August and September is the  time to think about how thick my lawn is? I would make sure all the weeds are gone before I think about powerseeding. You dont want to stir up the weed seeds if your lawn is a weed field. Make sure all weeds are in the process of dying before you start to add to your lawn. The steps are very important your trying to build strong turf that you and your family can enjoy.

When power seeding make sure you measure your lawn so you apply enough grass seed. Also run the power seeder North, South, East and  then West to get better results. I always apply lime and a starter fertilzer to get the soil ready to germiante the best lawn in the neighborhood.