Mismatching colors between two slabs that are integrally colored presents quite a challenge for many contractors. With multiple loads pours the colour variations tend to become more noticeable with some slabs even appearing a shade or even two darker than the previous one. The differences in construction joints tend to become more noticeable on cured and sealed concrete as compared to when it is being placed wet.
Achievement of a uniform colour is based on the consistency in the variables used during the order. Factors such as design of concrete mix, water to cement ratio as well as a constant supplier of cement are considerations to put in place for a uniform colour. With other variables ranging to the weather, finishing practices, and even the relative content of moisture in the sub grade some factors are beyond the supplier of the ready mix. A shade line between slabs can actually be gotten from presence of trees or even houses depending on whether it was cloudy or sunny when the mixture was cured. With different liquid finishing aids such as water or solvents used in one mixture and not the next, a difference in the colour is likely to be achieved. Floating, trowel ling, stamping or even brooming concrete in different setting stages will eventually cause a colour differentiation.
Use of a colour hardener when integrating colors before setting the mixture allows for one to ensure a constant colour is maintained. With one slab butting on another the color difference is actually very apparent. With this in mind a hardener is dusted with matching colors on the slab at the header board area and gradually fading it into the integral colour. At the connecting points where the difference is much noticeable applying the colour hardener along with the integral colour makes it unnoticeable. An antiquing release agent in powder form is used hence cohesive appearance that is also speckled is used.
Use of borders
Throughout the slab ribbons and borders can be used at the construction joints to combat the differences in colour. When different shades of a colour are butted up against each other, the colour change on the joints becomes unnoticeable. However, the use of a contrasting band in between the joints makes the colour differences even less noticeable with sometimes the differences disappearing altogether. It is necessary to note that it is not all differences between slabs are actually colour differences and a great idea to use band when multiple pours are applied. If you are using stamped or decorative concrete for the first time then read about mismatched colors in stamped & decorative concrete and what’s the best solution to this problem.