Hardscaping glossary

Subgrade - the native soil left after excavation, before any aggregate goes in. Everything sits on it, so if it's soft or wet, the contractor needs to say so before continuing.

Aggregate base - the compacted crushed stone layer between subgrade and bedding. It carries the load and drains. Its thickness and material should be named in your contract.

Lift - one layer of aggregate placed and compacted before the next goes on. Today's Homeowner describes tamping around 2 to 3 inches at a time. "Compacted in lifts" in a contract means the base was built in layers, not dumped.

Bedding layer - the thin, screeded layer directly under the pavers that lets them be set to a true surface. It is not the base and cannot substitute for one.

Edge restraint - the perimeter barrier that stops outer units migrating outward. Cheap, essential, and often skipped.

Joint sand / polymeric sand - the material filling the gaps between pavers. Polymeric sand contains a polymer binder activated by water; Today's Homeowner reports it costs roughly three times mason sand and typically stays effective around five years.

SRW (segmental retaining wall) - a wall built from modular concrete units rather than poured concrete. CMHA runs an installer certification specifically for these.

ICP / PICP - interlocking concrete pavement and permeable interlocking concrete pavement. CMHA certifies installers in both. PICP is the system EPA-style permeable paving uses, with an open-graded reservoir base.

Geogrid - a synthetic mesh laid in horizontal layers into the soil behind a taller retaining wall to reinforce the soil mass. If your wall design includes it, that is normally a sign the wall is engineered rather than a simple gravity wall.

Drainage zone - the gravel column behind a retaining wall that lets water escape instead of loading the structure. Today's Homeowner describes 4 to 6 inches of gravel behind each course.

Surcharge - a load above and behind a retaining wall: a driveway, pool, slope or structure. It changes the engineering and often the permit requirement.

Daylight - used of a drain pipe, meaning it exits at the surface somewhere downhill so water actually leaves. A drain that doesn't daylight isn't finished.