Hardcore is the material put under floors. It is used as a sub base after building the foundation wall to make up levels before casting the ground floor concrete slab. The recommended is hard stone ballast or quarry waste that should not pass a sieve of more than six inches when broken down. This shall be free of weeds, roots, vegetable soil, clay, black cotton soil or other unsuitable materials. Broken stones or brick cuttings can also be used as hardcore.
To lay hardcore under floor beds, use well graded smaller pieces mixed with fine materials. This will give a dense compact mass after consolidation. This shall be laid in layers not exceeding ten inches of consolidated thickness. Sufficient fine materials shall be added to each layer to give a gradation necessary to obtain a solid compact mass after rolling. A ten tonne smooth wheeled or two tone vibrating roller should be used to compact each layer.
Compact each layer with eight passes of the roller when laying hardcore under floor beds. Add sufficient water with every pass to obtain maximum compaction. To each layer add a fine layer of sand or quarry dust forced into the hardcore by a rolling vibrator. All the materials used must always be dry to avoid caking or stickiness. This may allow pockets of air or free spaces. This may sink when the hardcore is loaded with weight. If the sand is absorbed into the holes between hardcore then keep compacting.
Thoroughly compact the hardcore filling under floor beds until sand is not absorbed. The top surface should be made level. The levels are done or graded to the required falls. After this is done a blinding layer of similar broken materials is added. This is of at least one inch in thickness. A ten tonne roller is used to smoothen the surface. This mass of hardcore is now ready for anti termite, damp proofing and mesh reinforcement material before concreting the ground floor slab.