As this came up in a forum thread, here is a little warning and/or let's have a laugh at my misfortune  

This is obviously not a 40k model, but it serves the purpose, because it's what I used. 

Finished my faction terrain piece for AoS, and as I was going to be handling it a lot, I thought I'll varnish it with my Citadel Munitorum Varnish Spray. 'What could go wrong?' thought I?

Well, the results speak for themselves. 

Yeah. It went all frosty. So I've either put too much on at once, it was too humid, it was too cold, the can is a couple years old, I might not have shaken it long enough (it needs longer than paint) or a combination of all. 

I almost defintely put too much on at once I think. Probably didn't shake it enough either. 

Anyway, let this be a lesson and warning to you all! Make sure you do it properly, and maybe test it out first when you are going to use it, or suffer the consequences like I did