Q: We have a continuing problem with bugholes (surface air voids) in concrete walls. We have tried many different vibrating techniques but haven't eliminated the problem. Is this just something that we have to live with?
A.: Committee 309 of the American Concrete Institute (ACI) gives the following advice for reducing the size and number of surface air voids in walls.
- Don't use sticky, oversanded concrete mixes.
- Avoid high viscosity form coatings or coatings that are applied in thick layers. They tend to hold air and water bubbles.
- Reduce the distance between internal vibrator insertions and leave the vibrator in the concrete longer.
- Make a row of vibrator insertions as close to the form as possible, but without touching the form.
- Where appearance of the concrete is very important, hand spading next to the form may be helpful.