Exposed Aggregate Concrete

Exposed aggregate concrete refers to a type of decorative finish in which the cement paste on the surface is washed away to reveal the aggregates in the concrete.


When the concrete gets hard enough, but not too hard, cement on the surface is washed and brushed away to expose the aggregates in the concrete mix.	Close-up of exposed aggregate when it's done. Notice the many different colors of stones. The concrete matrix around the stones has a brown tint thanks to tinted brown sealer.

This is one of the oldest types of decorative concrete that is still widely used today on siewalks, driveways, patios, and porches. A few things have improved with it over the years such as integral coloring and better sealers.

There are three different methods for producing this finish:

Seeding - After the concrete is placed, desired aggregates are seeded or broadcasted onto the surface and worked in with bullfloats or handfloats.
Monolithic - Desired aggregates are mixed into the batch of concrete. This is the most common technique with pea gravel as the usual choice.
Overlay - Aggregates are mixed into a topping material and applied as an overlay. This technique is used on existing concrete that is structurally sound.

The key to a quality finish is getting the cement on the surface to stay soft while everything underneath hardens. This is achieved by using a surface retarder. After the concrete is poured and smoothed out, a retarder is sprayed on the surface. A few to several hours later the cement is washed away with a hose or pressure washer.

Exposed aggregate is a fairly easy method of finishing concrete that anyone with concrete finishing experience can do. Aside from surface retarder, it reqiures no more than the basic finishing tools. There are a few other advantages:

Relatively inexpensive when compared to other decorative methods such as stamping and stenciling.

Provides rugged and slip resistant surface.

Many types and colors of aggregates are available.

Looks nice next to plain concrete making it ideal for borders, bands, and accent designs.

Hides dirt and minor stains.

Easy to maintain.