Which moisture entry mechanism is driven by capillary action in porous materials?

• A. Vapour diffusion
• B. Capillary water
• C. Bulk water
• D. Air-transported moisture

Answer: (B)

Capillary action in porous materials drives the movement of liquid water within the pore network. Water wets the pore walls and forms menisci, and the curvature of those menisci creates a capillary pressure that pulls liquid water through narrow pores. This causes capillary water to move through the material, often rising or spreading even when gravity or other forces would not move the liquid. Vapor diffusion involves water in the vapor phase moving through air-filled pores, not liquid pulled by capillary forces. Bulk water is free liquid water flowing due to gravity or hydrostatic pressure, and moisture carried by air relies on air movement rather than capillary suction. Capillary water is the moisture form governed by those capillary forces, especially prominent in fine pores.