Our broader line of coatings products are generally what we recommend for specialized purposes as the cure time when properly mixed is 15 minutes for general set and more than 1 hour for 80% full cure. This leaves ample time for any top application to embed in the coating and is the process used for many applications from specialized floor and roof coatings to rock walls. Alternatively, most aggregates can be combined in moderate proportions to the product before spraying if they do not impair the spray equipment. Our polyurea cartridge kits set in seconds and do not provide enough time to broadcast a medium which will actually settle into the coating. For this reason, applications not specifically requiring pure polyurea are recommended to consider them, and many are offered in our DIY store: https://store.sprayliningandcoatings.com.
If mixing into the product while still in a liquid state, remember that most of the medium additive will settle to the bottom and not provide any surface texture. Also, any sand or other additive will have a much thinner coating of our product which may eventually wear off enough to show the medium used for texture. Your best appearance would include consideration of the color of your medium to ensure it will not be an abstraction if it should be exposed.