Paver base

ICPI's glossary places the base beneath the pavers and their sand-set bedding, and above the subgrade, or above a subbase where one is used. Its stated purpose is to structurally support both the paving units and the bedding materials over it.

Nothing about the base is a single material: ICPI defines it as open-graded or dense-graded aggregate, with or without Portland cement or asphalt treatment, or as asphalt or concrete outright. What holds across every option is its job, structural support, placed at a thickness the design calls for before the sand and pavers ever go down.

ICPI's construction guide gives minimum compacted base thicknesses over well-drained soils: 4 inches for sidewalks, patios and pedestrian areas, and at least 6 inches for residential driveways. The next sentence in the same guide reads, in full: “In colder climates, continually wet or weak soils will require that bases be thicker.”

Whether that clause's “in colder climates” scopes the whole sentence, including the wet-soil condition, is not settled by ICPI's own wording, so no Naples base rule is drawn from it here; base thickness for a given site is the installer's design question. What ICPI does state plainly is that adequate compaction of the base, like the soil subgrade under it, is critical to minimizing settlement of an interlocking concrete pavement.

The base sits underneath the visible surface, but ICPI ties it directly to a problem that shows up on top: a poorly draining base can turn a sealer cloudy, and a source of efflorescence under the pavers, in the sand, the base or the soil, moving through the joint sand or the pavers, is one of the conditions ICPI lists behind pavers or a sealer whitening.

The base is one source on that list, not the only one. The rest of ICPI's causes, set out under why a sealer turns white or cloudy, include conditions at the time of sealing, such as a surface and joints that were not dry, so a whitened sealer does not by itself point to the base.

ICPI is explicit on this point: joint sand stabilizers do not add to the structural, load-bearing capacity of the pavement. A stabilizer helps hold sand in the joints; it does not carry the load the base was designed to carry.

Edge restraints are the other structural piece ICPI names, providing the lateral resistance that keeps the paving units interlocked, and the bedding sand above the base is a nominal 1 inch uncompacted layer that ICPI says should not be used to compensate for an uneven base. A settled or sunken run of pavers points to the layers beneath the surface and is repair work for an installer, the question taken up on will sealing fix sunken pavers; the same point, that neither a stabilizer nor a sealer stands in for the base, comes up when weighing an installer's no-seal advice. The base is not always aggregate: BIA holds a mortar-set pavement to a concrete base only. The base under any paver surface, a reclaimed Chicago brick patio included, is the installer's call.