I am looking to lay a raised patio of sandstone on an existing area of lawn. As I want to raise it by 6 inces or so, is it ok to dump hardcore on top of the exiting lawn and whack it down or do I need to dig out first? I'm hoping I can avoid digging out for obsious reasons but it will also mean a lot more material needed.
If you don't remove the topsoil it will gradually shrink down and your patio will become uneven. Also, weeds will grow through it since the topsoil will always contain weed seeds, and nothing stops the plants. If you can't or don't want to remove all of the topsoil you might get away with just taking out the first few inches, back filling with rubble, and then putting down a dry mix concrete on top of it. Much depends on what you intend to go on the patio in terms of weight.