Thanks for your reply. This is the old patio. Other than weeds and slightly uneven in some places, it was fine. I am being wary and more want to check that this is something that other people would ordinarily do?
We recently had our old sandstone slabs taken up ready to be replaced with a porcelain patio. We have been told the existing base is solid enough to just tidy it up and relay new slabs over the top. I am not convinced. Images attached. Any advice would be appreciated. Thank you.