If you want thicker turf, might we recommend clover. There are a number of ways that clover can give you a thicker lawn. First, clover deposits nitrogen into your soil, which means that the turf around it will have a safe, steady flow of nutrients all growing season. Second, clover fills in gaps in your lawn, making your yard look "fully green." Clover blends nicely with most turfgrass, which means that, unless you're looking at your lawn up-close, it all will just look healthy and green, all summer long. Third, clover does well in sunny and shady areas, and typically needs less water, which means that no matter what the weather, your clover is keeping your yard green and thick. Finally, clover strengthens weak soil. Its roots serve as natural aerators, it fixes nitrogen, and when you mulch mow, it adds a great amount of organic matter to the soil.

Additional reading:
There's One Lawn "Weed" You Might Want to Embrace
Clover Comeback
Benefits of Planting a Clover Lawn