Topdressing of turf could mean one of two techniques.
One meaning is compost-topdressing with a very thin layer of compost to provide nutrients. To learn about compost-topdressing, follow this link offsite to our Soil3 product page: Topdressing with Soil3.
The other meaning of topdressing is to level sod, that's why we're calling it leveling-topdressing. This is when a thick layer (no more than 1/2 of the blade height) of sand or topsoil is spread over turf with the intention of improving the surface texture of the land under the turf - to even out bumps and depressions. The goal of topdressing like this is to create a smooth playing surface, commonly done on sports field and golf courses, and is often necessary to smooth newly established home and commercials lawns. Topdressing for evening out turf requires a thicker layer of topdressing material (compared with compost-topdressing as a fertilizer application).
So that you can level your lawn and provide nutrition at the same time, we developed a mixture that's 70% sand and 30% Soil3 organic compost. It's called Level Mix and sold in a 1 cubic yard BigYellowBag. Instructions on how to use Level Mix and where to purchase it can be found on our sister website, Soil3.com: How to Level Your Yard with Soil3's Level Mix.