Adding colour pigment to concrete is well within reach of a capable DIYer, provided you measure carefully and follow a consistent process. The key to success is accurate dosing, thorough mixing, and keeping every batch identical — because even small variations in water content or pigment quantity will show up as colour differences once the concrete cures.
Understanding Concrete Pigments
Concrete pigments are finely ground colouring agents — most commonly iron oxide powders — that are blended into the concrete mix before it sets. They are UV-stable, alkali-resistant, and won't fade the way surface paints can. You'll find pigments available in powder, liquid, and granule forms at most NZ trade and hardware stores.
Common colour families include:
- Reds, browns, and yellows — iron oxide based, very stable
- Blacks — carbon black or black iron oxide
- Greens and blues — chromium oxide or synthetic pigments (less common, can be pricier)
White cement can be used as the base instead of standard grey cement if you want lighter, brighter colours. Grey cement will dull pastel shades considerably.
What You'll Need
- Concrete pigment (powder or liquid)
- Portland cement, aggregate, and sand (or a bagged concrete mix)
- Accurate scales or measuring cups
- Mixer (electric drum mixer strongly recommended for consistency)
- Water
- Protective gloves, safety glasses, and a dust mask (P2 rated)
- Consistent measuring containers — one set per batch
You can source pigments and bagged concrete mixes from Bunnings, Mitre 10, or PlaceMakers.
Pigment Dosage: Getting the Ratio Right
The standard rule of thumb is to add pigment at 2–10% of the cement weight — not the total mix weight. Going above 10% rarely deepens the colour further and can weaken the mix.
| Desired Intensity | Pigment (% of cement weight) |
|---|---|
| Subtle / pastel | 2–4% |
| Medium tone | 4–7% |
| Deep / rich colour | 7–10% |
Always weigh your pigment on scales rather than estimating by eye. For a 20 kg bag of cement at 5% loading, you'd add 1 kg of pigment. Write down your exact quantities and repeat them precisely for every batch.
Step-by-Step Mixing Process
1. Prepare a test batch first
Before committing to a large pour, mix a small test batch, cast it into a mould, and let it cure for at least 7 days. Wet concrete looks much darker than cured concrete, so always judge colour from a cured sample.
2. Dry-mix the pigment with cement
Add the measured pigment to the dry cement and blend them together before adding aggregate or water. This helps distribute the colour evenly throughout the mix.
3. Add aggregate, then water
Combine your pigment-cement blend with sand and aggregate, then add water gradually. Use the same water-to-cement ratio every batch — excess water lightens and weakens the final colour. A lower water-to-cement ratio generally produces a richer, more consistent result.
4. Mix thoroughly
Mix for at least 3–5 minutes in a drum mixer after all ingredients are combined. Inconsistent mixing leads to streaking and blotchy colour.
5. Pour and finish as normal
Place, screed, and finish your coloured concrete as you would standard concrete. Avoid overworking the surface, which can bring excess water to the top and cause colour variation.
Curing and Sealing
Proper curing is critical for both strength and colour consistency. Keep the surface moist and covered with plastic sheeting or a curing compound for at least 7 days. In hot NZ summers, concrete can dry out too quickly — shade the pour if possible.
Once fully cured (28 days for full strength), applying a penetrating concrete sealer will protect the colour and make the surface easier to clean. Sika and Ardex both offer concrete sealers suitable for NZ conditions — check manufacturer datasheets for the right product for your application.
Tips for Consistent Results
- Batch size matters — mix only what you can pour in one session to avoid cold joints and colour variation between pours
- Label and store leftover pigment in a sealed container away from moisture
- Use the same brand and type of cement throughout the job — switching brands mid-project can shift the base colour
- Keep notes on every batch: pigment weight, cement weight, water volume, and mix time
Safety Notes
Concrete is highly alkaline and can cause serious skin and eye burns. Always wear waterproof gloves, safety glasses, and a P2 dust mask when handling dry cement and pigment powders. Refer to WorkSafe NZ guidance on working safely with cement and silica dust.
When to Call a Professional
DIY pigmented concrete works well for smaller projects like garden paths, stepping stones, or decorative panels. For larger structural slabs, driveways, or anything that requires a building consent, it's worth engaging a qualified concreter. Structural concrete work may need to comply with the NZ Building Code and relevant standards — always check with your local council whether consent is required before you start.
If you want a more complex finish — such as exposed aggregate, stamped patterns, or acid staining over pigmented concrete — a professional will have the tools and experience to get a reliable result. You can find qualified local concreters on tradedirectory.co.nz.
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