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Old 04-15-2010, 12:45 PM
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welds rusting

I have been using a MIG for a good few years now and most of the welds happily sit in bare metal in my workshop for a few months without any signs of rusting before preping and putting epoxy on, but recently some of them have gone rusty within days.

Is there any reason why a MIG weld should start to rust quickly? And is there anything special I should do to prep for paint - it is my car and I intend to keep it for a long time so the paint job needs to look good for a long time.

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Old 04-15-2010, 01:25 PM
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IDK why some might rust and others don't, but ideally we should clean up and prime out bare metal right away, even though I am guilty of not doing this a lot.

I recently moved to Arkansas (virtual rain forest!) from the DESERT. While in the very dry desert (8" annual rainfall) I could be lax with covering bare metal most of the time, and indeed I still have some parts of my car in bare metal from before the move, but I have it stored in a dry place where temp swings are not big so I have thus far largely avoided the rust monster, which has surprised me.

Perhaps your parts are in a spot where temperature variations throughout the day and night add to condensation?
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Old 04-15-2010, 03:56 PM
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warm days with cool night cause condensation on metal
i use pickle-x on welds or sandblasted parts that i won't be able to paint right away
http://www.picklex20.com/
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Old 04-15-2010, 07:46 PM
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Try using a self-etching primer that you can spray on the welds after you mig weld them. If you grind the welds down, re-use the etch primer to keep rust from forming.
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Old 04-16-2010, 03:34 AM
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Parts of this car have been in bare metal for about 10 years with no rust, it seems strange that doing some MIG welding a few days ago caused alot of rust to form after on them and immediately next to them. I know the UK does not have the best climate but it is in a insulated heated workshop. Just curious, wondered if the MIG process caused carbonic acid or some such reaction to take place.



The car is being fully preped before paint and most of it is now in epoxy.
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Old 04-16-2010, 04:58 AM
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I accidentally found out that the mig wire is pretty much all made in China these days.
My problem was with the spool coming apart on a new roll I brought it back and found out that its hard to find US made wire anywhere.
I'm not sure if your problem starts there or not maybe you have some moisture in your tank...
sometimes if a tank sits for a long time the mixture separates and you have to roll the tank on the ground.
My old welding teacher told us that, but I've never had to do it...it might just be with acetylene,not to sure.
interesting problem ,I wouldn't worry to much about it though.
I'll bet "old red" would know
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Old 04-16-2010, 06:49 AM
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Quote:
Originally Posted by deadbodyman
I accidentally found out that the mig wire is pretty much all made in China these days.
My problem was with the spool coming apart on a new roll I brought it back and found out that its hard to find US made wire anywhere.
I'm not sure if your problem starts there or not maybe you have some moisture in your tank...
sometimes if a tank sits for a long time the mixture separates and you have to roll the tank on the ground.
My old welding teacher told us that, but I've never had to do it...it might just be with acetylene,not to sure.
interesting problem ,I wouldn't worry to much about it though.
I'll bet "old red" would know
Not sure CO2 and Argon can seperat as such. It is an old bottle and need to be refilled very soon so that may be something to do with it.

It is not causing a problem, call it curiosity. I have never seem welds do this.
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Old 04-16-2010, 08:12 AM
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Quote:
Originally Posted by alittle1
Try using a self-etching primer that you can spray on the welds after you mig weld them. If you grind the welds down, re-use the etch primer to keep rust from forming.
IMHO not a good solution, etch primers have their own set of concerns, just do a search in this forum on etch primers. The overall best solution is to clean the new welds real good then epoxy prime for maximum protection.

Vince
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