Many building owners and contractors have reported experiencing project delays while waiting for slabs made with lightweight concrete to dry to the moisture-vapor-emission rate typically required by floor-covering manufacturers (3 pounds per 1000 square feet in 24 hours). Though we couldn't find any data regarding the drying time of lightweight concrete, field experience tells us that lightweight concrete takes longer to dry than normal-weight concrete. To help fill this information gap, Concrete Construction devised a testing program to find out how long it takes lightweight concrete to dry.

In test slabs of various thicknesses, lightweight concrete took about 6 months to dry to a moisture-vapor emission rate of 3 lbs/1000 sf/24 hrs. Normal-weight concrete of the same water-cement ratio took only 6 weeks of drying in laboratory air to reach the same level.