When the castable refractory linings are installed without drying out sufficiently and exposed to high humidity for a long time, white fibrous or powdery substance appears on the surface, which is called “efflorescence”. The main reason is the cement of castable refractory linings contacts with CO2 and moisture in the atmosphere to form calcium carbonate (CaCO3). In general, efflorescence takes place more readily in lightweight castable refractories. In the walking beam reheating furnace construction project, there are many white powdery substances in the walking beams, because the construction procedure causes poor ventilation in the surrounding area, and the internal moisture of castable refractory linings cannot be evaporated effectively. In future, the project programming should consider the environmental humidity and surrounding ventilation.