Ground supported floor construction with concrete

Any ground supported floor should meet the requirement to resist the passage of moisture from the ground if the ground is covered with dense concrete laid on a hardcore bed and a damp proof membrane is provided. Unless it is subjected to water pressure, which is likely in the case of buildings on very permeable strata such as limestone or gravel (in which case see paragraph 5.11), a concrete ground supported floor may be constructed as follows (see Diagram 5.1) – (a) well compacted hardcore bed, not greater than 600 mm deep (if the hardcore bed is deeper than 600 mm, there may be a risk of excessive settlement and cracking of the floor slab; in such cases, a suspended floor slab is advised), of clean, broken brick or similar inert material, free from materials including water soluble sulfates in quantities which could damage the concrete (see BRE Digest 276 Hardcore); (b) concrete at least 100 mm thick (but thicker if the structural design requires) to mix ST2 in BS 8500-1 or, if there is embedded reinforcement, to mix ST4; and