So are you saying when I do the floors I should do spot welds around the panel until it is closed up? i.e. start on left and move in a circle around the panel just spot welding each side to avoid warping.

 

Exactly, you will be able to tell pretty quick how big of a spot or stitch you can get away with once you get started, regardless, you will want to spot it in around it's circumference right from the start to minimize the warpage you are going to have to deal with later.

 

No problem.
Although there is a big difference between properly hidden and butchery. What works for some just doesn't work for others.
Lynn

 

Yes, I am fully aware that a consistent weld will burn through or warp the metal. I should have clarified myself. I actually had troubles with the spot welds burning through.

 

Don't forget about wire lead length. the longer the length from the gun nozzle the cooler the weld. Gun technique and trigger techinque are important to learn while using the mig, don't just try to use the speed and voltage controls.

 

Looks like you got some good advise. I think some one mentioned, it's not "MIG or Flux". With a MIG you can use flux cole wire with no gas, or you can use solid wire with gas. Both are still MIG.

In my opinion, flux wire is for outside stuff. Like building gates etc. Where a breeze would blow away your shielding gas. So you need flux core to protect the weld pool. You want to weld inside your shop with welding gas, not flux. Much better weld, no slag, just better for what you want to do.

I want to agree with what some one else wrote about welding joints. When in doubt, copy what the factory did. That's what I try and do. The outer body panels that are being patched should be butt welded too, with a TIG, not MIG. Or gas welded with a torch. So you get better weld penitration and a weld that is soft enough to hammer smooth. For some reason a MIG weld doesn't like to be hammered on much. It tends to crack right next to the weld if planished. The torch and TIG do not. ...I don't know why.

 

I will agree, that gas would have been at least marginally better than flux core on the heat issue. I prefer to gas weld even beside this point.

I posted a general answer, for more or less general consumption even though I was answering your post. (I should have been more clear)

You would be surprised how many folks are set on "doing things right" by wanting to run a consistent bead all the way down a joined sheet metal joint. This seldom works out well...