Sand set

ICPI's glossary defines interlocking concrete pavement by its build order: hand-sized concrete units, placed in an interlocking pattern, compacted into coarse bedding sand, the joints then filled with sand and compacted a second time to create the interlock.

The bedding layer itself is specific: in non-permeable applications ICPI calls for a nominal 1 inch layer of natural or manufactured sand conforming to ASTM C33 or CSA A23.1, the two standards ICPI's glossary names. That 1 inch layer sits on the paver base below it, the structural layer that supports the units and the bedding.

ICPI defines joint sand plainly: sand swept into the openings between the units in non-permeable applications. It is the last material in the build order, and it is also the part of a finished sand-set surface most exposed to what happens above it.

Because ICPI's build order gets the structural interlock from sand-filled, compacted joints, that sand is the part of a finished surface a rinse has to leave in place. Whether a cleaning can wash it out is answered directly on can paver cleaning damage the joints, and what heavy rain does to it is covered under joint sand and the Naples rain. The same joint sand comes up again when weighing an installer's no-seal advice.

The Brick Industry Association's clay-paver terms map onto the same system. Its Technical Note for sand-set clay paving describes flexible, mortarless paving on a sand setting bed, and such pavers can go over a flexible or rigid base, including aggregate, asphalt, cement-treated aggregate or concrete.

BIA is specific that Type F clay pavers are intended to be set in a sand setting bed with sand-filled joints, the flexible counterpart to the rigid, mortar-set system its Type R pavers are made for instead. Which type a given clay surface was built with is a question for whoever installed it.