Q.: On some recent small concrete wall jobs, we found small surface air voids, or bugholes, on the surfaces of the hardened concrete. Although the walls seem structurally sound, I'm concerned about their appearance. Is there anything I can do to prevent bugholes from forming?
A.: Bugholes on the surface of concrete walls are usually caused by lack of consolidation at the concrete surface, which can leave air voids trapped next to the form. Sticky or stiff concrete mixes that tend to have low workability and may have an excessive sand or entrapped air content can be harder to consolidate.
To minimize surface air voids, insert the vibrator as close to the form as possible, but without touching the form. Proper vibrator spacing and duration of vibration also result in better consolidation. Avoid using vibrators with too large an amplitude, and completely insert the vibrator head. Also avoid applying high-viscosity form coatings in thick layers that can trap air and water.