Hope this helps
First we apply the base color. In this case I used Model Air Colour, but any other paint will be a good base for the hairspray technique.
Next we apply a thin, but even layer of hairspray. Some modellers apply the hairspray through the airbrush to get better control. I usually mist the hairspray from a good distance straight out of the can. The brand is not important, so far any brand worked fine.
Then we airbrush a random coat of white, depending on the effect you would like to achive. In this case I was after a rather worn off finish.
Now we can remove the white paint again, by using a brush and water. You might want to try out all the effects that can be achieved with different brushes, toothpicks etc. The water will solve the hairspray and the acrylic paint will start to lift after a few seconds.
Since the effect of the chips can be a bit harsh, drybrushing in the base coulor will further blend the effect a little more.
Here's the finished model: