Most people mix their groundbait with either white or brown crumb groundbait too, to bulk it out so it lasts longer.
Personally, I do a 50/50 mix of crumb and groundbait. Add a little water at a time and mix it in thoroughly, making sure you get rid of as many lumps as you can. Once you've added enough water to make the mix wet enough to hold together when you make a ball, let it stand for about 10 to 15 minutes. It will absorb the water you've added properly then.
After this time, check the consistency and add a bit more water if you need to. Also, if you're targetting small fish, it's good idea to riddle the mix as well to get rid of the larger lumps as these will fill up the fish quickly.
Throw a small ball into the margin and see if it has the desired effect i.e. explodes and forms a cloud, or sinks and breaks up slowly.
When I'm float fishing, I never use a lump much larger than a golf ball and will feed this every time I loose feed.
Hope this helps.