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Old 03-17-2006, 10:13 PM
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Thoughts on weld-through primer?

Hey rodders, Happy St. Patricks Day. I would like to hear what you guys and gals think about weld through primers. I bought a can a few months ago and finally i'm to the panel replacement part on my car and was wondering if its really worthwhile using? Thanks for looking, --Kevin

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Old 03-17-2006, 10:23 PM
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Sure it is, as long as you use it right. Weld thru primer is a zinc rich primer to be applied where panels are overlapped and welded. An example would be a lap weld, where you lay a piece of metal over another and plug weld it thru holes or you put a bead along the edge of the overlying panel.

The area under the lap needs protection, any other paint is just going be burn. Weld thru will burn but it melts back into the weld.

It is not to be painted or primed over, it has VERY poor adhesion qualities. So after you prime an area that will be "trapped" in a lap and weld it, you want to wipe off any weld thru primer that is still showing before you prime it with "real" primer like etch or epoxy.

Don't apply it too thick, and let it flash off well before you weld.

Brian
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Old 03-17-2006, 10:38 PM
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Brian is right on as usual. Use the primer in pinch weld areas or anywhere a lapped joint is used, it shouldn't be on any exterior surfaces because of the limited adhesion and corrosion resistance is has. When installing a panel spray the inner edges of all of your lapped seams, let it dry, weld the panel on. If there's some overspray it can easily be wiped off with a towel and lacquer thinner. When the job is done I try to treat all seams with a cavity wax type penetrating rust coating like 3M's Rustfighter, this stuff seeps into the seams and fills the void with a waxy coating to keep moisture and air out of these rust prone areas. Transtar sells a nice kit with a 360 degree spray wand and includes it for free when you purchase a 6 can case of their spray. Bob
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Old 03-18-2006, 07:33 AM
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Some time back I was asking the same question, I had always just primered the seams lightly (was using laquer primer in those days ) and then sealed both sides, worked ok I guess but after using the weld through (3M) I would never consider not using it now.
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Old 03-18-2006, 08:16 AM
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re: Thoughts on weld-through primer?

Ok thanks, I plan to butt weld all the actual door patches and quarter patches but I'm gonna give it a shot on the new floors and supports. Thanks for all the help, Kevin
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Old 03-18-2006, 05:02 PM
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I like to use

U_POL weld thru primer its the best ive found and i have used most of em .mike
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Old 03-18-2006, 05:38 PM
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buy brush on, you only want it in actual the weld area.....SPRAY CANS ARE LIKE A FIRE HOSE
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Old 03-18-2006, 05:51 PM
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Another tip on weld-thru:

New panels often require fitup, sometimes needing to be put in place and removed several times. Only apply the weld-thru after all fitting is done and the part is being put in place for the final time. That way the primer will not get scraped away from the mating surfaces.
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Old 03-18-2006, 11:35 PM
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Quote:
Originally Posted by red65mustang
buy brush on, you only want it in actual the weld area.....SPRAY CANS ARE LIKE A FIRE HOSE
The brush on is cool, but with 95% zinc it settles soooooo bad. To shake the darn thing up takes forever. What came up with is to take a piece of cardboard and cut a one inch or so square hole in it. I then hold the cardboard up to the area I am spraying and spray thru the hole!

Works like a charm.

Brian
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Old 03-19-2006, 02:58 AM
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good idea Brian...
but I was being "Scottish".....a $30 spray can doesn't go far when you do floors and toeboards (his post purpose)....lot's of linear ft to weld

workingclass....
if you do buy spray....you must shake before every spray...so much solids it clogs the nozzle....and clear the nozzle tube if more than 5 (?) minutes between sprays...
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Old 03-19-2006, 11:21 AM
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Quote:
Originally Posted by red65mustang
good idea Brian...
but I was being "Scottish".....a $30 spray can doesn't go far when you do floors and toeboards (his post purpose)....lot's of linear ft to weld
Red, Red, Red, first off, a can of what brand costs thriry bannanas? SEM, 3M and just about every one I have ever seen except "AUTOTECH" (about $20.00) sells for about ten bucks. And I use this stuff everyday. A can will last me MONTHS hanging quarters and floors and what not. I have a 2006 Prius on my rack right now getting half the floor, both rails up to the rear seat, and the rear body panel. I will be using that same can that will last me MONTHS. And besides, compared to the TENS OF THOUSANDS of dollars spent on these hobby cars, what is $30?
Quote:
Originally Posted by red65mustang
workingclass....
if you do buy spray....you must shake before every spray...so much solids it clogs the nozzle....and clear the nozzle tube if more than 5 (?) minutes between sprays...
Now THERE is a tip of the day!

Brian
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Old 03-19-2006, 12:07 PM
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Brian, ok, a 12oz spray can is $22 or less......a quart of brush on is $15 or less....haven't bought any in a very long time cause I bought a qt, will last me (and my friends) the rest of my life

working class...when there is a third of a can and no propellant, or a half used can with the tube clogged or a half clogged nozzle spraying a stream on a Sunday....hee hee hee "remember Brian"
ha! buy it cheap! "on ebay".....
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Old 03-19-2006, 12:14 PM
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Check out the "Tip of the day" in your name. And read the whole "Basics" if you havn't. I am not kidding, 90% of the aerosols I use I get every drop of product out of them using these tips.

Brian
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