Exposed aggregate shows the stone inside the concrete instead of the gray cement paste on top. HomeGuide describes two methods: mixing decorative aggregate into the batch, or seeding stone onto the surface of a fresh slab. Either way, a surface retarder slows the top layer from setting, and the paste is washed off to reveal the stone. Options range from crushed stone to white or river pebbles, basalt and quartzite.
The finished surface is textured and slip-resistant, which is why people choose it for pool surrounds, sloped walks and driveways that see frost. HomeGuide puts exposed aggregate at $7 to $18 per square foot installed nationally, roughly $2 to $3 more per square foot than plain concrete, with a typical patio at $2,800 to $7,200.