weld thu primer prep

oldred · #1 (**permalink**) 10-12-2004, 12:26 PM

When using weld thru primers(zinc based)on lap joints should it be applied to bare metal or an etch primed surface. The instructions are a little vague on this and I am getting conflicting advice at the paint store. This is the lip on a replacement Q-panel and the lip surface has been sand blasted.

astroracer · #2 (**permalink**) 10-12-2004, 12:45 PM

I wouldn't use the weld thru primer. I've never had good luck using it. Always seems to burn off and/or contaminate the weld anyway. Prep your panels and weld them together then soak the seams with some POR 15 or some other rust converter. Let that set up and then prime and paint normally. After the painting is done you can go back and seal the seams or just squirt some tranny fluid in the joints.

BarryK · #3 (**permalink**) 10-12-2004, 01:12 PM

Weld-thru primer is the best thing you can ever use for corrosion as the weld will only burn away where you are welding and the rest stays for corrosion protection.
It should be applied where you grind to bare metal to weld.

Trans fluid has no place in the same place your painting as it is one of the worst fish-eye causers there is! Its also not rust proofing.

flyfisher · #4 (**permalink**) 10-12-2004, 01:19 PM

not to start a quarrel, but I'll second BarryK.

astroracer · #5 (**permalink**) 10-12-2004, 03:08 PM

I'll stand by my initial response... weld through primer will not stop the rust where the welds were made. The welded area will rust 10 times faster then any of the non welded material. You may as well just epoxy prime the seam then weld it... there is no difference. You have to seal the welded area if you want to stop it from rusting... the POR15 or Rust Mort will do that.
As far as tranny fluid being a fisheye causer I agree 100% but I did say to use it AFTER the painting was done. And NO it isn't a rust proofer but it does seep into all of the seams, it doesn't absorb water (it repels it) and, aside from keeping water out of the seams, it allows the seams to drain and dry out, unlike many "rustproofing" spray on coatings which will seal in water and dirt so the seams never dry.
I'm done, now you can argue and Poo Poo to your hearts content...
Mark

BarryK · #6 (**permalink**) 10-12-2004, 04:53 PM

Quote:

Originally posted by astroracer
I'll stand by my initial response... weld through primer will not stop the rust where the welds were made. The welded area will rust 10 times faster then any of the non welded material. You may as well just epoxy prime the seam then weld it... there is no difference. You have to seal the welded area if you want to stop it from rusting... the POR15 or Rust Mort will do that.
As far as tranny fluid being a fisheye causer I agree 100% but I did say to use it AFTER the painting was done. And NO it isn't a rust proofer but it does seep into all of the seams, it doesn't absorb water (it repels it) and, aside from keeping water out of the seams, it allows the seams to drain and dry out, unlike many "rustproofing" spray on coatings which will seal in water and dirt so the seams never dry.
I'm done, now you can argue and Poo Poo to your hearts content...
Mark

******************************************

Who is to argue? We only seek facts here!
WE stand corrected!
You as an engineer (frame designer for GM) we all stand corrected.

Now you tell the idiots you work for to take the weld thru primer requirement out of their warranty repair Manual and I will write the oil company I use to work for and tell them to stop putting "moisture dispersant's in trans fluid and motor oil"
Nothing better than a learning edumacation.
Thanks
BWK

adtkart · #7 (**permalink**) 10-12-2004, 05:33 PM

The parts manufacturers, vehicle manufacturers and insurance companies, all require the use of weld-thru-primer at all welds for their warranties to be in effect. It is also a requirement according to ICAR and ASE.

I guess they never heard of using tranny fluid. Then again, maybe they don't want to be held responsible for the vehicles dripping tranny fluid on the ground.

sevt_chevelle · #8 (**permalink**) 10-12-2004, 05:38 PM

Ive seen tests done that showed HOW important weld thru primer is.
How do you protect the metal sandwiched on a lap joint, you cant apply POR afterwards? Epoxy primer cant be welded over and if you do it just burns way leaving you no protection.

Take some scrap metal weld it up. On one use nothing, on the other just use weld thur on the joint seem. Throw them outside and see which one rusts first

BarryK · #9 (**permalink**) 10-14-2004, 05:21 AM

Quote:

Originally posted by BarryK
******************************************

Who is to argue? We only seek facts here!
WE stand corrected!
You as an engineer (frame designer for GM) we all stand corrected.

Now you tell the idiots you work for to take the weld thru primer requirement out of their warranty repair Manual and I will write the oil company I use to work for and tell them to stop putting "moisture dispersant's in trans fluid and motor oil"
Nothing better than a learning edumacation.
Thanks
BWK

*******************************************
I got an email last night from someone asking if he should use Weld thru or what?
I'm truly sorry to confuse anyone here. the above answer I gave was just a SMART A** one as the statements posted were so stupid I did not think they even needed explaining, so I gave
a stupid answer!
I did not think anyone would pay attention.

Bottom Line is ADKART & SEVT CHEVELLE are a 100% right.
sorry for the confusion.
BWK

astroracer · #10 (**permalink**) 10-14-2004, 07:13 AM

Quote:

Originally posted by BarryK
*******************************************
I got an email last night from someone asking if he should use Weld thru or what?
I'm truly sorry to confuse anyone here. the above answer I gave was just a SMART A** one as the statements posted were so stupid I did not think they even needed explaining, so I gave
a stupid answer!
I did not think anyone would pay attention.

Bottom Line is ADKART & SEVT CHEVELLE are a 100% right.
sorry for the confusion.
BWK

Well Barry, I'm sorry you had to get so personal about this... There was nothing in my post that was "stupid". I was simply stating facts and my own personal experience... I am truely sorry that my opinion is different from yours. Next time I'll wait until you respond and then I'll agree with YOU 100%.
I was just throwing out some suggestions and possible alternatives. If that isn't acceptable to you or the rest of the board I will go away so it will never happen again.
Mark

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