I had a few holes in the floorboard, nothing real big (Average Nickle Size) however I been welding pieces of sheetmetakl to cover them holes, but most of the time the mig just burn through the metal and floorboard. I have the setting down on ONE and speed set to about 3. Also is it feasable to put fiberglass over the holes once im finish? Will the fiberglass crack from body flexing. What is the best body filler to use on the bottom side of the weld on the under carriage.
Thanks:
David

 

If the metal has thinned from rust eating at it or you're trying to make a solid (continuious) weld on such wimpy gauge metal, you'll want to (my opinion) stitch (or trigger.. whatever term you like) weld the piece in to keep it from getting to hot & melting the surrounding metal and the patch piece (which is more prone to meltdown).

I also wouldn't (personally) worry too much about the looks of the underside (ie, fiberglassing or using bodyfiller.. neither holds/seals out moisture anyways). Just make sure the surrounding metal is nice & as clean as you get it (wire wheel, soft grinding disc..) and, if your patching from the topside, use some body seam sealer around the perimeter of the patch/overlap area. Let that dry & put some undercoating on it & you'll never know it was there. That's just my opinion.. I could be wrong.

 

i personally would use a grinder with a cut off wheel to cut out about 1/2 inch past where the rust stops, and weld in a piece from the top using the previous posters spot weld method, welding very little at a time and letting it cool before moving on. then just place the carpet back and your good as new, no one would know from being inside your car, and someone who gets it on a lift and sees it, who cares. what can they do, if they say something, just look at em like they are stupid and say "so what"