Pigments for Coloring Cement Based Products

When most people think of concrete buildings, their reaction is of a cold, sterile environment. Often people try to change this feeling by painting these buildings. However, a more durable, long lasting solution is to color the cement itself. The pictures above, of Frank Lloyd Wrights's Gugenhiem Museum, illustrate the effect color can have on a building.

Products manufactured from colored concrete are being used more and more in today's construction. Colored concrete was originally used solely as an inexpensive substitute for natural stone. Today, architects and builders frequently use colored concrete, due to its flexibility in both color and texture, to tackle their design problems. For example, lighter colors can be used in sunny climates to help reduce heat absorption and glare. The opposite can be used in colder climates where a darker color can promote more rapid melting of snow and ice by increasing the building’s heat storage capability. Changes in either the texture or color of an exterior can also be used to create visual interest.

So how does this work?

 Colored concrete products are normally made up of cement, pigment, sand and aggregate. Of these materials, pigment particles have the smallest particle size and the greatest surface area. As a result of this high surface area they reflect the most amount of light, giving the product its colored appearance. The more pigment that is added to the concrete product, the more the concrete product's color changes. By adding a small percentage of pigment, a slight color shading can be achieved. A larger pigment addition can bring about a larger change in color.

 It is important to select the right pigment when coloring concrete based products. Not only should the pigment comply with ASTM C979, but it should also be purchased from a supplier who can demonstrate their ability to supply consistent color.

 The human eye can differentiate between one and two million different color shades. With the eye so sensitive to color changes, the color manufacturer's job is to provide a tight range of color variation in their products. In order to ensure that the color has limited variability, the color industry has developed sophisticated instrumentation for measuring color. We have all seen white light broken down into a rainbow of colors using a prism. Color itself is the percentage of a given wavelength of light that is reflected into the eye of the observer. But we see color in what is called an opponent color system. We save approximately 200 internal color references of the millions of shades that the eye can separate and we compare the observed color with the reference. We do this by breaking the color down into three components:

        Is the color lighter or darker than our reference?
        Does it have more of a red shade or green shade than our reference?
        Does it have more of a yellow shade or blue shade than our reference?

Hoover Color uses a computerized color measuring system to measure these color variations and publishes this information to its customers in a "Certificate of Analysis." This helps to ensure that the color variation is within previously stated specifications..

When pigments are added to a concrete mix, care should be given to ensuring a consistent pigment-to-cement ratio. While sand and aggregates influence the color of the final product, the pigment and cement are the most important constitutes in the colored mix. In actuality, the color of the cement acts as an additional coloring agent. The lighter and whiter the cement, the brighter the final color of the cement product.

Pigments can be added up to a 15% pigment-to-cement ratio without seriously affecting the strength of the final cement. However, pigment loadings at this level are normally not cost efficient since the pigments exhibit diminishing increases in intensity as loading gets higher.

Site Last Modified On:  October 21, 2002.

©Copyright Hoover Color Corporation, 2001.