Originally Posted by
Fat Boy
If I were dealing with 'ugly' tig welds, I'm not sure I'd be completely at ease riding the bike. That hints at severe undercutting or lack of penetration. If you have a problem with seeing a tig weld in general, then you've got weird mental issues. A nice tig weld is a thing of beauty and I can't understand why you'd want to cover it. Filing hurts the grain structure and is a no-no even if it ends up smooth. It may not make it break, but it will make it weaker.
If you absolutely have to cover the weld, body filler(Bondo brand sucks, but would work) and/or spot putty is probably the way to go.
If JB Weld is the answer, then it was a stupid question.
Many of the cheaper steel frames have functional but lumpy TIG welds. Taking a rat tail file and dressing down the chunks sticking up is a perfectly safe thing to do. There is no harm that will come of it as long as you don't go very deep into the weld and stay off the tube itself as much as possible. Undercutting is something that happens on fillet brazed frames when the builder cuts into the tube too much while dressing down the fillets. Needless you don't want to do this. And the grain structure will not be altered by dressing the welds.
After dressing down the lumps, filling any valleys with JB Weld is a good idea; it's just a cosmetic dressing so no worry. JB Weld itself is pretty good stuff. Lots of framebuilders use it to attach carbon stays since it's strong and not brittle.