Airbrushing Rubber Treads

Last ngiht I tried to airbrush with acrylics for the first time.  I was trying to coat two rubber tank treads with some black acrylic paint.  But the paint beaded up on the treads, like water on a freashly waxed car.  I know adding soap will mitigate this effect, but I am afraid it will also cause my paint to foam as it goes through the airbrush.  Is there some other way to airbrush rubber treads with acrylics?  I was thinking adding bleach?? Or is it better to coat them with Future and then with whatever paint you want?