Improving the life of a coating such as polyurethane, acrylic or epoxy can be achieved with the addition of a small amount of a abrasive such as Aluminum Oxide, White Aluminum Oxide or Silicon Carbide. These materials are significantly harder than the coating material and will increase the scratch resistance of the coating with minimal impact on the other properties of whatever coating you are using.
The specific type of abrasive will depend on a variety of job specific requirements including color, clarity and thickness. The size of the abrasive used is generally a very fine grade such as a 600 or 800 mesh but larger grit (~240 mesh) can be used in thicker coating. The addition rate is also very dependent on the coating you are using specifically related the solids content. Rates of 3 – 5% (about 1/2 pound per gallon) are common.