Hard core soling is a fundamental technique used in construction to create a strong and durable subbase under floors, foundations, and pavements. This soling can be carried out using either bricks or rubble stones, depending on the requirements and materials available at the site. The primary purpose of soling is to provide a cushioning layer that evenly distributes loads and prevents direct contact between the soil and structural elements, thus enhancing stability and longevity.
Understanding Rubble Stone Soling
Rubble stone soling involves laying hard stones like black trap, granite, basalt, or other locally available stone varieties under floors or foundations. These stones must be carefully selected for their hardness, durability, and freedom from defects. Proper sizing of the stones is crucial, and specifications often dictate the exact size required for the job.
Preparing the Surface
Before laying rubble stone soling, the surface must be meticulously prepared. This preparation involves clearing away all loose materials that might compromise stability. The surface is then leveled, watered, and compacted to create a firm base. Any trenches needed for cables or pipes should be completed prior to starting the soling process to avoid future disruptions.
Procedure for Laying Rubble Stone Soling
Once the base is ready, the stones are carefully placed. They should be set as closely as possible and firmly packed to prevent movement. Stones are laid with their largest base area resting on the sub-grade to ensure maximum stability. The thickness of the soling layer is usually specified—commonly 230 mm or 150 mm—or as per project requirements, with an allowable tolerance of 25 mm.
After positioning the stones, the gaps between them (called interstices) must be filled with quarry spoils or the largest stone chips available. This filling must be compact and solid; simply spreading loose chips is not acceptable as it undermines the subbase’s integrity.
Finishing Touches and Compaction
Following the filling of the interstices, the entire surface should be examined carefully. Any protruding stones are removed or knocked off with a hammer to avoid unevenness. The spaces between the stones are then filled with approved murrum, a type of fine gravel, to lock the stones in place.
Excess murrum must be removed to maintain a clean surface. The soling is then watered and compacted thoroughly using either mechanical tampers or heavy wooden log-rammers. Proper compaction is essential to create a dense subbase capable of bearing loads without shifting.
Finally, the surface is given the required slope or level to ensure proper drainage and structural alignment. Throughout the process, contractors must exercise caution to avoid damaging any concrete surfaces in contact with the soling.