Just when you thought you were going to install another exposed aggregate pool deck, your clients inform you they want the concrete to “glow” with stone accents. Don’t hit the panic button if you’ve never worked with a glowing medium before. Glow stones are applied in exposed aggregate finishes in the same way as other decorative aggregates such as sea shells and tumbled recycled glass.
Hand broadcasting is the easiest and most popular application method. Basically, you toss the glow stone over the entire concrete surface as it is setting up. Then you gently work the stones into the curing concrete with a trowel, leaving them just under the surface covered with a thin film of concrete. For general flatwork, ½-inch stones are a good size to use.
Exposing the stone
To get the stones glowing, they must be exposed to light during the day so they can absorb energy to use once the sun sets. Once the stones are embedded, you can expose them in one of two ways:
Chemically: Chemical exposure can be achieved by lightly spraying a concrete retarding agent over curing concrete. The concrete retarder chemically slows down the curing process leaving 1/8 to 3/8 inch of the surface uncured. The top is then pressure-washed off, which exposes the glow stones on the surface and allows them to charge by day and glow at night.
Mechanically: This technique is more labor intensive and requires the use of diamond-laden polishing pads mounted on either handheld polishers or heavy-duty concrete floor polishing machines. The polishers “cut off the top” of the concrete to expose the glow stones. This form of polished, glow-in-the-dark concrete finishing is typically seen in interior applications. However, recently it’s been successfully applied on the interior of concrete pools and spa tubs, creating a beautiful star-like pattern on the bottom.
The key to a glowing success
As a decorative concrete professional, it’s very important to analyze the project’s environment to determine if there are any competing light sources nearby that will shine on the surface once the sun sets. A light source, such as a streetlight or landscape lighting, will affect the overall glow intensity. In some cases, it can neutralize the glow effect altogether.
Before you seed the surface, you should test the stones’ glow effect by placing samples on the ground where the concrete is going to be and having the clients observe them at night. This way, your clients will have an idea of what the glow surface will look like prior to the concrete pour.
Unlike other accent lighting systems that require electricity or batteries to function, high-grade glow stones only need 15-20 minutes of daylight or artificial light to glow all night. The initial brilliance will be like Superman’s Kryptonite and then the glow will begin to diminish throughout the night, remaining at about a 40 percent glow level until the sun rises or the lights come on (interior).
1. Pour concrete mix as you normally would.
2. Bull float the surface.
3. Seed glow stone by hand where you want them.
4. Work the glow stone into the slab with a fresno or regular trowel.
5. Apply a retarder per manufacturer’s instructions.
6. Let concrete set and cure.
7. Wash off the surface with water per retarding agent manufacturer’s instructions.
That’s it. You’re ready to glow!