Concrete Surface Retarders For Exposed Aggregate

Concrete Surface Retarder is a spray applied chemical surface retarder that delays the set of the surface of concrete to create exposed aggregate finishes. Surface Retarder is often a water soluble, easily sprayable, non-flammable liquid and should be V.O.C. compliant

Set retarders are an economical, easy-to-use method for producing beautiful exposed aggregate concrete flatwork with consistent results. Many are available in various strengths:

When applied to a freshly placed concrete slab, a surface retarder temporarily halts the set of the portland cement at the surface while the concrete below the surface cures normally.

After the concrete has sufficiently cured the surface of concrete can then be washed or brushed away, exposing the aggregate.

Here are the steps to creating an exposed aggregate finish.

First is Surface Preparation: Place and level and finish the concrete. Do not overwork when closing off the surface or the aggregate will be driven down, and ultimately reducing the depth of exposure.

Second – As soon as the bleed water has disappeared (usually 30 minutes or less), uniformly apply the surface retarder with a pump-up type garden sprayer or paint sprayer, onto the surface of the concrete, try to avoid puddling and overspray.

Third – Cover the concrete with thick mil plastic sheeting, be sure to secure the edges to prevent airflow and ballooning of ther plastic. The main concrete slab will eventually harden, but the surface should remain uncured, it is important to periodically check the concrete. Under normal conditions most retarders will retard the surface for 12-20 hours (read the technical data sheets). With temperatures of 85°F and above, you may need to wash the surface of the concrete the same day.
Fourth – Check a small area to be sure the subsurface concrete has cured sufficiently (usually overnight). Working on one area or section at a time, remove the plastic sheeting and pressure wash the surface to expose the aggregate. it may also be necessary to use a broom or stiff brush to work the surface and help clean the aggregate. On very hot or windy days, after uncovering a section, immediately mist the entire area with water to prevent the surface from flash setting. Then begin washing to expose the aggregate.
Fifth – It is always recommended to seal the surface of the concrete once it has dried. Most sealers will prevent staining and help to highlight the natural color of aggregate. As well as allow you to maintain that ‘just like new’ finish.