I had the same problem when I first started.
I use the bottom of a soda can or in some cases a beer can, LOL. I have an old wooden stick I use to mix with.
I have a 1 minute mixing rule, mix the hell out of it for a minute, the bottom of the can is a prefect mixing boil. Don't worry about the bubbles they'll come out.
Another rule I have is, I never clear no more than two lures at a time (note I fish big crankbaits) because I mix for so long the D2 starts gitting thick about the time I finish brushing on the 2nd lure. Sence I started following my two rules I have never had another lure come out tacky. Maybe this will be some help also.