Few roots grow into coarse sand and gravel (layer 4) because it holds very little water. Also, this layer absorbs and transmits effluent so quickly that it is not purified by soil organisms. The effluent can then percolate to the ground water and contaminate drinking water supplies.

Sandy loams: 20 percent or less clay and 52 percent or more sand and the percentage of silt plus twice the percentage of clay exceeds 30; or less than 7 percent clay, less than 50 percent silt, and between 43 and 52 percent sand.

Add a layer of builders sand ($4, The Home Depot) on top of the gravel. To calculate the sand depth, subtract your pavers' thickness from 4-1/2 inches. Next, make a second screed by notching a long 2x6 to the depth of the pavers, then level the sand. If the frame's top was set at the appropriate slope, the sand will be at the proper pitch too.