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Expert
Posts: 1207
 
Location: Ponder, TX | When lap welding new sheet metal to old, what's the best way to prep the surface of the old metal? Even though it's been dip-stripped, there is going to be some surface rust beginning to form. I did some small patches and after grinding to bare metal I used metal-prep before welding, but on larger pieces like the floors, I'm concerned about rust pockets forming in the tiny pits before I get around to priming and undercoating, and in the minor gaps between panels. Is it an issue, or am I being overly concerned? |
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Expert 5K+
Posts: 8445
  
Location: Perth Australia | You can use a weld through primer if you like (I have, but I didnt like it as it seemed to make it harder to weld and the welds were not as "nice").
If you clean the metal well and seal it all up after your done, you should have no problems.
Just remember, when they built the car, they just spotwelded the panels together then seam sealed them and they are (mostly) still here 50 odd years later.
If you are lap welding, I would probably just plug weld it and seam seal it as your going to see the repair anyway if you look for it, if you but weld the panel, then the repair is harder to see, but will have to be fully welded
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Elite Veteran
Posts: 1102
Location: Hayward, Calif | Like ttotired said, I also tried weld thru primer and was not impressed with it either. I have done butt, lap and plug welding also, depending on where I was doing it. It kinda depends on what and where your welding and how much room you have to work with. I found butt welding works good when leaving a slight gap with a piece of new metal in behind to absord some of the 'puddle' and strengthen the weld. Copper heat sinks are a must. In some occasions where I couldn't use a clamp I used magnets to hold these pieces in place. Magnets don't like much heat and will shatter. I lap welded my lower rockers just below the door jam and on back to the rear wheel well. Cleaned it up real good, applied body filler over the weld and sanded down smooth. Shot some primer over it and the repairs are unnoticable. I did all 3 weld types on the floor and the trunk floor and covered the seams with Auto Body Sealer. Comes in a tube. Get it at the paint store. I use Rust-Seal on those lightly rusty areas where I need to weld to it. Again, clean it good and prime it. Jerry |
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Expert 5K+
Posts: 5006
| I only butt or plug... lap welding you are just asking for trouble and it sloppy. |
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Expert
Posts: 2524
Location: Houston | The factory used lap welds in many places, so it's hard to condemn them especially if you are aiming for originality. Plus, there are places where a but weld would be very weak. For example, the rocker panels are made of two pieces that are lap welded at the bottom...this would be much weaker if it were butt welded. Similarly, the entire A pillar area (or whatever you call the area behind each kick panel, behind each front wheel) is lap welded and could never be butt welded.
If you mean butt welds in areas where no factory seam ever existed, such as a floor pan patch, I could agree on butt welds. But then again, in 2014, a cleanly done lap weld will last the next 75 years (long after we are all dead) and is actually stronger. It's not like these cars are seeing the daily-driver-park-it-in-the-rain-every-day kind of duty they used to.
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Extreme Veteran
Posts: 380
Location: Kennewick Wa | "It's not like these cars are seeing the daily-driver-park-it-in-the-rain-every-day kind of duty they used to."
mine will |
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Expert
Posts: 1207
Location: Ponder, TX | The lap welding I was referring to in the original post is mostly in the floors and trunk, not exterior patches. I have no concerns about new metal against new metal, only where old meets new. Grinding the old to eliminate every spec of rust pit makes the metal too thin, so I only grind enough to make a clean area for the weld.
I'm not going to worry about it anymore. The car will be driven daily, but not in bad weather, so I know it won't rust out during the time I have left. |
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Lap Welding Metal Treatment
