Exposed Aggregate Concrete Finish Techniques

Written by erik devaney
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Exposed Aggregate Concrete Finish Techniques
Exposed aggregate concrete has a coarse, rugged finish. (concrete wall image by Lela Obradovic from

Using exposed aggregate concrete finishes can help create driveways, walkways, patios and other outdoor hardscape features that are textural and aesthetically pleasing, as opposed to flat and dull. These finishes display aggregates, or crushed bits of rock and gravel, at their surfaces; and help provide traction in addition to decoration. If you are thinking of using an exposed aggregate finish, there are several techniques available.

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The monolithic technique is the most popular when it comes to installing exposed aggregates. The technique requires that you mix your aggregate materials into a batch of concrete, and then pour the concrete into a form, or framework of support beams, just like you would when installing a standard concrete surface.

According to the concrete resource website All Things Concrete, most people utilise pea gravel as their aggregate when using the monolithic technique. Pea gravel consists of tiny, rounded natural rocks with diameters of between 1/4 and 3/8 inch, as the copper alloy resource guide Copper notes.


Unlike with the monolithic technique, with the overlay exposed aggregate technique you do not create a new concrete structure, but instead you cover over---or resurface---an existing one. According to All Things Concrete, overlaying requires that you mix aggregates into a small batch of concrete, which you then spread over the top of a structurally sound surface.

Using a Chemical Retarder

Whether you are using the monolithic or overlay technique, a chemical retarder is essential for ensuring that your aggregates stick out of the hardened concrete, providing that textural look you desire. After pouring and levelling your concrete, spray the retarder over all of the surfaces you want exposed. The retarder will keep the surface layers of the concrete soft while the layers below it harden. However, as the exposed aggregate resource website Exposed Aggregate Concrete warns, chemical retarders are highly caustic, and misuse can result in the formation of irregular patterns, holes and other blemishes.


Once you apply a chemical retarder, thereby keeping the surface concrete soft, you must gently scrub away some of this concrete so that the aggregates can really stick out. According to the cement and concrete resource Portland Cement Association, for optimal results, use a scrub brush and hose to loosen and wash away the softened concrete. Just make sure not to scrub and spray too hard, otherwise the concrete might not retain enough strength to keep the aggregates stuck in place.


An alternative to using the monolithic or overlay techniques--and then applying a chemical retarder and scrubbing--is to use the seeding technique. Unlike the above-mentioned exposed aggregate strategies, seeding does not require that you mix aggregates into the concrete prior to pouring it. Instead, as All Things Concrete mentions, you broadcast or "sprinkle" your aggregates on top of the concrete as it is hardening.

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