How to choose the right compactor for your soil type

Granular or cohesive soil?

Granular soils (sand, gravel, crushed base) compact through vibration: it settles the grains and drives out the air. Cohesive soils (clay, silt) compact through impact: they need to be struck and kneaded, because vibration alone leaves them as they were. Mixing them up is the most common and most expensive mistake.

The fist test settles it in a minute. Wet a handful of soil and squeeze it. If it forms a sticky ball that keeps the shape of your fingers, it's cohesive. If it crumbles when you open your hand, it's granular. If your fill is a mix, go with the part that makes up most of the volume.

• Granular → plate compactor or smooth-drum roller.
• Cohesive → rammer or padfoot roller.

If your soil looks like this, use this compactor

The second question is space. A narrow trench, or the strip next to walls and pipes, won't take a wide plate or a ride-on roller. In a yard, a street or a parking lot, a rammer moves too slowly. This table puts both questions together with the SIMAQ machines.

Open area or narrow trench?

In open areas, a plate compactor moves fast and leaves an even surface. The SQ15 PRO has a 12 L water tank for wetting and asphalt work, plus built-in wheels to move it around the site. Once the area grows from a yard to a whole street, a roller makes more sense: it covers more width per pass and doesn't wear out the crew.

In a trench, the rammer fits where a plate can't and compacts deep through impact, without hitting the pipe if you handle it carefully. When the trench is deep or the walls aren't reliable, a remote-control roller keeps people from working inside it.

Lifts, passes and moisture

Compact in 20 to 30 cm lifts. A thicker layer won't densify at the bottom no matter how many passes you make: it looks firm on top, stays loose underneath, and it shows when the floor sinks months later. Make 3 to 4 passes per lift, overlapping each strip.

Moisture matters as much as the machine. Soil that's too dry won't settle and just kicks up dust. Soil with too much water moves like jelly under the compactor and never firms up. If it's dry, water it evenly and wait for it to soak in. If it's soaked, let it dry out or swap the material.

• 20–30 cm lift → 3–4 passes → check → next lift.
• The machine stops sinking and barely leaves a mark → that lift is done.
• The rammer starts bouncing instead of sinking → the soil is dense.

How to tell the job is done right

On site, the most reliable sign is that the compactor stops sinking and the surface no longer changes from one pass to the next. If the contract specifies a compaction percentage, a lab runs the test: compact with that test in mind, not with how the surface looks.

If you're torn between two machines, think about what you'll do most often. A crew that digs trenches almost every day needs a rammer. One that does yards, sidewalks and pavers lives with the plate. And if you do everything, the usual answer is to have both.