One of the fastest growing markets for iron oxide pigments is in decorative architectural concrete. Iron oxide pigments (IOP) are the lifeblood of decorative concrete and the means for that architectural expression. Only IOP offer the combination of cost effectiveness, light fastness, durability, and cement compatibility that makes colored concrete feasible. Although other types of pigment provide these properties, they do so at a cost several times that of IOP. Even with IOP, the cost of pigment can double the material cost over that of plain concrete, meaning that other pigment types are cost prohibitive for 99% of colored concrete projects.
Products using IOP in decorative concrete fall into five categories:
- Integral color
- Color hardener
- Pigmented release agent
- Pigmented sealer
Integral color is the simpler and easier of the two methods for coloring concrete. Added directly to the concrete mixer, the pigment is dispersed throughout the entire load of concrete by the rotating mix drum, thus coloring the entire concrete element. Pigments can be in the form of powders or water-based dispersions (liquids). Powders often are premeasured into self-disintegrating paper bags so that pigment can be easily and accurately added on the jobsite. Powders also can be added at the ready-mix plant.
Liquids are usually added at the ready-mix plant using automated coloring systems. The advantages of integral color are simplicity and the fact that the entire slab, panel, or structural member becomes the same color. This guarantees that surface damage won't expose gray concrete beneath. The disadvantages to the concrete installer include the higher material cost and additional fees for cleaning out the mix truck—though many ready-mix companies are waiving this charge. The amount of IOP used in a typical 4-inch slab can range from 5 to 25 pounds/100 square feet, depending on the desired color intensity.
The second method that is used to color a slab is using a color hardener, sometimes called dry shake color. A color hardener is a mixture of sand, portland cement, and IOP, which incorporates some troweling aids. This powder is scattered or broadcasted over the surface of the wet soft concrete and troweled in, creating a 1/8-inch-thick colored layer that is denser than the concrete beneath. This denser surface is more abrasion resistant than plain or integrally colored concrete. Color hardener and integral color can be used together for abrasion resistance with solid color. There are disadvantages of color hardener: It is a dusty job for workers and it creates a very thin color layer that can be damaged and can expose the plain concrete underneath. The advantages, however, are lower material costs for most colors and much lower costs for light colors (which requires white cement to produce integral colors). IOP use is on the order of 1 pound per 100 square feet.
For decorative concrete that is stamped to replicate the shape and texture of stone, tile, brick, or wood, a release agent must be applied to the surface to keep the concrete from sticking to the stamping tools. This release agent can be tinted with a contrasting color for a highlighted or antique effect. The application method and usage rate are similar to that of color hardener.
Overlays are thin toppings (1 to 15 mm thick) of polymer-modified colored grouts that are applied over existing concrete. These toppings can be textured in a variety of ways to resemble other materials, similarly to stamped concrete. Some overlays can be stamped with regular stamping tools. IOP usage is slightly higher than that of color hardeners.
Similar to paints, pigmented sealers completely change the color of the concrete surface. Pigmented sealers can be applied over uncured (less than 28-day-old) concrete while paint has to be applied over cured concrete. IOP usage rate is similar to high-end paints.
The market for iron oxide pigments for decorative concrete applications is growing rapidly. Providing a consistent, cost-effective pigment, though, is only the beginning. This market is service intensive and requires considerable technical expertise in both color and concrete. Also, the market is highly fragmented and intensely competitive—many of the 144 decorative exhibitors at World of Concrete are pigment suppliers.
Larry Good has been professionally involved with color in products for more the 20 years including textiles, coatings, and adhesives. The last seven years have been devoted exclusively to concrete.