New concrete: Attributes that impact chemical staining

If you are in the fortunate circumstance of getting in on project early, you can have a positive influence over the concrete you will be staining.

Concrete mix

Generally speaking, the more cement in the mix, the stronger the reaction you will get from chemical stains, producing more intense

colors. Therefore, use straight cement mixes, such as a five- or six-sack mix or higher, when possible. But be consistent: Staining an area of five-sack mix concrete that adjoins or butts up to an area made with a six-sack mix could cause color variations, despite the use of the same stain color.

Pozzolans and some cement replacements (such as fly ash and granulated blast-furnace slag) can have positive effects on concrete by improving finishability, reducing permeability, reducing efflorescence and minimizing color bleeding. But they also can lessen the reaction between the chemical stain and the concrete surface because removing a percentage of the cement reduces the amount of calcium hydroxide (a reaction product of hydrated lime). Metallic salts in chemical stains react with the calcium hydroxide to produce color.