Unlike enamels, the solvents in acrylics do not dissolve mold release agents, skin oils, or other contaminants on the plastic surface.
Clean the plastic before painting with a surfactant cleaner, Simple Green solution (both require rinsing) or Windex.
Be sure to use only 90%+ isopropyl to thin Tamiya paints. There have been quite a few posts explaining how to brush paint with Tamiya acrylics, both by me and others on this forum. Try to find them so I won't have to repeat myself yet AGAIN.![Sad [:(]](/emoticons/icon_smile_sad.gif)