Step 8 – Library of Color Samples
If you’re grinding the surface of the concrete the aggregate will also be an important consideration. As soon as you start grinding into the concrete you’ll expose the fine sand and then the rock aggregates. The aggregate in your concrete will vary depending on the geology of that region. If you’re planning to grind and polish your work, choose a color that looks nice with the aggregate in your area. (Charcoal concrete with white limestone aggregate doesn’t look that nice.)
There are two common types of pigments used in concrete, synthetic oxides and organics. Both are available in two forms, powder and liquid. Organic pigments will break down in UV light, making the colors fade over time. Synthetic oxides (metal rust) will fade less, and all of the pigment we use at CHENG is synthetic. Dry pigments are more economical, but care needs to be taken when using them, especially because the colors can contain elements that are harmful when inhaled. Liquid pigments are dissolved in water, so they’re easier to work with, but the added water makes them heavier and can add to the shipping cost.
Here is a list of the some common colors and the metals that are used to produce them.
White – Titanium Dioxide
Red – Iron
Blue – Cobalt
Green – Chrome
Black – Iron
Using pigments is easy, you just mix everything together, but to get consistent results, you need to know a little bit of math. Color calculations are based off of the weight of the cement (the pigmentable material). A color loading greater than 10% will weaken the concrete.