Base Course Gravel: Material Guide

Road Base is our first choice for base course. It is a gray crushed stone graded 3/4 inch minus, which means the largest pieces are about 3/4 inch and everything smaller down to fine dust stays in the mix. Those fines are what let it pack into a dense, hard layer under a compactor.^[1]

Driveway Gravel belongs in the layer above a base. Its clean, washed pieces give a gravel drive a surface that drains and grips. Spread over compacted Road Base, it makes the classic two-layer drive: a hard pack below and a loose, free-draining top.^[1]

Stone Dust Screenings are the finest member of the family. They go on top of a base as a thin setting bed under pavers or flagstone, or as a smooth surface for a garden path. They level well, but they lack the coarse stone to carry heavy loads on their own.^[1]

For soft, wet ground or a deep build, some builders start with a layer of larger crushed stone at the bottom and finish with Road Base on top. The larger stone bridges soft spots, and the finer base above it compacts into a smooth working surface.^[1]

A good base needs a range of particle sizes. The 3/4 inch pieces carry the load, smaller chips fill the spaces between them, and the fines fill the spaces between the chips. When the blend is right, compaction squeezes out the air and leaves a dense layer with almost no room to move.^[1]

Angular particles matter too. Crushed stone has fractured faces that lock together under a compactor. Round gravel in the same sizes compacts poorly because the stones roll past each other. A base made of crushed stone stays put under traffic and through freeze and thaw.^[1]

Moisture control is the third need. A base should be dense enough to carry weight without holding so much clay that it turns to mush when wet. Road Base is made from crushed rock, so its fines are mostly rock dust, and it keeps its strength when damp.^[1]

Weight is a quick sign of density. A cubic yard of Road Base weighs about 2,800 lb, heavier than clean stone of a similar size, because the fines take up space that would otherwise be air.^[1]

Mark the area and dig it out deep enough for the full base plus the surface layer. Remove sod, roots and dark topsoil until you reach firm subsoil. Shape the bottom with the same slope you want on the finished surface, so water drains the right way from the start.^[1]

Compact the subsoil with a plate compactor. On clay or wet ground, roll out a woven geotextile fabric next. The fabric stops the base from pushing down into the soil and keeps mud from rising into the stone.^[1]

Spread the Road Base in lifts no thicker than a few inches. Dampen each lift with a hose so the fines can slide between the larger pieces, then make several passes with the compactor. A lift that is too thick stays loose at the bottom no matter how hard you pack the top.^[1]

Check the surface with a long straightedge or a string line as you build. Fill low spots and compact again. When the final lift is firm and even, with a uniform gray surface and no loose pockets, the base is ready for pavers, a gravel top, a shed or a slab form.^[1]

Depth depends on the job. A walkway or a small patio over firm soil can use a thinner base. A patio with heavy furniture, a shed pad or a driveway for cars needs more, and soft or clay soil calls for more still.^[1]

At 4 inches compacted depth, 100 square feet takes about 1.73 tons of Road Base. At 6 inches, the same area takes about 2.59 tons. Those two depths cover most patios, shed pads and home driveways.^[1]

Thinner layers have a place. At 2 inches, 100 square feet takes about 0.86 tons, which suits a leveling course over an existing base. At 3 inches it takes about 1.30 tons, a sensible depth for a garden path over firm ground.^[1]

To get the total, multiply length by width for the area, divide by 100, and multiply by the tonnage for your depth. Road Base loses volume as it is compacted, so order a little more than the math shows, and keep a spare pile for patching.^[1]

Road Base is sold by the ton and delivered by dump truck. The delivered total depends on how many tons you order, how far the stone travels from the supplying yard to your site, and what size truck can reach the drop spot.^[1]

Larger orders spread the trip over more tons, so the amount per ton tends to drop as the order grows. A small patio order still needs a whole truck trip, which is why combining jobs, such as a shed pad and a path, into one delivery helps.^[1]

Base stone is one of the less expensive materials per ton, because crushed rock is produced near most markets. The bigger factor in your total is the depth you choose. Skimping on depth saves a little at the start and can mean rebuilding later.^[1]

Enter your ZIP in the box on the site to see the delivered figure for your area, then use the area calculator to turn your measurements into tons.^[1]

Using clean stone as a base is the first mistake. Washed gravel drains well but never packs tight, so pavers rock and drives rut. Keep clean stone for drainage and surfaces, and use a base with fines for the structural layer.^[1]

Skipping the compactor is the second. Spreading Road Base and walking on it does not pack it. Rent a plate compactor and pack each lift until a boot heel leaves no mark.^[1]

Building on topsoil causes slow sinking. Organic soil keeps settling as it decays. Dig down to firm subsoil before the first lift goes in, even if it means a deeper hole.^[1]

Ignoring water undoes good work. A base with no slope and no outlet holds water, softens and heaves in freezing weather. Slope the surface away from buildings and give runoff somewhere to go.^[1]

Rushing the finish is the last one. Pavers, a shed or a gravel top laid on a base that was never checked for level will show every dip. Take the time to run a string line, fix low spots and compact one final time before the surface goes on.^[1]