I started demolishing an old brick walkway in my backyard and I found sand underneath about a good 3 inches worth of sand. My question is: If I leave the sand underneath and add about 2 inches of topsoil over the sand, will my grass grow on this top soil sitting on top of sand? Is it a bad idea to leave the sand down there? Should I remove it?
I'd recommend removal - a little bit mixed in with soil is fine, but 2 inches of topsoil over 3 inches of sand means, although your grass will grow okay, if its a high traffic area, it won't be 'stable', meaning it'll slip and slide about a bit, so won't remain level and even. If, though, it's not a high traffic area and the only walking across it will be you with a mower occasionally, it'll probably be okay. As its an old path, the risk of salts in the sand will be minimal.