I have acquired a number of (plastic) concrete slab moulds (riven face) with the intention of casting my own slabs.
I plan to trial different aggregate types (coarse gravel / quarry dust), and adding colourant to see what comes out best, using a basic 1:2:3 mix.
I'm aware I will need to use a release agent of some sort in the moulds. I know vegetable oil has been suggested here before (rather than the significantly more expensive release agents you can buy). Anything else anyone would advise using?