sm_jamieson wrote:

Just putting in the hardcore (MOT 1) for my floor slab. 100mm required
(BCO agreed).
First floor slab I've done.
To what depth should I rake it out before compaction to end up with
100mm ?
In other words, how much should I expect it to compact ?


That depends how you are compacting it, and what with.

I assume that you are using crushed limestone with a relative density
of around 2.7 t/m3. Loose, it is about 1.3 t/m3. Compacted
systematically with mechanical plant at the material's optimum
moisture content, and it can go as high as 2.1 t/m3. Depending on how
you compact it, and how meticulous you are, it could be anywhere
between 1.6 and 2.0 t/m3 (tonnes per cubic metre).

If you wanted me to take a stab at a rough nominal thickness to start
with, I would suggest 140mm for a final thickness of 100mm. But that
is just a very rough guess. All depends on the method of compaction.