Paver base depth: how much gravel and sand under pavers

Base depth for walkways, patios and driveways

The base carries the load; the pavers and sand only spread it. The Concrete Masonry & Hardscapes Association (CMHA, formerly the Interlocking Concrete Pavement Institute) sets the minimum compacted base at 4 in for walkways, patios and other foot traffic and 6 in for residential driveways. Those minimums assume ideal conditions: a strong subgrade, good drainage and no freezing. For each one the site lacks, CMHA says to add 50% of the minimum.

A driveway on weak, wet, frost-prone clay works out to 15 in of base. CMHA calls that a rough estimate and sends streets and heavy-duty pavements to a civil engineer; on a site that poor, a local engineer's opinion is worth getting for a driveway too. Where the paver maker's installation guide asks for more than this table, follow the paver maker.

Bedding sand: one inch, screeded, not compacted

The sand is a setting bed, not part of the structure. CMHA's construction tech note calls for an uncompacted, nominal 1 in layer of coarse, washed sand meeting ASTM C33 (concrete sand), screeded flat over the finished base. Do not use it to fix low spots in the base; a thick patch of sand settles more than the sand around it and shows as a dip. Masonry sand, limestone screenings and stone dust are on CMHA's do-not-use list for bedding.

The base below should already have the final slope. The sand is laid at an even thickness, so the pavers follow whatever the base does.

Tons of base and sand per 100 square feet

Each row is 100 ft² (a 10 × 10 ft area) at one of the base depths above. The base is ordered 20% over its finished volume because loose crushed stone packs down under the compactor. Crushed stone is figured at 2,800 lb per cubic yard, as the paver calculator does; crusher run with fines is heavier, at 2,900 lb.

Scale by your area. A 12 × 16 ft patio is 192 ft²: on 4 in of base it takes 3.98 tons of crushed stone and 0.80 tons of sand. On frost-prone clay, two conditions short, the base goes to 8 in and the stone to 7.96 tons. Run the base a little past the paver edge so the edge restraint sits on compacted stone, and add that strip to the base order.

Compacting the base in lifts

A plate compactor can only pack so much stone at once, so the base goes down in layers called lifts, each compacted before the next is spread. CMHA's tech note specifies lifts of 4 to 6 in with a 7,000 lbf reversible plate compactor, compacted to at least 98% of standard Proctor density, and CMHA calls any plate under 5,000 lbf too small. With a lighter rental plate, spread thinner lifts; 2 to 3 in is common practice.

• Compact the soil at the bottom of the dig before any stone goes in. Soft spots get dug out and filled with base.
• Keep the base slightly damp while you compact it; bone-dry stone with fines is hard to pack.
• Make several passes in overlapping, crossing directions on each lift, and check depth with a string line after compaction, not before.
• A 6 in driveway base is 1 or 2 lifts depending on the plate; a 15 in base is 3 to 5.

Geotextile on clay and wet soils

On clay, moist silty soil or ground that stays saturated part of the year, CMHA allows a geotextile between the soil and the base. It keeps the fine soil from pumping up into the stone, which would weaken the base over time. Lay it flat with no wrinkles across the whole bottom of the dig and turn it up the sides. On those soils the extra base depth from the first table still applies; the fabric is a separator, not a substitute for depth.