Is it possible to artificially weather new concrete to match existing surfaces?
A system that has proved satisfactory in industrial locations consists of first washing down the surface with a 10 percent hydrochloric acid solution. This treatment removes the cement skin from the surface. One or more washes with a solution containing a carbon-black pigment should then be applied, with a thorough rinsing with clean water between applications. The concentration of pigment, and the number of applications needed, should be established according to the degree of weathering deemed necessary.