we got some of ours from when they took them out from the pavement to replace with tarmac. they're extremely heavy and they need to be for cars, my dads put them down on mud, but when it gets wet it splashes up when weight is put on them, already dug them up to but gravel underneath but ran out so need to do it again.
also isn't there new regulations for drives/patios now too, to make you allow adequate drainage?
also isn't there new regulations for drives/patios now too, to make you allow adequate drainage?