Thinning Vallejo Polyurethane matt and satin varnish

[Simon Cornes]

That's it, in a nutshell - what do I use? Being water soluble to clean brushes, etc you would think water is the solvent but I tried this last month with the satin varnish and it reacted badly and kept blocking the airbrush. Luckily I had some Alclad satin and that went on like a dream! But it must be 'thin-able' so what should I use? I'm spraying on top of enamel by the way. Your answers would be appreciated as I want to put a coat of Vallejo matt on tonight to finish a project!

[Space Ranger]

Regardless of brand or type of paint, it's always a good idea to use the manufacturer's thinner. I fail to understand why modelers invest hundreds of dollars in airbrush equipment and paint only to skimp on thinner. It's simply not worth the few cents saved.

[Simon Cornes]

You are so right but I’m not sure which one to use as this is polyurethane varnish, not acrylic and aren’t Vallejo solvents for use with their acrylic paint? 
 

As it happens, I used tap water earlier today with the Matt varnish 27.651 and it worked beautifully but when I tried it with the satin varnish 27.652 a month or so ago, that’s when it all went pear shaped!!