Fill Dirt

Fill dirt is subsoil taken from below the topsoil layer. It has very little organic content, and that is the entire point: organic matter decomposes, and anything that decomposes under a slab or behind a wall leaves a void. Voids become settlement, and settlement becomes cracks.

Because it is unscreened, fill dirt arrives with clods and the occasional rock. On a grading or backfill job that does not matter. If you need something clean enough to finish by hand, order topsoil or sandy loam for the final lift instead.

Fill placed in one deep dump will never reach density no matter how long you drive over it. Place it in lifts of six to eight inches, water each lift to roughly the consistency of a wrung-out sponge, then compact with a plate compactor or a jumping jack before the next lift goes down.

A properly compacted clay fill loses very little height over time. An uncompacted one can settle six inches or more in a year, which is how patios end up sloping back toward the house.

For anything structural — a slab, a shed pad, a driveway subgrade — talk to your engineer about a compaction spec before you order. It changes how much material you need, because compacted volume is smaller than loose volume.

Filling a demolished pool takes more material than people expect and demands strict lifts, because the shell area is deep and the surrounding ground is already disturbed. Measure the pool's real volume, add ten to fifteen percent for compaction, and plan for the truck to need clear access to the back yard or for a skid steer to shuttle it.

For pad building, allow for the pad footprint plus a batter on all sides — you cannot stack dirt vertically. A one-to-three slope is a safe default, which means a two foot rise needs six feet of shoulder on each side.