Paver Patio Installation: Open Grade Base, Edging and Poly Sand

How deep do you have to dig for a paver patio that stays flat? In this installation of a 20 by 14 ft patio, 280 square feet in all, the answer was a minimum of nine inches, and the crew went to about ten. The pavers are Techo-Bloc, laid on what the installer calls an open grade base.

Setting the height and digging

The finished height was set by the house: just under the door, at the threshold and fascia plate. From there the excavation had to go down at least nine inches. That depth holds a 6 in. base, 1 in. of paver bedding and the pavers, which are about 2 3/8 in. thick and settle a little into the bedding stone. He prefers bases closer to seven or eight inches, so the dig went to about 10 inches total.

Fabric and base stone

Woven geo fabric goes down first and is stapled in place. Overlaps should be at least six inches; this crew usually overlaps about 12 inches.

The base is 3/4 in. clean stone, meaning it has no fine material and is angular. It goes in two lifts. The first, about three or four inches, is spread with the excavator and raked level, then compacted: the compactor passes about three times left and right, up and down, and diagonally, and a hand tamper handles the edges.

He calls the second lift the more crucial one because the height must be right. It should finish within about two and a half inches of the final paver grade. The crew checks pitch with a level, a grade rod and a laser level, and here the surface was pitched toward the corner where the excavator sat. It is compacted in the same three directions.

Bedding and laying

The bedding is 3/8 in. chip stone. He describes two kinds of base: the open grade used here, and the conventional method of 3/4 in. modified stone with concrete sand.

Pipes are laid on the base, leveled and pitched correctly. Chip stone is dumped over them and screeded with a level, working down the patio. The pipes are then pulled, the grooves filled by hand or shovel, and the area smoothed with a magnesium float, which he keeps beside him while laying pavers so any lumpy or low spot gets smoothed as he goes. He says two people can lay a patio this size, just over two pallets of pavers, in a day.

Edging, compaction and poly sand

Edging strips are fixed with 10 in. or 12 in. spikes every foot. After the edging is in, the first compaction pushes the pavers slightly into the chip stone. Polymeric sand is then brushed in to fill the joints to the top, and the compactor runs over the pavers again so the sand reaches the bottom of the joints. More sand is swept in up to the beveled edge of the pavers.

Excess is swept off and lightly blown away before activation, since the sand is activated by spraying with water. The last step is backfilling the edges.