Lawn thatch occurs on every lawn, and it's not typically a problem. What it amounts to a layer of organic debris. Normally microorganisms help to decompose thatch and keep it at a manageable level. However, when thatch builds up on your lawn, it can keep water from penetrating to the soil. This can cause grass roots to grow upward into the thatch instead of down into the soil. Although you can rent machines that will help cut away the thatch in layers, a gentler solution is a liquid grass dethatcher that feeds the microorganisms.
Mix 1 can of beer with ¼ cup sugar, water, ammonia and dishwashing liquid. Make sure that your liquid is not the type with antibacterial agents in it. You want to encourage the microorganisms to grow, not kill them.
Pour the solution into a hose-end sprayer.
Apply the solution to your lawn with the sprayer.
You can substitute a carton of plain yoghurt with active cultures in it for the beer. Both beer and yoghurt contain lactobacillus bacteria and enzymes that help to break down thatch. These enzymes feed on sugar. The sugar in the solution helps encourage the lactobacillus bacteria to grow and to decompose the organic material found in thatch at a faster rate. When the sugar is used up, the bacteria die back.