Wouldn't you just know it? Just when you thought negative hydrostatic pressure described the majority of moisture vapor transmission-related flooring problems, some wise-guy expert comes along and says it ain't so. According to Mr. Know-it-All, hydrostatic pressure can cause problems for finish flooring installations only when water is at a level above the flooring surface and exerts upward pressure equal to the depth or “head” of water times its density (62.4 lbs./cu. ft.), or approximately 0.47 psi pressure per foot of water. (Yea, right.) Moisture vapor transmission (aka negative hydrostatic pressure) is nothing compared to true hydrostatic pressure. Hydrostatic pressure can often exert enough physical pressure to lift an entire concrete slab clean out of the ground!