Micro balloons do not work with PVA or aliphatic resins (white and yellow glues). Both 5 and 30 minute epoxies work just fine wilh micro balloons. Just mix up what you need to the consistency of cake icing. If you need it to retain its form add more balloons. You'll get used to it pretty quick and know what you need for a given application. Both epoxies will form a nice smooth finish if you stop working them early enough. You can also smooth them out before the epoxy sets by wetting your finger with denatured alcohol. Regular isopropyl (rubbing) alcohol also works if that's all you have just not as good. Additionally, the more 'balloons' that you add the easier it is to sand. Wet sanding also helps as long as you don't get carried away and soak the surrounding wood with water. Micro balloons are preferred over other fillers due to weight. This is why they are also used on full scale composites. Other fillers (sawdust, baking soda, etc) just add extra weight. You also need to remember that micro balloons are a filler only and do not add structural strength. For that you would need to add chopped fibers.