Laying Hardcore Under Concrete Floor Beds

Hardcore is the material put under floor . 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 kind of hardcore is hard stone ballast or quarry waste that should not pass a sieve of more than six inches when broken down. Care should be taken to ensure that the hardcore is 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. It is laid in layers not exceeding two hundred and fifty millimeters 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 ton smooth wheeled or two ton 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 as this may allow pockets of air or free spaces which may result in sinking when the hardcore is loaded with weight. If the sand or quarry dust is absorbed into the holes between hardcore then keep compacting.

Thoroughly compact the hardcore filling under floor beds until sand or quarry dust 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 at least twenty five millimeters in thickness is added. A ten ton roller is used to level the surface. After the mass of hardcore has been compacted and rolled to the right level anti-termite is applied to the surface. Damp proof membrane and mesh reinforcement material are then laid on the surface in readiness for concreting of the slab.

Fundi Mjanja.