Ernie, I assume you're talking about using a hopper gun to shoot this texture. Your mix will basically need to be slightly thinner than a pancake batter to spray correctly, but there's more to it than the mix ratio. It also depends on what orifice you spray with, and at what pressure.
The smaller the orifice, the finer & more consistent the spray; higher air pressure will also put out a finer spray. You'll probably want to play around with your orifice & pressure settings to get the look you desire.
You may also wish to consider thinning your mud with water instead, then painting the wall/ceiling unless you're planning to shoot fairly heavy. On a lighter, finer-looking shoot, you'll probably not completely cover enough to not have to paint the finished product. Good luck