Substructure and ground-bearing floors

Also see:

5.1.10Harmful or toxic materials

Harmful or toxic materials present in the fill or in the ground shall be identified to the satisfaction of NHBC and not affect the performance of the substructure and ground-bearing slab.

Precautions should be taken by either:

  • ensuring that made ground and fill materials are free from harmful or toxic substances, or
  • designing the construction to contain, resist and prevent the adverse effects of such materials, using means acceptable to NHBC.

Tests for sulfate content should comply with the recommendations of BRE Special Digest 1 Third Edition by a suitably qualified person who has a detailed knowledge of the:

  • material being tested
  • proposed conditions of use.

The samples tested must be representative of the material, so it may be necessary to collect multiple samples to identify characteristics.

Where there are likely to be harmful levels of sulfate:

  • the floor slab should be of an appropriate mix to resist sulfate attack or be protected by an impervious layer of 1200 gauge (0.3mm) polyethylene sheet, or 1000 gauge (0.25mm) where it complies with Technical Requirement R3. This may also serve as a DPM
  • the concrete blocks in substructure walls should be sulfate resistant and suitable for the fill and ground conditions
  • the mortar should be sulfate resisting to comply with of BS EN 1996-1-1.

Fill containing expansive materials or chemicals is not acceptable for use as infill or backfill.