Why must the inner surfaces of the concrete mould greased with oil?

The inner surfaces of a concrete mold are greased with oil to create a smooth release surface, preventing the concrete from sticking to the mold when it sets. This lubrication facilitates easier demolding, reducing the risk of damage to the concrete structure and the mold itself. Additionally, it helps to achieve a better surface finish on the concrete by minimizing imperfections that may arise from friction during the removal process.