How to compact a platform properly
Proper compaction is done in thin layers, compacted separately, not in a single thick layer. The compactor roller is used on open surfaces, the vibratory roller on soil fills, and the plate compactor in narrow areas and next to kerbs, where the large machine cannot reach.
Compaction is the least spectacular stage and the one that decides whether the work lasts or sinks. A badly compacted platform looks perfect at handover and breaks up in the first winter.
The layer rule
The material is laid in layers and each layer is compacted separately, before it is covered by the next.
The reason is simple: the compaction effect decreases with depth. If you lay a thick layer and go over it with the roller, the top gets denser, while loose material stays underneath. It only shows a few months later, when bumps and cracks appear.
The layer thickness depends on the material and on the machine used. The heavier the machine, the thicker the layer it can compact — but the rule stays the same: several thin layers always beat one thick layer.
Which machine, for what
Tandem compactor roller — two smooth drums, for open surfaces and for asphalt. It gives a smooth, uniform surface.
Single-drum vibratory roller — a vibrating drum, for soil and ballast fills. The vibration transmits energy deep down, so it compacts thicker layers than a smooth roller.
Plate compactor — for narrow areas, next to fences, kerbs, manholes and foundations, where the large machine cannot get in. It is also used for block paving.
Trench rammer (jumping jack) — for narrow trenches, where not even the plate compactor fits.
Two or three of them are usually used on the same job. The area the roller does not reach is exactly where settlement appears, if it is not compacted with the plate compactor.
Moisture matters more than you think
Soil compacts best at a certain moisture content. Too dry, and the grains do not slide past each other and do not pack together. Too wet, and the water keeps the particles apart.
In practice: if the material is dry and dusty, it is watered. If it is mud, you wait. Compacting material that is too wet is wasted time.
How many passes
There is no fixed number. You compact until there is no more visible settlement under the machine — that is, until the drum no longer leaves a mark. With some materials, too many passes can even damage the structure of the layer.
On jobs where a warranty is required, the degree of compaction is checked with laboratory tests.
The mistakes you pay for
- The topsoil is not stripped. The organic matter rots and leaves voids.
- A single thick layer. It is compacted only at the surface.
- Narrow areas are skipped. Edges and areas next to manholes sink first.
- Material that is too wet is compacted. Nothing is achieved.
- Water drainage is not provided for. Water collecting under the platform undoes everything you compacted.
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