In the method of exposed aggregate concrete, the contractor adds a mix of gravel, glass chips, or other crushed material to wet concrete, and then reveals this material through a special surface treatment. Landscape designers have used this technique for the better part of a century, and for good reason. Exposed aggregate concrete offers many advantages, including:
- An effective system of permanently marking paths and boundaries in driveways, gardens, and patios
- An easy method for laying non-skid surfaces around swimming pools and hot tubs
- An economical way to create compelling surface texture and design
Architects and designers have used exposed aggregate concrete in domestic outdoor environments such as concrete patios and concrete pool decks, in Minimalist-style factories, and even in post-modern high-rises. Virtually anyone can find a use for exposed aggregate concrete. The basic concepts of exposed aggregate concrete design involve the choice and artful combination of different aggregates.
Choosing the Right Aggregate
In most forms of exposed aggregate concrete, the contractor adds the aggregate during the mixing process, then pours the concrete, and finally reveals the aggregate by sandblasting or power-washing the surface. Since the contractor’s goal is to reveal the texture, color, size and porosity of the aggregate material, the designer’s choice of aggregate is a fundamental decision. Utility is an important aspect of aggregate choice—the aggregate must provide traction and comfort as a walking or driving surface, and it must be compatible with expected conditions of soil and wear. However, the enormous number of aggregate options allows the designer to fully integrate the concrete with a larger architectural vision. Choices such as crushed limestone or manufactured granite chips offer an extended palette of sublime grays that can harmonize with any scheme of building material or housepaint. For a more whimsical effect, the designer can choose saturated colors such as red brick or gold, or opt for a mix of colored glass and polished pebbles.
Exposed Aggregate Concrete Design Possibilities
A thoughtful designer can take advantage of the full range of possibilities offered by exposed aggregate concrete. Different colors and textures enable the designer to easily distinguish walkways from driving paths, or to lay readily visible colored boundaries to aid night-time traffic. A designer might choose to define a safety zone around an outdoor fireplace using brightly colored aggregate, or to delimit outdoor areas such as swimming pools, hot tubs and porches with different textures. Some designers even add areas of smooth concrete, but only in smaller areas, due to its greater propensity for cracking.
Extreme Exposed Aggregate
Some varieties of exposed aggregate concrete deviate considerably from the more common “pour-and-scrub” styles. Ground aggregate concrete is finished by grinding away the top-most layers of hardened concrete. The result is a smooth, polished surface that reveals the character of the aggregate within. The overall effect is regal and imposing, suitable for designs that require a special monumental quality. On the other extreme, hand-laid aggregate concrete has the intimate feel of a handcrafted mosaic. In this technique, the craftsman sets polished stones into wet concrete, creating durable and attractive designs.
With such a wide variety of methods and materials, exposed aggregate concrete can find a place in any design project!