Concrete surface retarder
There are various methods of exposing the aggregate in concrete slabs and floors to create a decorative finish. However, the easiest and most reliable technique is to use a concrete surface retarder.
Not only is this method safer and less labour intensive than acid etching and abrasive blasting, it also achieves more uniform results, leaving the aggregate evenly exposed with no fracturing, dislodging, or color loss. What’s more, a surface retarder will give you greater control over the depth of exposure, allowing you to achieve the desired finish. If you’ve never used a surface retarder before, here are some basics to help get you started.
How to use concrete surface retarders
Surface retarders, also called surface “deactivators,” are applied to fresh concrete to chemically delay the set of the surface mortar. Unlike concrete set retarders, they allow the rest of the concrete to cure normally, without affecting the setting rate or strength gain.
Because surface retarders work by stopping the hydration process down to a controlled depth, the underlying concrete will harden properly while allowing easy removal of the surface paste later.
The best time to apply surface retarder is after you’ve completed all finishing operations and the bleedwater has dissipated. Don’t seal the concrete first or apply curing compounds, which could prevent the retarder from doing its job.
Apply surface retarder evenly over the surface using a low-pressure sprayer or roller. Many surface retarders are designed to form a film over the surface that acts as a temporary curing agent and protects the concrete from light rain and wind. However, if extreme wind or rain is expected, you should protect the surface with plastic sheeting.
Tip: The most important issue when applying surface retarder is to ensure complete, even coverage. An easy way to visually monitor where you’ve sprayed is to use a pigmented surface retarder, which contains a tracer dye that allows you to see your progress. The dye will decompose in time after drying.