Hi,

I'm using Vallejo for some while so I will try to help.

1. They have coupe of lines of paints. Game Color which is for painting gaming figurines (it doesn’t rub of so easily). Model Color which is generally for modeling. Air Color which is thinned up version of Model Color ready to use for airbrush. Game Color and Model color are rather thick inside and it has sometimes consistency of past which is good cause you get more paint for less money as you can thinned it.

2. If the surface isn’t prepared surfaced or sanded this paint unfortunately doesn’t stick to good.

3.  It is better to use some kind of primer it even can be some other paint that sticks well to the surface.

4. Vallejo are water based paint so for thinning them (Game Color, Model Color) you can use tap water but it’s better to use dematerialized water as the paint has better properties then when you use regular water and you can easily add to the mixture retarder. If you want to thin Model Color or Game Color paints for air brush I found by experimenting that using water then some Tamiya thinner makes wonders. It goes easily thru airbrush and doesn’t run down on model. As the paint has different thickness I can’t get you the ratio so you just need to experiment.

I hope I help at least a bit.

Cheers