What is the best way to prepare a lawn that has fair grass already to receive new sod? Till up old grass and smooth off? Spray with Roundup and lay new sod immediately? No prep...lay sod on top of original grass? I intended to find out. However my wife would not allow me to kill parts of our front yard for the test. Shady back yard will have to do. I only bought one roll of sod (2 ft by 5 ft.) June 14, 2012. The area is irrigated--about 20 minutes daily. I tilled up the center area 2 ft by 2 ft--by spadeing up with a shovel. I left the grass untouched on the right end 18 inches. I treated the left end (18 inches) with Razorburn (Glyphosate plus diquat). I used snow shovels to make a nice clean edge with no overspray. Does anybody care to predict the results?