(Figure A) Over time a normal lawn will compact itself. A compact ground not only tends to cause thatch build up but also greatly reduces the amount of air and nutrients that enter the ground. With less nutrients to feed on and a harder ground to break into, grass roots can't grow and often the grass itself turns into an ugly brownish-yellow color ultimately provoking thinning of the grass.

 (Figure B) Compaction is not only provoked from walking and mowing on your lawn, but also by rain and irrigation. Compaction occurs primarily in the 1" to 1-1/2" of the soil surface. Aeration can prevent or solve compaction and thatch build up. By using a core aerator, small plugs of soil are pulled from the ground allowing a better passage of air, water and nutrients.