Sandunderlag

Sandunderlag is a layer of sand used as a base or bedding beneath other surfaces, such as paving stones, bricks, terraces or outdoor floors. The layer is chosen for its granular makeup, which allows for leveling, drainage and a workable bed for laying material on top. In practice, sandunderlag helps to fill small irregularities in the subsoil and to distribute loads more evenly.

Materials commonly used for sandunderlag are clean, angular sharp sand or building sand. The thickness is not fixed and depends on the surface being installed and the expected loads; it is typically a few centimeters thick, often around 2–5 cm for small outdoor surfaces and thicker for heavier paving applications. Sometimes a geotextile membrane is laid between the soil and the sand to improve drainage and prevent mixing of layers.

Installation generally involves preparing the ground by removing vegetation and losse material, optionally laying a geotextile fabric, compacting the subgrade, and then spreading and leveling the sand. The surface is finished by placing the final material (pavers, tiles, or boards) on the sand and compacting it. After installation, joints between paving stones are filled with jointing sand to prevent weed growth and to improve stability.

Maintenance mainly consists of checking the surface for unevenness caused by settling and replenishing sand in joints as needed. Sandunderlag can degrade in poorly drained or frost-prone soils, and in such cases a stronger base (such as a crushed-stone sub-base) or alternative bedding methods may be required to ensure long-term stability.