20 days
Without a vapor barrier, the relative humidity in the slab just below the surface can often be 100%. Since the air is seldom that humid, moisture is going to move from the slab into the air and as the surface dries a bit it will draw moisture up from the bottom. Whitening of sealers is often caused by applying it to a wet surface. Typically a relativehumidity of 75% to 80% is targeted for installation offloor coverings. Relative humidity probes can determinethe moisture profile from top to bottom in a slab, condi-tions below the slab, and can monitor the drying of aslab over time, leading to predictions of future moistureconditions. Avoid using curing compounds on floorswhere coverings or coatings will be installed.• Allow sufficient time for the moisture in the slab todry naturally while the floor is under a roof and pro-tected from the elements. Avoid maintenance and clean-ing operations that will wet the concrete floor. A relative humidity of 100% means the air cannot contain any more water vapor at that temperature, whereas a relative humidity of 50% means that the air only has only half as much water vapor as it can hold at the current temperature. These limit how much drying occurs. If your shop is at 100% relative humidity it doesn’t matter how long you “dry” the concrete. It won’t lose moisture and dry out because the air surrounding the concrete can’t hold any more moisture. Remember: wet concrete doesn’t dry out in small, cold shops with still air Dew Point is the air temperature at which the air is saturated with water vapor. Warm air can “hold” more water than cold air. When air at a given temperature can’t hold any more water it is fully saturated and is at 100% relative humidity. The air isn’t holding onto the water vapor. These limit how much drying occurs. If your shop is at 100% relative humidity it doesn’t matter how long you “dry” the concrete. It won’t lose moisture and dry out because the air surrounding the concrete can’t hold any more moisture. Remember: wet concrete doesn’t dry out in small, cold shops with still ai Most of the moisture is usually retained in the concrete and condense due to the dew point which is the temperature at which the water vapour in the air turns into water. What happens is that once the air cools, it get saturated meaning that it cannot hold any more moisture. When drying concrete fails to happen and the floor is damp, applying water based adhesive on it means that it will absorb the moisture from the floor during evaporation changing the moisture content of the adhesive preventing it from curing and becoming permanent. Concrete continues to gain strength after pouring for as long as it retains moisture, but the longer it moist-cures, the slower the rate of strength gain. Moist-curing concrete for 20 days more than doubles its strength compared with four days of moist-curing, which is considered a minimum.  A relative humidity of 100% means the air cannot contain any more water vapor at that temperature, whereas a relative humidity of 50% means that the air only has only half as much water vapor as it can hold at the current temperature. Dew Point is the air temperature at which the air is saturated with water vapor. Warm air can “hold” more water than cold air. When air at a given temperature can’t hold any more water it is fully saturated and is at 100% relative humidity. The air isn’t holding onto the water vapor. These limit how much drying occurs. If your shop is at 100% relative humidity it doesn’t matter how long you “dry” the concrete. It won’t lose moisture and dry out because the air surrounding the concrete can’t hold any more moisture. Remember: wet concrete doesn’t dry out in small, cold shops with still air. Thisreduces the amount of residual moisture in the slab,will require a shorter drying period, and result in alower permeability to vapor transmission. Water re-ducing admixtures can be used to obtain adequateworkability and maintain a low water content. Avoid using curing compounds on floorswhere coverings or coatings will be installed.• Allow sufficient time for the moisture in the slab todry naturally while the floor is under a roof and pro-tected from the elements. Avoid maintenance and clean-ing operations that will wet the concrete floor. CIP 28 - Concrete Slab Moisture WHAT is the Problem?Concrete slab moisture can cause problems with theadhesion of floor-covering material, such as tile, sheetflooring, or carpet and bond-related failures of non-breathable floor coatings. Avoid using curing compounds on floorswhere coverings or coatings will be installed.• Allow sufficient time for the moisture in the slab todry naturally while the floor is under a roof and pro-tected from the elements. Avoid maintenance and clean-ing operations that will wet the concrete floor.
http://www.concretenetwork.com/vapor-barriers/moisture.html http://www.nrmca.org/aboutconcrete/cips/28p.pdf http://www.concretecountertopinstitute.com/temperature-and-relative-humidity-what-they-mean-for-you-and-your-concrete/ http://www.concretecountertopinstitute.com/temperature-and-relative-humidity-what-they-mean-for-you-and-your-concrete/ http://www.disasterrestorationexperts.com/waterdamage/drying-concrete-after-a-flood/ http://articles.sun-sentinel.com/1995-11-03/lifestyle/9511010249_1_septic-system-septic-tank-leaching-field http://www.concretecountertopinstitute.com/blog/tag/curing-practices/ http://www.nrmca.org/aboutconcrete/cips/28p.pdf http://www.nrmca.org/aboutconcrete/cips/28p.pdf
concrete can hold moisture for how long?