I need to use 140mm wide 7N blocks underground below a two storey timber frame building (this is the inner leaf). There will also be an outer leaf below ground formed of concrete blocks on their side to make a 215mm wideleaf (building control requirement as it will be retaining earth abovethe level where the cavity will be backfilled with concrete) . Building control are happy with 3.6N forthis leaf but presumably 7N would also be OK. Could you advise on the relative merits of lignacite versus lignacrete blocks for this use please? The only obvious thing that I can see is lignacite being lighter and hence eassier to handle.

Our Answer:
Recommend 7.3N strength blockwork for outer leaf. Lignacite is lighter, Lignacrete more cost effective however exceeds 20Kg unit weight above 100mm thickness.

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