Surface voids

What are surface voids?

With upcoming trends like industrial living, producers of (precast) concrete had to set a new level of finishing to the concrete... a smooth concrete surface without surface voids. These surface voids, also called air bubbles or pinholes are small holes that have an undesirable effect on the concrete surface. In extreme cases we speak about blowholes and not from air bubbles.

It's understandable that this is one of the biggest challenges in the concrete precast industry. 

What are the causes?

These imperfections to the concrete have a variety of causes, but are most common due to entrapped air, the result of the release agents used in production or excess water in the concrete mix. 

When air becomes trapped within the concrete mix, it can create air bubbles or blowholes in the concrete. Air does not mix with water and cannot get out of the concrete mixture, resulting in voids on your concrete surface. 

The same issue can occur when you have excess water in your concrete mix, mostly caused by a concrete with a higher water-cement ratio. The water does not evaporate enough during curing and remains trapped, leaving holes in the concrete surface. 

Each release agent from Schepens Company has been developed for a specific type of application(s). Using a release agent for an application other than that for which it was designed for or when it is not applied correctly can produce poor results. The lower parts of the molds can become puddles of release agent, causing holes in the concrete surface.  You can count on our experienced team of technical sales engineers and lab technicians to guide you in choosing the right release agent for your application and production method.

Concrete precasting isn't an exact science and there are many variables that have an influence. However surface voids can be minimized. To improve your chance of succes we offer you following tips and tricks:

  1. Break up the air and water in the process by extending the mixing time
  2. Ensure the correct viscosity of the mixture
  3. Use vibration techniques
  4. Use a more uniform aggregate
  5. Use the correct manner of placement (slowing down pouring, tremie pipe,...)
  6. Use a release agent developed for your specific application
  7. Apply the release agent in a correct manner