Yes, you can use premixed compound for finishing — and for most DIY finishing work it's actually the easier choice. However, setting compound and premixed compound behave quite differently, and understanding those differences will help you get a smooth, professional result on your plasterboard walls and ceilings.
What's the Difference Between the Two?
Premixed compound (sometimes called "ready-mix" or "joint compound") comes in a bucket, ready to use straight away. It dries by evaporation, which means it shrinks slightly as moisture leaves the material. It's easy to sand, forgiving for beginners, and widely available at stores like Bunnings and Mitre 10.
Setting compound (often sold as a powder you mix with water, sometimes called "hot mud") cures by a chemical reaction rather than evaporation. It sets hard within a defined time window — typically 20, 45, or 90 minutes depending on the product — and shrinks far less than premixed. Once set, it's much harder to sand.
When Premixed Compound Works Best
Premixed compound is ideal for:
- Finish coats — the final one or two thin coats over a primed surface
- Skim coats — feathering out edges and blending joints
- Texture work — where a slightly softer, workable material is an advantage
- DIY projects — where you want more working time and easy sanding
Because it shrinks slightly as it dries, premixed compound is generally not recommended as a standalone product for filling deep gaps or embedding tape in a single thick application. Shrinkage in thick coats can cause cracking.
When Setting Compound Has the Edge
Setting compound is preferred by professional plasterers for:
- Embedding fibreglass mesh tape — the chemical set bonds firmly and resists cracking
- First (base) coats over joints and fastener heads — minimal shrinkage means fewer coats needed
- Repairs in high-humidity areas — it's more moisture-resistant once cured
- Fast turnaround — a 20- or 45-minute setting compound lets you apply the next coat the same day
For a standard three-coat plasterboard finishing system (as outlined in GIB's technical literature), many tradespeople use setting compound for the first coat and switch to premixed for the second and finish coats. This combines the strength of setting compound with the easy sanding of premixed.
A Practical Guide to Coats
| Coat | Recommended Product | Notes |
|---|---|---|
| First (embed) coat | Setting compound or premixed | Setting compound preferred for tape embedding |
| Second (fill) coat | Premixed or setting compound | Apply once first coat is fully dry/set |
| Finish coat | Premixed | Thin, feathered out; easy to sand smooth |
Tips for Using Premixed Compound
- Don't apply it too thick. Keep each coat to around 1–2 mm. Thick coats shrink and crack.
- Allow full drying time. In New Zealand's cooler or more humid climates — particularly in the South Island or during winter — drying can take 24 hours or more per coat. Don't rush it.
- Keep the lid on. Premixed compound dries out quickly once exposed to air. Store it in a cool place and press plastic wrap against the surface before sealing the lid.
- Stir before use. Separation can occur in storage.
- Sand between coats with fine-grit paper (around 120 grit) once fully dry, then wipe away dust before the next coat.
- Prime before painting. Plasterboard compound is porous and must be sealed with a suitable primer — check with Resene or Dulux for their recommended plasterboard primers before applying your topcoat.
NZ Building Code Considerations
If your plastering work is part of a larger building project, it's worth checking whether a building consent is required. Internal lining work is often exempt under Schedule 1 of the Building Act, but always confirm with your local council before starting. MBIE Building Performance has useful guidance on consent requirements.
For plasterboard installation and finishing, GIB's technical documentation is the go-to NZ reference for correct installation methods, including joint treatment systems that comply with the NZ Building Code.
Healthy Homes and Moisture
In rental properties, wall and ceiling linings must be in good condition under the Healthy Homes standards. If you're repairing or finishing walls in a bathroom or laundry, make sure you're using moisture-resistant plasterboard and appropriate compound — standard premixed compound is not suitable for wet areas.
When to Call a Professional
Plastering looks straightforward but achieving a truly flat, blemish-free finish takes practice. If you're working on a large area, a new build, or a high-visibility space like a living room or hallway, it's worth getting a qualified plasterer involved. Poor finishing shows up badly under raking light once paint is applied — and fixing it later costs more than getting it right the first time.
You can find experienced, local plasterers on tradedirectory.co.nz who can advise on the right products and techniques for your specific project.
Note: Plastering is not restricted work under NZ law, so homeowners can legally do their own plasterboard finishing. However, if your project involves any electrical work (such as relocating light fittings or power points), that must be carried out by a registered electrician — see EWRB for details.
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