After butt welding my trunk in then grinding down the welds I can see a number of little pin holes when I put a bright light in the trunk and crawl under the car. My question is: Will I be OK to use a fiberglass filler over the welds (I have Evercoat Tiger Hair to use for this) or should I go back and weld all the little pin holes and grind again. :(

Trooper

Go back and weld up the pinholes. If you don't you run the risk of moisture getting between there and blistering will occur.

Agreed. Try to weld them up.

Sounds like you welded the metal without cleaning it propperly or you welded it without argon gas.Did you mig or tig it? The wind may have blown away the gas leaving the weld exposed to oxygen which causes holes (porosity)You can use brushable seam sealer to cover the holes & make it water tight. All automotive paint shops carry it.VERY easy to use.

Thanks guys,
I just love to spot weld for hours grind for hours then do it all over again smile.gif Hopefully this second time won't take as long.

Trooper

Turn down the welder, it will help not to make those holes bigger.

This was my first try at welding sheet this thin. I initially thought I needed to spot then move then spot then move ect.... About 1/2 way through I found that I could easily stitch about an inch at a time with repeated spots then move without getting the metal too hot. Those welds went down much better with much better penetration and no holes. Hopefully next time I will have a lot less problems.
I think what I'll do is flip the car on the rotisserie and fix the pin holes from the bottom since I haven't ground that side down yet. This should make it easier to see the holes and decrease the amount of interior grinding. Will this method be OK?

Trooper

You can talk about perfect welds all you want, but to get a perfect waterproof weld seam, especially for any length to speak of, is damn near impossible IMO. And if you're not a pro, forget it. One, ONE pinhole will let moisture through to the plastic filler (not waterproof-like a sponge) on the exterior. IMO you must put a layer of water RESISTANT resin on all welds before the filler. Yes I know the resin fillers aren't 100% waterproof, but much more so than plastic filler. They (resins) work pretty good on boat hulls.

Von,
I'm using Evercoat Glass-Lite. It's a polyester resin filler with short strand fiberglass in it. It says: Rustproof and Waterproof. For weld areas and bond lines. Ideal for rust repair and filing holes and cracks in metal. On the back it says: For repair of weld areas and bond lines to prevent stress cracks and repair mapping. Does anyone know what mapping is?
It also says it can be topcoated with any evercoat lightweight filler. I bought Rage for this.

Trooper

Msperformance,
The trunk was new. I cleaned the paint off both sides with 40 grit roloc on a diegrinder then prepsol before welding. I use a mig welder with 75%argon/25%CO2 .023 wire. The welding was done inside (no wind). The holes were where many of the spots butted up to the next spot. The welds look similar on both side of the metal. I was told this means a good weld with good penetration.

Sevt,
I think I got the heat pretty close I only had 3-4 blowouts on the whole trunk and was able to fill them in simply by drawing the nozzle about a millimeter furthur away from the metal.

Thanks for the tips guys.

I'm pretty sure most of my problems with pinholes were more human error than the hardware. I just wasn't butting one weld tight to the other. I have done quite a bit of welding but never on 22G sheet butt welds with no backing. The stop and start welding is what caused my problems. All in all I think I did OK.

Thanks again,
Trooper

Any other tips or comments are greatly appreciated.

in my own amature expiriance using a good heat sink keeps me from blowing holes. I have my own little set including a cannon ball cut in half, piston pin from a cummins truck, a 1/2" steel dowel rod, a heavy piece of sheet metal, and a spoon. hope this helps.

Trooper if you welded a 1in seem its a pretty long welded seem in one shot IMO in 22ga. The most I would go is 1/4in.

What I do is take a grinder and cut down the weld bead that I will be welding into when I connect two welds together. This way you get more peneration into the base metal instead of the weld bead that will just get ground down later.
This really helps on the skip welding process, as the startup heat is the MOST important. If you remove some the "waste" bead you will get a more localized heat area resulting in better peneration of the base metal and the connecting weld.
Make sense?

sevt,
Makes good since. That shoud also keep the arc from starting on the top of the previous bead. Good advise.
Your right 1" is a pretty long weld. It was probably closer to 3/4". The way I got by with it was placing about 6-8 consecutive spots instead of one continuous bead. It did get warm. I don't think I would try it on a body panel but the trunk turned out ok without warping.

Trooper

Where are you welding, and can you reach the back side while doing it?

When I weld sheetmetal, I (if possible) hold a thick piece of brass (pipe fitting) against the back side. The weld will not stick to the brass, so you'll have a flat weld on the back side. The brass absorbs much of the heat, and reduces warpage. I also never get blow-outs while doing it that way.

In many cases, though, you simply cannot get a piece of brass back there (can't reach, something in the way, or double-paneled)

You need to learn the technique "hammer weld". When welding a panel to something like a cross member (using Mig weld here), apply the weld and immediately (or as quickly as feasible), tap the molten weld with the round head of a small ballpeen hammer. It flattens the weld out and eliminates the air pockets. Very easy to do. If you have a good weld to start with, the result is even better.

Make absolutely sure the metal is clean before welding to avoid blow throughs and pinholes. The metal needs to be clean for your puddle to flow, etc. Spot, spot, spot instead of running beads if you're having trouble controlling a bead. Some welders are much more tunable than others which require different techniques. Practice makes perfect.

where I get the holes in where two stitches adjoin each other. I also always thought that the welding expanded/stretched the metal but was recently told it actually shrinks it. I've watched some good body guys use a quick cooling with a rag technique while welding. I assumed this was to shrink the expanding metal. I'm :confused:

I thought heating=expansion and cooling=contraction.

I do know that in a t-weld, the weld pulls towards the side it's on. Contraction of cooling pulling it over? :confused:

Ah, science. graemlins/clonk.gif

Yes when you heat metal it expands. BUT during welding you are heating up a small area of metal, also keep in mind that heated metal is also softer as well. The heated metal expands outward but the cooler much stiffer surrounding metal keeps it from expanding. The heated metal needs to go somewhere so it bunches up.

If you cool the weld with air or water you can actually shock the metal into staying in that shrunking mode. The metal is hot and shrunk then you suddenly cool it, it causes the metal to remain that state.

But if you allow it to cool naurally the metal or most of it will return to its former state.
Cooling the weld makes the metal remain shrunk and also makes it brittle. So cooling is a bad idea...Eric

My welding instructor told me to start a half inch away from your old weld or however long you want your bead to be and then weld back to the old bead that way by the time you weld up to the old bead your are much hotter than when you first take off and you can burn into the old bead much better. It has helped me allot!

zachscc has the right idea. You're never supposed to start a new weld on the end of another bead but rather like he describes. You can also start just a little away and then go back into the existing bead and then go in the other direction again. This is more of a technique for heavier metal though. In either case, you want the arc fully started and hot before you hit the existing bead.

Peter