This is how i made my own square flat paving slabs using some cheap but good quality moulds/molds. i got to the stage now every slab i make is 99100% perfectly formed from the moulds. little to no bubbles on the top surfaces of the slabs! using simple tools producing quality as good as commercial slabs.

Here are some links to the molds i use
34x34x5cm flat paving slabs (produces 30x30x5cm slabs) https://www.amazon.co.uk/gp/product/B...

slab with grove lines 27x27x4cm https://www.amazon.co.uk/gp/product/B...

square patern 29x29cm https://www.amazon.co.uk/gp/product/B...

Any questions Feel free to ask in the comments i will be happy to answer