Moisture Migration through Concrete Floor Slabs

Moisture migration through concrete floor slabs can cause damage to floor coverings such as carpet, vinyl, and hardwood. In most cases, the moisture traveling through the concrete floor slab contains dissolved salts. As the water evaporates at the slab surface the salts form a crystalline deposit, which can also attack the floor covering. One common form of moisture migration through floor slabs is by capillary action. The results of this study show that the type and gradation of the material placed below the concrete floor slab is much more important than the thickness of the layer in preventing capillary rise through concrete. Although sand is sometimes used as a capillary break, the results indicate superior performance for open‐graded 3/4 in. (1.9 cm) gravel. Slab cracks in concrete floors can act as major pathways for rising dampness. Tests on the cracked concrete core had higher vapor flow rates than tests on an intact concrete core.