Stage by stage house building It is advisable to use solid blocks in foundations if you don’t plan on putting concrete in the hollow part of the foundation blocks. All concrete are advised to be vibrated to reduce voids by use of a poker vibrator. Hollow blocks are ideal for interior walls as they help with acoustic control/soundproofing.
States in building a house. All hardcore in foundation should be sand blinded or soil filled to reduce gaps that may use up more concrete and also create large voids that could later cause the floor to crack from settlement if concrete is not well distributed between those hardcore gaps. Damp proof membrane (nylon) is then laid upon the sand blinding or soiling and over the foundation blocks before the grade slab is poured to prevent rapid loss of water from concrete, groundwater absorption during the rains by the slab and walls, which will create dampness in buildings, leading to the walls always being moist hence leading to paints flaking or peeling off. Neat construction by the way.
Credit: Clueless Junkie