Lime concrete sub-base for slabs

with Saint-Astier® NHL

200 kg of Saint-Astier® NHL 5 or 150 kg HL 5 (Hourdex® or Tradiblanc®) per cubic metre of well graded sharp sand, 6 mm to 0.075 mm.

Mix dry to achieve a uniform colour in a pan mixer or roller pan mill. Slowly add clean water until the correct moisture is achieved (semi dry) – just sufficient to allow mix to bind when squeezed in hand. Free fall mixers can cause balling.

Outdoors > Lay on a compacted sub-base of clean 50 mm screened aggregate (75 mm minimum). Should a membrane be required use a geotextile (not polythene).
Indoors > Lay on a compacted sub-base of clean 75-50 mm aggregate (100 mm minimum). The greater the thickness of the sub-base, the better the insulation properties. Damp proof membranes are not necessary.

Placed in a single layer of 50 mm. It should be well rammed either by hand or with a mechanical compaction plate to the desired level.
Form mechanical key and lay a further 20 mm loose layer ready to set down slabs. Lay slabs as normal.