Even with the best materials and equipment, operated by skilled professionals and to the highest standards, the designs of some aluminium castings can be prone to slight imperfections within the cast parts.
Shrinkage can result in sponge porosity, which can result in occasional issues with leakage through the casting walls. To prevent this, a process called vacuum impregnation can be used to seal the castings.
A commonly used practice in automotive castings, it is becoming more popular within general castings to eliminate the need for 100% pressure testing of parts. The resin used with the process is introduced under pressure and once cured forms a solid seal unaffected by petrochemicals.