In article , Lobster
wrote:
Am I supposed to sort of jump up and down on the
hardcore a bit before I blind it with sand?!

As the others have pointed out you need to do a bit more than
jumping on it. You should have nothing bigger than a half brick -
if you have, breaking it up in situ with a sledge hammer will
achieve this and compact it at the same time.

If you're putting a polythene dpm over the blinding it will need
to be free of any roughness. If not putting some light polythene
will stop the grout in the concrete draining through and make
levelling it a lot easier.

--
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk
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