Pinhole Remedy After Welding Sheetmetal Patches?

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dibbons

dibbons

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After replacing rusted areas (floor pan, bottom of doors, bottom of quarter panel) by welding sheet metal patches I find that after grinding down the welds, minute pinholes are in the welded area. What does everyone do about those tiny holes? Thank you.
 
Many ways,fiberglass filler is my preferred method.
 
It needs to be sealed,just like the bare metal as well.
 
Just mix some fiberglass resin up, and brush it in there.
 
72bluNblu said:
Weld them. Fiberglass and metal don’t mix.
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Bullshit, I don't know where you heard that from, but fiberglass is an insulator when there are two different metals touching each other, to prevent corrosion.
 
If your getting porous welds you need to clean the metal better before welding. Also make sure your using enough shielding gas.
 
I believe some tiny pinholes are inevitable. I think (not sure) closing pinholes with more weld may just leave other pin holes (I don't weld, so a little ignorant here, just my observations watching others).
 
I have used mar-glass and kitty hair, long strand and short strand.
Some is harder to work with, but i put it over almost every patch i have welded and it holds well.
24 grit discs work best to give it good tooth to hang onto.
 
Also a solid copper block for backing where its thin will help.
I use a block when welding holes shut. It takes practice to get patches welded in with no pin holes. If its an issue, better off with a lap joint than a butt weld.
 
the putty that they seal the seams for floor pans and trunk pans work great, think about it when you remove a entire floor pan it has a bead all across the back and all the way down the front, and we all know what a pain in the *** it is to grind all that crap out and be able to drill the spot welds
 
sireland67 said:
Bullshit, I don't know where you heard that from, but fiberglass is an insulator when there are two different metals touching each other, to prevent corrosion.
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There is no place on these cars where two different metals touch each other and need to be insulated between the layers. I can't think of a single legitimate reason to use fiberglass to repair metal on one of these cars (replacing a whole panel is a different story). These cars don't use rivets or bonded construction, and we're talking about using fiberglass to cover metal repair that's been done poorly/incompletely.

Other industries and applications are different, aircraft are a completely different ball game. Multiple layers, insulated panels, etc, are a different story. But none of that is relevant to this application.
 
I tried about every process their is and yes pinholes are inevitable. I had best success with tig, and used silicon bronze to fill pinholes, works great. You can see the bronze spots all over these panels.
rust repair 002.JPG
 
dibbons said:
I believe some tiny pinholes are inevitable. I think (not sure) closing pinholes with more weld may just leave other pin holes (I don't weld, so a little ignorant here, just my observations watching others).
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Well that would have been a real problem when I welded up a big hole in a trans pan.
Cleanliness, temp, wire type and shielding gas is the solution.
When I weld something like that I put gas or lacquer thinner in it afterwards to check for leaks, since they both will show any leaks right away.
 
72bluNblu said:
There is no place on these cars where two different metals touch each other and need to be insulated between the layers. I can't think of a single legitimate reason to use fiberglass to repair metal on one of these cars (replacing a whole panel is a different story). These cars don't use rivets or bonded construction, and we're talking about using fiberglass to cover metal repair that's been done poorly/incompletely.

Other industries and applications are different, aircraft are a completely different ball game. Multiple layers, insulated panels, etc, are a different story. But none of that is relevant to this application.
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Just put a thin layer of fiberglass resin, paint it on with a small brush.
It will seal any pin holes that you cannot see, and it will not react with metal.
 
mopar head said:
I tried about every process their is and yes pinholes are inevitable. I had best success with tig, and used silicon bronze to fill pinholes, works great. You can see the bronze spots all over these panels. View attachment 1715191549
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I bought some silicon bronze rods to try with tig.
It didn't work for me so good when I tired it.
But that's probably my tig welding.
I'll try again someday.
 
TrailBeast said:
Well that would have been a real problem when I welded up a big hole in a trans pan.
Cleanliness, temp, wire type and shielding gas is the solution.
When I weld something like that I put gas or lacquer thinner in it afterwards to check for leaks, since they both will show any leaks right away.
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Exactly. All kinds of stuff is welded that has to be air tight, fuel tight, even pressurized at high pressure,. Fuel tanks, propane tanks, oil pipelines, etc, it's a long list. Pin holes are not inevitable.

sireland67 said:
Just put a thin layer of fiberglass resin, paint it on with a small brush.
It will seal any pin holes that you cannot see, and it will not react with metal.
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That's exactly the point. It doesn't react with the metal. It literally will not mix. And if (and WHEN) it leaks, moisture gets behind the repair and it rusts out. The metal on these cars flexes, the resin will separate, and the repair will fail.
 
adriver said:
I bought some silicon bronze rods to try with tig.
It didn't work for me so good when I tired it.
But that's probably my tig welding.
I'll try again someday.
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Some guys swear by it and only use it. I like the strength of steel rod and just use the bronze for pinholes. But I`m talking butt joints, lap joints would probably work great, one plus of the bronze is it`s not going to rust on ya.
 
mopar head said:
Some guys swear by it and only use it. I like the strength of steel rod and just use the bronze for pinholes. But I`m talking butt joints, lap joints would probably work great, one plus of the bronze is it`s not going to rust on ya.
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The only problem is once you’ve brazed it you can’t weld on it again because the braze melts.

Which might not be a problem for you at all. It only comes up up you have to fix something that has an old repair.
 
72bluNblu said:
The only problem is once you’ve brazed it you can’t weld on it again because the braze melts.

Which might not be a problem for you at all. It only comes up up you have to fix something that has an old repair.
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That`s why I only use it for pinholes, once ground flush it`s not as strong as steel. surprisingly I welded through it not realizing it was there, it burned through rather well, unlike welding along realizing your running into lead. Whole nother matter. Lol. No matter how much you clean both sides of this old 40-60 year old auto sheetmetal your bound to get some pinholes, and the bronze works great. Lay 1/16 rod with tig right over the hole, with the current about 5-10 amps hotter and melt a small blob, hit the pedal full tilt and watch it sink in and no pinholes after you get off of it. you`ll grind more weld of the back side than the front. To each their own, use what works best for you.
 
Pinholes are a sign of porosity. Porosity results from inadequate prep, lack of shielding gas, and poor technique. And no matter what you do afterwards, e.g. JB weld, fiberglass, silicon bronze, its will eventually begin to corrode because the porosity will, always does trap moisture.
 
Just mix up some 2-part panel bond adhesive and smear it on with a bondo spreader. Half of all new cars are put together with the stuff, it is made to adhere to bare metal.
 
It is true panel bond is used in new cars, but those new cars don't come from the factory with weld porosity. And I can absolutely guarantee you a heavy viscous material like panel bond will not fill those minute porosity holes. And heaven help you if it is piping porosity, we haven't even talked about the structural strength of a porous weld.
 
We aren't building a 100 story skyscraper here, and the welds don't have to be x-rayed. Panel bond will fill those holes, and it will do it very well. It's even sandable and paintable if need be.
 
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