How much iron oxide to color cement?

Jul. 01, 2024

The Benefits of Tried and True Iron Oxide Pigment

The products and finishes in the decorative industry are becoming more sophisticated &#; polymer-modified toppings, nanotechnology sealers, and sustainable stains and dyes to name a few. These high-end materials and systems are the new &#;buzz&#; in the industry and seemed to dominate the trade-show conversations this past winter season. New technology is great, and I am a big supporter of REAL technological advancements. But at the same time, we all need to remember the old tried-and-true products that still make up a large portion of the industry, and more importantly, refresh ourselves on the fundamentals, the right way to use them.

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As often happens, a recent call started me thinking about this. The person on the other end was asking why their recently poured colored-concrete basement floor was the wrong color, had a white haze over the surface, and was darker on the edges compared to the middle. As I spent the next 10 minutes explaining the cause of each issue, I realized how important the basic products and the fundamentals of their installation are in what we do every day.

When it comes to basic nonglamorous products that still have a huge impact on our industry, you don&#;t have to look much further than iron oxide pigments. The workhorse product that started the decorative concrete industry more than 50 years ago is still the single most-consumed product in our industry today. Also known as integral stain, dye, or just plain color, iron oxide is nothing more than manufactured rust. What makes it such a workhorse and a staple in our industry is that it is the only colorant that can withstand the extreme alkaline environment of concrete without fading or leaching.

Iron oxide particles, as produced for the construction industry, are 10 times finer than cement particles. When added into a concrete mix, the iron oxide particles actually surround and coat the cement particles. This is why integral color is dosed or metered based on the cement content, not on the amount of sand, stone or water. That the average color loading is only 2.5 pounds of pigment per 94 pounds of cement (2.6 percent) demonstrates the coloring power of iron oxide pigments. This coloring power is called tinting strength, and it is important to note that not all iron oxides have the same tinting strengths. Not only do different manufacturing processes affect the tinting strength, but adding inert fillers when blending colors can dilute or reduce the tinting strength of pigments. To ensure you are getting the strongest tinting strength, do your homework and avoid cheap color that contains fillers.

Using excess water will lighten and discolor integrally colored concrete. This is especially true if water is used during the finishing process, which resulted in broom marks and streaks on this concrete slab.

In addition to the basics of what iron oxide pigments are, I think knowing the fundamentals of how they are used and understanding common problems associated with their use are even more important. There are five key components that determine the final color when using iron oxide pigments in concrete.

The pigment: As we discussed previously, using a good quality pigment from a reputable manufacturer is important. Proper blending and color consistency is something you as the installer have little to no control over, so trust in your supplier is important.

Water content: Also known as water-to-cement ratio, this is by far the No. 1 cause of colored concrete issues. The amount of water used to make concrete has a dramatic and permanent effect on the final color. The more water used, the lighter the color. This not only holds true for water used in the mix, but also for any water added to the surface during the finishing process. Use as little water as possible, and consider chemical admixtures (plasticizers, water reducers, etc.) to reduce the amount of water needed. No matter what &#; stay consistent.

Cement content: The next-biggest factor that affects the final color is the cement content. The amount of cement used in a mix is critical because it is what the pigment content is based on. Start changing the amount of cement from batch to batch and you WILL get a color change. The place where most installers get in trouble is dosing by &#;sack mix,&#; not by actual cement weight. Five-sack mix can have actual cement content ranging from 460 pounds to 650 pounds.

Cement color: Probably the most misunderstood and misdiagnosed cause of colored concrete issues is the color of the cement and the impact it has on the final color. While most cement manufacturers strive for overall product consistency, they do not test for color. Tests have found that cement coming from the same plant can have dramatic color variances over a period of weeks and months. If you have long time gaps (weeks or months) between colored pours, it might be worth your time and money to keep cement retains to ensure the color has not changed.

Aggregate color: While aggregate color has little to no direct impact on actual color, it can have an indirect impact on the overall mix. A sand mix will not develop the same color as an aggressive stone mix. Also, consider how aggregate will impact the final color if an exposed aggregate finish is performed.

