OK,quick question! I am about to lay a lawn in my rear garden, the previous owners had decked most of it and layed the frame on top of a load of fine gravel. Now that I have removed the decking boards and dug down into the soil it is VERY sandy. Obviously I am going to put down top soil. My question is , should I remove every last bit of gravel or will it be ok to remove say half and let it mix with the sandy soil and top soil I have a snot sure how this will affect drainage. Hope this makes sense