So I am about to start spraying the high build after doing the body work, filling and etch primer. The directions say mix 4:1 for high build and 2:1 for surfacer. I tried a little test spray and the mix seems awfully thick. It barely goes through the gun, and dries really dusty. It is thick though. Is this typical for hb primer. I am using a star gun with a 2mm tip and spray pressure about 300 kPa. I have done a lot of airbrushing in the past with acrylics but I have never used high build auto acrylics before. What's the go with this stuff?

It will be very thick at 2:1. You will need a 2.5mm tip to feed putty. To do it with a 2.0 or 1.8 tip you will need to thin it to primer surfacer.