There are two crucial points leading to air entrapments:
1. Air introduction when mixing:
Air was introduced by mixing the components. This can be caused by choosing the wrong mixer. We recommend using a star-shaped mixer. On the other hand, air may have been introduced by a wrong mixing procedure. It is recommended to leave the stirrer inside the material as close as possible to the bottom of the container. Pulling out the mixer during the mixing process is to be avoided. So the mixer should be pulled out only after standstill.
PU materials are sensitive to moisture. If PU casting compounds come into contact with water or are exposed to very high humidity, the material will foam. The structure of the solid PU’s is then full of air entrapments or foamy. To avoid moisture, the containers should always be kept well closed and stored in a dry place. High humidity should be avoided during processing.