To kill grass with rock salt, pour enough salt on the area to cover the grass, and walk over the salt to pound it into the ground. Use a vehicle such as a bicycle or riding lawn mower to embed the salt if the area is too large to reasonably walk over with your feet.
As the grass dies, it loses its vibrant green color. It appears brown, stops growing and feels dry to the touch. Some grass varieties are better able to tolerate high levels of salt, so it may take longer for the grass to die.
According to Colorado State University, Fults alkaligrass is among the most salt-tolerant grasses. Bermudagrass is the next most salt-tolerant, followed by crested wheatgrass and red fescue. Kentucky bluegrass, buffalograss and blue grama are among the least salt-tolerant grasses. If you don't know the variety of the grass you want to remove, contact a lawn care specialist for help.
You can undo the damage if you decide you want to grow grass in the area again or if you accidentally get salt on grass you want to keep. According to North Dakota State University's horticulture department, flooding the ground with water three consecutive times will remove excess salt and allow grass to regrow.