A coat of paint applied over a greasy or dirty surface may look fine initially but is far more likely to peel, bubble, or chip within a year or two — especially in high-humidity areas like kitchens and bathrooms.
Sugar soap is the go-to first step because it's affordable, effective, and safe for most interior and exterior surfaces when used correctly.
When Should You Use Sugar Soap?
Use sugar soap in the following situations:
- Before any interior repaint — walls and ceilings accumulate dust, grease, and fingerprints over time
- Kitchen and dining areas — cooking grease is notorious for preventing paint adhesion
- Bathrooms and laundries — soap scum and moisture residue need to be removed
- Woodwork, skirting boards, and door frames — these collect handling marks and polish residue
- Before painting over gloss or semi-gloss paint — sugar soap helps dull the sheen and improves adhesion (though you'll still want to lightly sand as well)
- Nicotine-stained walls — heavy smoker residue must be cleaned thoroughly before priming
- Exterior prep — before repainting weatherboards, fascias, or trim, especially if there's mould or mildew present (combine with a mould treatment if needed)
How to Use Sugar Soap: Step-by-Step
What you'll need
- Sugar soap (powder or liquid)
- Two buckets (one for solution, one for rinsing)
- Warm water
- Large sponge or cloth
- Rubber gloves
- Drop sheets to protect floors
The process
- Mix your solution — if using powder, follow the packet directions. For general cleaning, a standard dilution in warm water is typical. For heavy grease or nicotine, use a stronger mix.
- Protect the area — lay drop sheets and remove or cover furniture.
- Work top to bottom — start at the ceiling and work down to avoid dirty drips running over clean areas.
- Wash in sections — apply the sugar soap solution with a sponge using firm, circular motions. Don't saturate the surface, especially on plasterboard (GIB).
- Rinse thoroughly — this step is critical. Use clean warm water and a fresh sponge to remove all sugar soap residue. Leftover residue can affect paint adhesion just as much as the original grime.
- Allow to dry completely — don't rush this. Painting over a damp surface is a recipe for problems. Allow adequate drying time, which will vary depending on ventilation and humidity.
Sugar Soap vs Other Cleaners
| Cleaner | Best for | Notes | |---|---|---|| | Sugar soap | General pre-paint prep, grease, grime | Rinse thoroughly after use | | TSP (trisodium phosphate) | Heavy-duty degreasing | Less common in NZ; handle with care | | Mild detergent | Light dust and surface dirt | May leave residue; not ideal before painting | | Mould killer / bleach solution | Mould and mildew | Use before sugar soap if mould is present |
Tips for Best Results
- Always wear rubber gloves — sugar soap is alkaline and can irritate skin with prolonged contact.
- Ventilate the room — open windows and doors while you work.
- Don't skip the rinse — this is the step most DIYers rush, and it causes problems later.
- Check for mould first — if you spot mould, treat it with an appropriate mould and mildew solution before sugar soaping. Resene and Dulux both offer pre-paint mould treatments.
- Follow up with a quality primer where needed, particularly on bare or patched surfaces.
When to Call a Professional
Sugar soaping is well within the scope of a capable DIYer. However, if you're dealing with extensive mould (which may indicate a moisture or ventilation issue), lead paint on older homes (pre-1980s), or you're preparing surfaces as part of a larger renovation, it's worth getting a professional painter involved. A qualified painter will assess the full condition of your surfaces and recommend the right prep, primer, and paint system for a lasting result. You can find experienced local painters on tradedirectory.co.nz.
Lead paint warning: If your home was built before 1980, there's a chance older paint layers contain lead. Sanding or disturbing lead paint is a health hazard — check with WorkSafe NZ for guidance before proceeding.