MIG Welding vertical surfaces

vertical gmaw should use short circuiting or pulsed spray method. if youre running smaller wire you can also use spray transfer. it sounds like you were running vertical up and you were either set to high or you werent running fast enough. you can weld vertical up or down with GMAW with equal results. vertical down is typically easier depending upon your level of experience. in the meantime, if you use the short circuiting method your pool will run the coolest allowing you to run a little slower.

Your metal is too thin for vertical up. Run it hot vertical down with pretty small wire, and slight weave.
Vertical up is for metal starting at twice your thickness.

Vertical welding with GMAW is always a tricky thing. You are adding a lot of metal. So, it is difficult.
I, personally have not had a great amount of luck welding GMAW vertical travel up. Since most of the things I MIG are thinner stuff, I just weld everything down. Usually things that are structural and need good penetration are of much thicker materials than 3mm. For the rest, I use downhill. With downhill, you can turn it up and run faster. You can weave. You can make multiple passes, but just don't make several cold downhill passes, or you will not have a lot of strength.
Don't know if this is the right way to weld things, but it works for me. If I have anything that really needs to hold, I crank it up, or if it is thick enough, use 7018. Sometimes you can even reposition the piece.
Steve

Guys,
Thanks for the advice, I'll try some of it out on the weekend.. I'm not really sure what my welder is capable of.. its a BOC 250C.. perhaps its rebadged from something you guys might know..
You can see a photo of it here (and I have no idea what half of this stuff means :-) )
The specs I got from the BOC site are:
Supply voltage (V) 220 - 240 Frequency (Hz) 50/60 Phase 1 Rated primary current (A) 25 Supply fuse (recommended A) 32 Supplied primary plug (A) 15-Limited Output Primary cable length (m) 3 Welding current (Amps) 30 - 250 Duty cycle 30% @ 250A Output voltage 17 - 41.4 Voltage steps 16 Inductance settings 2 Polarity change for gasless wire Yes Remote interconnection cable lentght (m) n/a BOC gun/length (m) MG25i/4 Number of drive rolls 2 Wire feed speed (m/min) 0-18 Wire diameter (mm) Solid 0.6 - 1.0 Soft 0.8 - 1.0 Flux cored 0.8 - 1.2 Wire inch & auto wire load Yes Stitch/spot weld Yes 2T/4T switching Yes Burn back control Yes Isolated electronics Yes Fan on demand Yes Copper transformer Yes
I'll let you know how I go on the weekend..
Cheers,
Duncan. Adelaide, South Australia.