new shop floor question

yep. :.)

I poured a concrete slab for my shed with a 3inch square lip, I then put a 3in layer of "crush and run" down (this is mixed ungraded stone from a quarry from from about 2in diameter to dust).

Compress it down with a tamper (I used a garden roller).

It's now set like stone, but without the worries of it spalling.

I imagine a mixture of soil, sand, ash, clinkers and gravel would work as well - assuming you are under cover, otherwise, whats wrong with grass?

Forge and woodworking (and auto-fuels/lubricants, too) without walls sounds like a recipe for a shop fire - not a happy thought.