Sammy,
May I make a suggestion. When next at the Hobby Store (or $Dollar Shop) get a variety of soft brushes. Brushing allows you to blend the fillers evenly over the bases. It's so easy, you will only need a few practice runs.
Hardware shops (Builder's Yards) and Plant Nurserys sell a variety of sands, gravels, stones, fillers at reasonable prices.
Happy Collecting
Oberstinhaber