Hardcore/Scalpings?

Building extension and a bit of a steep learning curve. Is this correct?

Hardcore or scalpings well compacted.
Wacker plate to compact
2 inches of sand min and use wacker plate to compress
DPM
Insulation
Concrete.

What size hardcore? Is scalpings the same as hardcore and does it come in sizes? How do I work out how much to buy?

Where is best place to buy?

Sorry for all the questions and hope you can help me.

That's ok. I'd add a 1000g vapour membrane between the concrete and the insulation but not everybody insists in this. The hardcore is 'type 1'. Full title is MOT type 1 (Ministry of Transport). Or some just call it MOT. Basically it is crushed stone from 40mm down to dust so it compacts well. It should be compacted in layers no more than 150mm thick/deep at a time and to a maximum overall of 600mm. Any deeper than that you either need an engineered fill or a suspended floor. Order it by volume.

thank you so much John of your input. Much appreciated.

Thanks for the MOT definition...I've been searching for a while now for what the definition meant and even asked on here and nobody could answer. Should have been obvious

I've got an excess of a few tonnes of Type 1 MOT from my front garden (over ordered). What else can the Type 1 be used for other than for under block paving? I'm trying to avoid giving it away or throwing it and have lots of other project work to do including extensions etc, but didnt think you could use this for that.