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[boggis]

hi all, I hope someone can guide me, I want to build a block storage shed on the site of an old patio. This is a raised area contained by a retaining wall, 700mm high, filled with hard core; I have lifted the patio slabs. The storage is not going to be very high- around 1800mm- but it has to be sturdy! Do I have to dig out all the hard core in order to lay concrete foundations or can I build directly onto the existing surface? Thanks