Colored concrete requires a little more attention to detail than uncolored flatwork. Many faults and blemishes that would otherwise go unnoticed become more prominent or problematic with colored concrete. For this reason, it is vital to maintain best practices when placing and finishing integrally colored concrete.
Before you start the job, it is important to set expectations. Educate your customer – the homeowner, architect, general contractor, etc. – about the characteristics and limitations of integrally colored concrete. Make them fully aware that color is affected by a number of factors including materials used, finishing techniques, and jobsite conditions. Create jobsite mock-ups using the same materials and techniques you would use on the final project to show your customer what they can expect. Final color doesn’t always match the color card exactly, so a mock-up is your ace in the hole.
Communication with your ready-mix producer is key to a successful pour with integral color. Admixtures, water content, and cement content all influence final color. Even if your producer is not adding the color (you may have purchased your own dry or granular color to add at the jobsite; some large projects may use jobsite color dispensers as well), what they do has an effect. They should always be aware that color is going in that load. Higher water to cement ratio will lighten the color. Calcium chloride accelerators cause discoloration. The use of reclaimed aggregates or slurry water is not recommended. Always check admixture compatibility by using the same admixture(s) in the mock-up and final job.
Finishing techniques also have a significant effect on the appearance of color. For example, a colored concrete surface that has been burnished with a power trowel will have more noticeable dark spots or “burns.” Smaller hand tools, which allow the finisher to place more concentrated pressure on the surface, tend to darken the color, too. Naturally different finishes – broom, hard trowel, etc.- will also affect the final appearance of color.
Surface water is yet another factor that impacts the color of the concrete surface. It is generally good practice to avoid troweling bleed water into the surface or sprinkling water as a finishing aid. Anything that introduces additional moisture to the surface of the concrete can lighten or bleach the color, as well as weaken the surface and cause crazing and cracking. Consider using DAY1 as a finishing aid, especially on colored concrete, as it will have none of these negative effects while improving finishability.
With a few extra steps, integral color comes out beautifully. Carefully mange water content, use consistent finishing techniques, and be aware of admixtures’ effects. Do not use water as a finishing aid and avoid excessive bleed water. Take these simple precautions, and your next job featuring integral color will serve you well.