[Help with getting the best white undercoat]

Hello Everyone ,   I am wondering if you guys could help me in selecting what best to use as a white undercoat for my minis?  I never really did do white undercoats before but when I did give it a go I used GW's Corax White. The spray came off all dusty and grainy on the miniatures ruining the handful of models (also if anyone has any tips on how best to rescue these  it would be greatly appreciated). Now I am kind of gun shy to use this white paint again , I sprayed when the humidity was pretty low for down south and it was pretty cool outside , so not really sure what happened or where I went wrong. So I am looking into other paints/primers or maybe giving corax white a shot again if i knew what went haywire and how to prevent the grainy texture from forming on the minis. 

Thank you all for looking and any help you can give! 

[Dynamic Painting Log]

Your GUO looks brilliant !! love the dark tones to him , just fantastic !!