To get the different colored dots or speckles we use an undercoat gun with only twenty-five pounds of pressure. Higher pressure will give you smaller dots or speckles. Undercoat guns are very inexpensive and available at any auto parts store. They come in a variety of shapes and sizes, some with special pots. We buy the cheapest ones with just a pipe, trigger and handle. They are easy to use and easy to clean.
Once the spraying of the dots is finished you have to wait for the paint to dry before taking off the masking.
Then we brush on the grout color between the rocks... and as quick as that you are done.