Does a raft slab need a different sub-base prep than other slabs?

The basic principle is the same — a compacted, well-prepared sub-base — but a raft slab’s sub-base prep is genuinely driven harder by the soil conditions that made a raft the right choice in the first place, since it’s usually specified for reactive or otherwise difficult ground.

Your engineer’s design will typically call for a specific sub-base treatment (a particular compaction standard, a membrane, sometimes an engineered fill layer) tailored to your soil report, rather than a one-size-fits-all approach used across every slab type.

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