What happens if the surface of a material dries too quickly?

When the surface of a material dries too quickly, it can create a barrier that slows down the movement of moisture from the interior of the material to the surface. This phenomenon is often referred to as "case hardening." Essentially, as the exterior layer dries and hardens, it can trap moisture inside, preventing it from evaporating effectively. This situation hinders the overall drying process, as the moisture trapped within must find a way to escape through the now-dry, hardened outer layer. Therefore, the correct choice highlights the critical impact that surface drying rates can have on moisture movement within materials during the drying process.