As with most tried-and-true products and processes, success usually comes down to one tried-and-true guideline. In the case of iron oxide pigments used in integral color, the rule of thumb is &#; stay consistent! Control your environment, control your water, and try to keep everything as consistent as possible. Iron oxide pigments are not going anywhere soon, so the more you understand regarding the basics of how they work, the better off you will be.

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Oxide Powder for Concrete Coloring Over 15 Colours, Buy ...

Oxide powder (pigment) is used as dye or colourant in various applications, including ceramic, paint, concrete, coating, ink, leather, plastic and rubber. This dry pigment powder with an iron oxide base can be mixed with a binder to tint glaze and varnish or make paint.

Iron oxide is used to coat the particles in cement and mortar/plaster. You can achieve a good colour using 4% by weight of oxide to the weight of cement. At 8-10% saturation occurs and no additional benefit is achieved.

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Iron-oxide mixing ratio for concrete/plaster/mortar, follow these steps:

Determain the weight of the cement and use the table below to calculate the amount of oxide to use (based on 4%).
Mix thotoughly with aggregate/sand and 1/2 the water. Mix thoroughly prior to adding cement and remaining water. Adequate mixing must occur to ensure full dispersion of colour.
To achieve consistant colour ensure all batches are identical. Ideally a sample should be approved before undertaking the job.

MIX CEMENT OXIDE READY MIX 1cm3 250kg 10kg SITE MIX 40kg 7kg 280g BAG CONCRETE MIX 25kg 3kg 120g PATCH KIT 1kg 300mg 12g MORTAR 1kg 300mg 12g

The above ratio is an indicative guide. Therefore, you need to determine your own mixing ratio by doing a few tests before proceeding with your job.

Pastel shades can be obtained with the light brown, reds, green and yellow by using white cement instead of grey in the mix.

Tinting strength of pigments

One brand of pigment is not the same as another. Two pigments identical in appearance may have a completely different yield. The decisive property in the use of a pigment for colouring concrete is tinting strength, which determines the depth of colour for various brands of pigment. A sample mix prepared under practical conditions can provide reliable information on this.

Natural colour of the cement and colour effect

In colouring concrete it is not the aggregate that is pigmented, rather the cement paste is coloured, which then forms a layer on the individual aggregate particles. Therefore the more the coloured cement paste is diluted with aggregate, the less intense will be the colour of the concrete.

Grey has a subduing effect on all colours, no matter where they are. Therefore, it is not possible to colour concrete made with normal grey cement as brightly as concrete containing white cement.

The gain in colour purity obtained by using white cement depends, however, on which pigment is added. In the case of black there is virtually no difference between concrete made of white cement and one made of grey cement. With dark brown, red and burnt umber the difference is small while it is considerable with yellow, marigold, green and blue.

Pigment loading and colour effect

With increasing pigment loading, the colour intensity moves towards saturation point. Adding more pigment at this point does not significantly deepen the shade and may affect the structural strength of the concrete.

The saturation point lies between approximately 5% &#; 8% calculated on the weight of the cement in the mix. However a good depth of colour can be achieved at 4% loading with our Oxides.

The normal ready mix concrete strength is 6 x 40kg bags of cement per cubic metre of concrete. 4% of this equates to approximately 9kg of oxide. Mortar on the other hand with its higher cement content requires more pigment. It is important to remember that pigment addition relates to the amount of cement in the mix and nothing else. A rough guide is to use approximately 1.5kg of oxide per 40kg bag of cement.

Blending of Oxides for Different Colour Shades

Oxides, like paints, can be mixed to provide a variety of colours. When mixing coloured concrete onsite, ingredients must be placed into the mixer in sequence to ensure the pigments disperse fully. With powdered colours, put pigments into the mixer along with aggregates and approximately half the required water and mix well to ensure a uniform blend: follow this by adding cement and sufficient water to obtain the desired consistency.