Pumping of fines from the foundation layer is a major cause of loss of support beneath Jointed Plain Concrete Pavement (JPCP). The loss of support causes large deflections and slab stresses, which in turn, lead to faulting of joints, corner breaks/diagonal cracks, and finally complete break-up of slabs. This paper describes the experience of the Kansas Department of Transportation (KDOT) wtih undersealing of concrete pavements. Dynaflect deflection tests have been used in two projects for void detection as well as for assessment of effectiveness, while Falling Weight Deflectometer (FWD) tests have been used on one project in 1992.