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Piecing It Together No. 2 subbase material should be spread in minimum 6-inch-thick lifts and compacted with a static roller. Compacting is easier when all stone surfaces are moist. At least four passes should be made. The roller is often in vibratory mode for the first few passes and then static mode for the final passes. This compaction method applies to the No. 57 layer as well, which can be spread and compacted as one 4-inch-lift. If the base surfaces are disturbed, they should be re-leveled and re-compacted. The objective is to have no visible movement in the stone during the last compactor pass and no crushing of the stone. The surface should then be covered with a 2-inch-thick layer of moist No. 8 crushed stone. This layer of finer crushed stone is screeded and leveled over the No. 57 base. No. 8 stone should not be compacted at this point. The surface tolerance of the screeded No. 8 material should be ±3/8 inches over 10 feet. Concrete pavers should be placed immediately after the No. 8 base bedding is placed and screed- ed. After placement, the paver joints are filled with No. 8 stone and compacted with a minimum 5,000-lbf plate compactor, which pushes the No. 8 stone into the upper portion of the No. 57 stone base. Finishing Touches A vacuum sweeper can be used to remove encrusted sediment, leaves, grass clippings, and clogged void materials. Vacuum and sweeper settings may require adjustments to prevent uptake of aggregate from the voids and joints. Additional void materials can be added by mechanically or manually sweeping but it is not recommended to use pressure washers on open-jointed systems. The Americans with Disabilities Act requires that surfaces in pedestrian access routes be firm, stable and slip-resistant. Openings should readily accommodate persons traveling with wheeled mobility devices. When designed properly, PICP installations can meet ADA requirements and can be painted to indicate pedestrian routes. For more information: • ASTM D448 Standard Classification for Sizes of Aggregate for Road & Bridge Restoration • ASTM C936 Solid Concrete Interlocking Paving Units • ASTM C1645 Freeze Thaw and De-icing Salt Durability of Solid Interlocking Paving Units • Guide specifications for Willow Creek permeable pavers are available at www.willowcreekpavingstones.com/permeable-systems . Above: In Farmville, Va., an impervious asphalt parking lot with an existing drainage problem was torn out and Eagle Bay Commercial installed 19,300 square feet of Filterra® BioPave™ pavers that cover the entire parking lot, and three bioretention units, which together now treat water from 1.22 acres or 53,143 square feet. The work took about 11 days total. Left: Permeable pavers can be integrated with other stormwater BMPs as well. The parking lot at Fish Lake sloped toward the lake, so asphalt driving aisles and curb cuts were located between each parking pad to allow sheeted runoff to flow to each pad where infiltration can occur again before eventually reaching a retention basin. Also, a drain system with perforated pipe was installed under the pervious pavement. Sedona was the color of choice for the parking pads and slate for the soldier course. 20 LC DBM DBM LC