Where Can I buy Iron Oxide in NZ?

Oxide pigment is an iron oxide powder used as a dye or colourant in ceramics, paint, concrete, coatings, inks, leather, plastics, and rubber. You can add it to glazes, use it as pigment powder in varnishes, or mix it into paint. In cement, mortar, and plaster, iron oxide colours the mixture. For best results, use 4% iron oxide by cement weight. Adding more, up to 8-10%, will not make the colour stronger.

What colours and grades are available?

• The most common types are Red Iron Oxide (Hematite/Fe₂O₃), Black Iron Oxide, and Yellow Iron Oxide.
• Grades range from standard powders used in concrete and mortar to high-purity options for cosmetics and ceramics.

Available oxide colours include the following:

Yellow 920 Iron Oxide, Black 330 Iron Oxide, Dark Brown 686 Iron Oxide, White Titanium Oxide, Bright Red 110 Iron Oxide, Light Brown 610 Iron Oxide, Medium Red 130 Oxide, Burnt Umber 656 Oxide, Deep Red Oxide 222, Buff Hitox 9902 Off-white (cream) Oxide, Marigold 960 Iron Oxide, Terracotta 965C Oxide, Chrome Green Oxide, Ultramarine Blue Oxide, Jet Black 360 Iron Oxide, and Cobalt Blue Iron Oxide.

How to mix oxide for colouring?

To find the right iron oxide mixing ratio for concrete, plaster, or mortar, follow these steps:

1. Use the table below to calculate how much oxide you need, based on 4% of the cement’s weight.
2. Mix the oxide well with the aggregate or sand and half of the water. Next, add the cement and the remaining water, and mix thoroughly so the colour spreads evenly.
3. Ensure all batches are identical to maintain consistent colour. Ideally, approve a sample before starting the project.

Tinting strength of oxide pigments

Not all pigment brands are the same. Two pigments that look alike can produce very different results. The key factor when choosing a pigment for concrete is its tinting strength, which affects how deep the colour will be. Making a sample mix under real conditions is the best way to see how a pigment performs.

The natural colour of the cement and its colour effect

When you colour concrete, the cement paste gets coloured, not the aggregate itself. This colored paste coats each piece of aggregate. If you add more aggregate, the colour becomes less intense because the colored paste is spread thinner.

Grey tones tend to dull all colours. As a result, concrete made with standard grey cement cannot be coloured as brightly as concrete made with white cement.

The improvement in colour purity from using white cement depends on the pigment you use. For black pigment, there is almost no difference between white and grey cement. The difference is small for dark brown, red, and burnt umber, but much greater for yellow, marigold, green, and blue.

Pigment loading and colour effect

As you add more pigment, the colour gets stronger until it reaches a saturation point. Adding more pigment after this does not make the colour much deeper and can weaken the concrete.
The saturation point is usually between 5% and 8% of the cement’s weight in the mix. However, you can get a good colour depth with our Oxides at just 4%.

Standard ready-mix concrete uses six 40kg bags of cement per cubic meter. Using 4% pigment means adding about 9kg of oxide. Mortar has more cement, so it needs more pigment. Always base the pigment amount on the cement content only. As a general rule, use about 1.5kg of oxide for each 40kg bag of cement.

Blending of Oxides for Different Colour Shades

Oxides: You can mix oxides together, just like paints, to create different colours. When making colored concrete onsite, add the ingredients to the mixer in the right order so the pigments spread evenly. For powdered colours, start by adding the pigments, then the aggregates, and about half the needed water. Mix well for an even colour, then add the cement and the remaining water until you reach the right consistency.