Why can I see my welds?

J

JoeMan

Welded a partial quarter on a GTO, epoxy over metal, then evercoat short strand over welds, filler then glaze... Epoxy over filler work, then poly primer... Blocked down, epoxy, then surfacer... Epoxy sealer then paint... Wetsand very aggressively and buff... We can now see the weld bead very faintly... What gives?
 
You say the weld bead is visible however there should be no bead left if the weld was ground down properly. The welds should be invisible to all but the most trained eye before any primer goes on.
 
If the weld wasn't ground flush you'll often see it show at different temps, I think it has to do with expansion and contraction and more heat radiating from the thickness of the weld. Do you see it in the sun? When cool?
 
What about weld depressions, such as with oxy/acetylene welding? With filler, do these tend to show up later in the finished paint expanding and contracting in the sun?
 
Haven't been in too extreme of temp differences, early winter when we welded, now hot as blazes summer after cut and buff they show... Had to refine an area on the same quarter so we hit the weld spot and it looks good agan... Curious if it will show again, or only if in cooler temps since cut down (again) when warmer... Even before they were very faint... More concerned about prevention... Will have to look at progress pics to confirm, but I don't believe they were so ground that u couldn't tell without detailed inspection... So what about the back side of the weld... Does a guy need to grind that too as to not hold heat in the extra metal from the weld?
 
I am not a pro-anything but taught myself to use a MIG welder and 4" grinder.
If you can get the welder set correctly so that you have proper penetration and flow there will be next to no build up on the under side.
This quarter panel was welded about 3/8" from the door jamb edge and then ground flat using a 60 grit sanding disc on the 4" grinder. Its not perfect but I am definitely getting better with more practice.
As you can see there is virtually no seam or bead to deal with.

 
JoeMan;29759 said:
Haven't been in too extreme of temp differences, early winter when we welded, now hot as blazes summer after cut and buff they show... Had to refine an area on the same quarter so we hit the weld spot and it looks good agan... Curious if it will show again, or only if in cooler temps since cut down (again) when warmer... Even before they were very faint... More concerned about prevention... Will have to look at progress pics to confirm, but I don't believe they were so ground that u couldn't tell without detailed inspection... So what about the back side of the weld... Does a guy need to grind that too as to not hold heat in the extra metal from the weld?
Click to expand...

Another thing to consider-was the seam welded completely? Was this panel only partially welded? I've seen people attach half quarters with a lap joint and only tack welds every inch and these types of seams always show after some time. Usually penetration showing on the backside doesn't produce a large enough bead to become a problem if left as is without grinding. A copper backer during the welding helps lots to control buildup on the backside especially if you end up chasing some burn through holes.
 
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