Typical applications for polyurethane sealers include:
Floors in high-traffic areas, to provide good resistance to scuffs and staining
To enhance the beauty of colored, stamped or exposed-aggregate concrete
Most polyurethanes are moisture intolerant until they cure, so they should not be applied to surfaces if any water is present. A chemical reaction will occur that results in foaming and bubbling. They also don't allow for moisture vapor to move out of the concrete, which could present problems on some exterior concrete surfaces, such as driveways.
How to apply
Polyurethane sealers require more care when applying compared with single-component sealers, such as acrylics. Avoid applying water-based polyurethanes with a garden-type pump-up sprayer, since they don't reach the level of pressure needed to achieve a thin, even spray pattern. Instead, use a low-volume, high-pressure airless sprayer. Polyurethanes can also be applied with a micro-fiber mop, using a push-and-pull motion to get thin, even coverage.