I had the same problem with both the regular Vallejo paints and their Air brand which is supposed to be ready for airbrushing. I thinned and thinned but still had issues ( went from not getting anything out to runs). The Model Master acrylics can be used straight from the bottle without thinning but I typically thin it some after I have used the bottle 2 or 3 times. I'm a firm believer in using the manufacturers thinner