Masonry walls that leak create problems for contractors, architects, and owners. Water that passes through exterior walls can damage interior wall finishes, floor coverings, ceilings, and building contents. Water that penetrates only the exterior face can cause staining, corrosion, organic decay, efflorescence, and freeze-thaw spalling. Therefore, any water that enters a masonry system can cause damage. Possible leak paths in the wall surface include the brick, mortar, and the brick/mortar interface. Cracks and voids at the interface between the brick and mortar provide the most common pathway for rainwater to enter a masonry wall. Much less water penetrates through the units and mortar than enters through the unit/mortar interface. Three methods of measuring water penetration in masonry are the ASTM E 514 pressure chamber test, the permeability test, and the low-pressure tube test. (The low-pressure tube is also called the RILEM tube, masonry absorption test or MAT tube, or Kartens tube.)