Pouring and Finishing an Exposed Aggregate Walkway
By Larry Walton
One of my favorite home projects is building a new concrete walkway. It could be because I grew up on the west side of the Coast Range in Oregon where rainfall can reach 200 inches in a year. With conditions like these, it doesn’t take many foot falls for sod to become mud. Whether you are walking around the garage to roll the trash bins out to the street or you’re headed out to the green house, you’ll have an appreciation for a new concrete walkway.
Anytime you do concrete work you have the privilege of choosing the type of finish the new concrete will have. Exposed aggregate can be a good choice, especially if you are matching existing concrete or making a purposeful contrast to another finished surface.
Aggregate is the sand and gravel part of the concrete mix. It’s what the cement bonds to, and it gives the concrete substance and strength. Smooth, stamped or broomed concrete hides the larger pieces of gravel below the surface. The exposed aggregate method removes the top fine layer so individual gravel pieces are visible on the surface.
With the exception of the concrete mix you order, the setup for exposed aggregate is the same as with other finishes. “There’s nothing in particular you have to do, whether it’s broomed, stamped or exposed,” says Matt Villers of Washington-based Concrete Specialties Inc. (CSI). All of the standard concrete walkway steps apply.
Anytime you are building a walkway, consider the lay of the land and how water will run off. For proper drainage you’ll need a 1/4 inch of fall for every foot of walkway. For example, one side of a 4-foot wide walk should be 1 inch lower than the other side in the direction that carries water away from any structures. Most of the time water will drain into a lawn, flower bed or driveway.
Unless code requirements dictate otherwise, walkways should have 3-1/2 inches of compacted rock base under 3-1/2 inches of concrete. This thickness means you can use 2-by-4s for form boards. You may wish to use 2-by-6 form boards to produce a 5-1/2-inch thick walkway section for areas that will be driven on, such as where the walkway intersects a driveway.