New technologies are paving the way for the comeback of a once-dated decorative concrete application. Exposed aggregate is turning up in prestigious places like the renovation of the Getty Museum in Malibu, Calif., and is adding a touch of glamour to formerly blah driveway, patio, pool deck, or spa areas.
This renewed attention is due to new products and systems that extend the life span of these surfaces. In the past, vintage exposed aggregate driveways were thought of as boring and even unsightly, with uneven surfaces and stones that popped out too frequently. Installers told homeowners to expect exposed aggregate concrete to lose its decorative stones over time. But thanks to longer-lasting products, exposed aggregate finishes now are seen as a beautiful and durable architectural paving option that includes patterned reveals, multiple stones, and a variety of finishes.
A Los Angeles exposed aggregate driveway uses stones 1/2 inch to 2 inches in diameter in a desert brown color. The star pattern achieves textural change by placing the contrasting stones on end. The wide range of stone to choose from–quartz, marble, granite, feldspar, basalt, and obsidian, to name a few–means the design opportunities are endless. Add to this the choice of white or colored cement and specialty seeded materials such as marble, shells, or glass, and clients sometimes have a hard time deciding where to start.
For most contractors, the first step is to connect with a nearby quarry, because specing local stone helps cut down on delivery costs. Chris Fister, owner of Fister Quarry in Batavia, Ill., carries special sands, aggregates, and pigment. "Contractors tell us what they hope to achieve, and we send rock samples to let them develop a mix design," says Fister.
An exposed aggregate driveway in the mountains of Colorado includes a hydronic snowmelt system. This photo, taken after 10 winters, shows a rock-solid surface. The aggregate was trucked in; its color was chosen to coordinate with the stone veneer of the house.Colorado Hardscapes
Before beginning an exposed aggregate project, it's important to carefully select the types of raw materials for the mix design. If there isn't enough cement paste, for instance, you can get aggregate popouts. If the cement content is too high, it's harder to achieve the desired aggregate exposure.
For the popular multiple-stone look, plan to seed the surface. "The key is to get a good matrix surrounding the seeded material," says Byron A. Klemaske II, executive vice president of T.B. Penick & Sons in San Diego. "Most people put rock into the surface and pound it down. You need to slowly but surely work the matrix up around the rock. Be meticulous, and do not pour too much at a time."
When it comes to the reveal, designers specify different depths of exposure depending on the installation's purpose and style. Some require low depth reveals to expose sand particle sizes for a slip-resistant surface. Others call for removing enough material to see a 1-1/2-inch aggregate for a visual punch. Because of the range, manufacturers make retarding admixtures for light, medium, or deep exposures. Choose the retarding agent according to the amount of exposure desired.
Polishing the same materials changes the texture in the cast-in-place outdoor kitchen seat walls and cook surfaces–it also adds formality to those areas while providing utilitarian cook surfaces and seating areas that are different from the floor.Colorado Hardscapes Lance Boyer, president of Trademark Concrete Systems in Ventura, Calif., often uses a brick-red Arizona rock to top seed exposed aggregate. Although there are a number of retarding admixtures on the market, his choice is Grace's Topcast, with 13 different profiles to expose concrete. The mix often includes integral color, and Boyer seeds surface aggregates that range from 3/8 to 1 inch in diameter.
"Architects like the sand finish," says Boyer. "Designers are looking for decorative concrete to look more like natural concrete." For smaller reveals, Boyer typically seeds with 3/8-inch to 1/2-inch stone, saying that it stays in the concrete.
A separate seating area by a water feature uses a concentration of blue and clear glass that mirrors the water coming from the fountain.T.B. Penick and Sons To reduce installation headaches, some contractors recommend Lithocrete Architectural Paving, a patented monolithic paving system that employs small-sized surface seeded materials such as granite, glass, marble, seashells, and other aggregates. Homeowners like the way the crushed materials reflect tiny amounts of light while retaining color integrity. This process is more costly than traditionally exposed aggregate applications, but Lithocrete installers say they are competitive with veneers or real stone.
"The Lithocrete specification weeds out less-qualified bidders, and the finishes are 100 percent consistent," says Neil Hadley, senior associate at Spurlock Poirier, a San Diego landscape architectural firm that specifies Lithocrete when the budget allows.
Designers and homeowners will continue to help make exposed aggregate the comeback kid of the concrete industry, bringing its application inside the home for stamped concrete treatments, concrete countertops, and flooring.
–This story originally appeared in Residential Concrete magazine.
LithocreteColorado Hardscapes Lithocrete. For exterior and interior applications, the Lithocrete architectural concrete paving system offers a wide variety of aggregate shapes, colors, and sizes. The company's creative team works with designers and builders to select the right combination of materials for each job. 949-642-3474. www.lithocrete.com.
LithocreteT.B. Penick and Sons Lithocrete. Combinations of sliced geodes, recycled glass, and Byzantine glass were used in this Lithocrete application. The intent was to create a visual explosion of materials on the concrete surface. 949-642-3474. www.lithocrete.com.