This, together with the Micro-Mark seam scraper, is one of my most valuable assets. Plastic putty can be used for almost everything. It really shines when you have to fill those nasty joins in warped kits. Of course, you could use Kneadite (green stuff) or Milliput. But that means 5 minutes of kneading and 10 minutes of wrestling with it to go where you want it and not where you don't want it.
Tamiya makes a putty as well. It has more "tooth", but it also requires solvents to thin and remove. Which is a downside. The Vallejo putty is water soluble, and in order to remove the still wet putty you just dab a Q-tip in water and wipe it off. A definite win.
One of the other uses for plastic putty is to quickly add volume to something. In this case I've demonstrated on a dozer blade for a Hellhound.
You can of course use plaster of paris together with the pigments in order to bulk it up. But the benefit of using the putty is that you can remove it without damaging your paintjob. Since you put it on BEFORE the paint! ^_^.
|In just three-hundred easy steps you can go from grey to rust and mud coloured!|
Using pigments over the putty creates some sort of "micro structure" on top of the rough structure created by the putty – that is if you've worked it enough – creating a pretty convincing 3D-effect without much effort.
You can order Vallejo putty almost everywhere. I prefer the one that comes in a tube instead of a bottle. But it's still the same stuff, the tube based putty is just easier to apply. YMMV of course.
Happy puttin' :)