A compactor is a machine that drives air out of soil or stone so the ground stops settling under whatever you build on it. Three families do that job: vibrating plates, rammers and rollers. Plates hire near $60 to $90 a day and rammers near $70 to $110, and the material you are compacting picks between them.
Compaction is about removing air, not flattening
Loose fill is grains with gaps between them, and those gaps close under traffic and rain long after the job is finished. A compactor uses vibration or impact to settle the grains into a dense arrangement now, so a patio, slab or paving base holds its level rather than dipping over the first winter.
Granular material wants a plate, cohesive wants a rammer
A vibrating plate shakes stone, sand and crushed base into place across an open area and is the right tool for paving and patio bases. A jumping jack rammer hits a small footprint hard, which is what silt and clay need, and its narrow shoe fits inside a trench where a plate cannot work.
Thin lifts beat a bigger machine
No compactor reaches all the way down through a deep pile of loose material. Spread in layers of a few inches, compact each one, then spread the next. A weekend of work over deep fill with a big plate produces a firm crust on soft ground, which is the failure that shows up as a sunken corner later.
Reversible plates and when they pay
A single direction plate walks forward and must be turned by hand at the end of each pass. A reversible plate drives both ways, weighs more and compacts deeper, and on any area beyond a small patio it saves enough labour to cover the extra on the rate. Ask which one the quoted price is for.
Questions people ask about what is a compactor
How many passes does a plate compactor need?
Three to four passes over each layer is a common working rule, with the layer kept to a few inches. Stop when the plate stops sinking into the surface and starts riding on top of it. Slightly damp material compacts far better than bone dry stone.
Can I use a compactor on wet clay?
A rammer will work cohesive soil, but saturated clay simply moves rather than compacting and will pump water to the surface. If the material squelches under the machine, the honest answer is to wait for it to dry or to dig it out and replace it with stone.
Do I need one for a small paving job?
For anything more than a couple of slabs, yes. Hand tamping a base by foot or with a post is slow and uneven, and a day on a plate costs less than lifting and relaying paving that has settled unevenly a year later.