FCICA News: Hydrostatic Pressure = Concrete Moisture Problems, Or Does it?
Those of you who have read Christopher's columns here in FCI and National Floor Trends know he is a stickler for the correct use of floor covering terminology. One of those misused terms is "hydrostatic pressure." This term is often used to mean any type of a moisture problem on a concrete slab, much like "linoleum" is used to mean any type of sheet resilient floor covering.
As often as the term is used, "Floor moisture problems due to true hydrostatic pressure are rare" says Howard Kanare in his book "Concrete Floors and Moisture." Moisture vapor emissions from a concrete slab can come from a variety of sources and one of them is hydrostatic pressure, which is when there is a column of water higher than the concrete slab). This can only happen in a slab that is below grade level. "Hydrostatic Pressure cannot develop naturally in a slab on grade," Kanare goes on to say, "but it can exist if a slab is fully or partially below grade." Only the section of concrete that is below-grade can experience hydrostatic pressure. It is important to note that hydrostatic means the concrete must be below the water line and not necessarily the soil line. When a pipe breaks under a slab, this is a considered hydraulic pressure and will only be a problem in poor drainage and/or low-permeable soil conditions. An on-grade slab in an area with a high water table would not be classified as hydrostatic.
Most flooring problems are related to, or an indirect result of; moisture vapor emission rate (MVER) conditions, not hydrostatic pressure. The industry standard, ASTM F 710 Standard Practice for Preparing Concrete Floors to Receive Resilient Flooring states, "All concrete slabs shall be tested for moisture regardless of age or grade level." Proper testing is the only way to know about moisture problems before the floor is installed. It is important that our industry understands both the condition and proper terminology for improved understanding and communication. FCICA is glad to be a part of this communication and we thank Floor Covering Installer for providing this space.