We use a commercial-grade, non-yellowing, UV-resistant, high-solid acrylic-based sealer. It is designed to last three to five years, depending on a variety of factors such as exposure to sun-light, traffic, and the surface to begin with. We have found that the frequency at which concrete should be re-sealed largely comes down to personal taste: some of our clientele prefer a clean, bright, glossy surface (seal every year), whereas others like to seal once and then let the concrete develop its own patina over time. The good news is that the sealers we use do not abruptly fail or peel away. It is a slow process of incremental degradation that is largely indiscernible. Most any surface can be cleaned and sealed, or resealed as the case may be.