Replacing bottom door skin

[Mercury100]

I have the typical front and rear outer door skin rust. Inner door is fine.
With the replacement bottom door skin where is the best place to weld in the seam?
Above the bump?
At the top of the start of the bump?
At the tip of the bump?

[cep62]

Without seeing your door , I always try to keep it as low as possible.
If your rust goes over the bottom body line it depends on the condition of the door.
maybe in the bottom side of the bump , you have a couple inches of space and the bodylines give some strength to avoid warping.
(it'll still warp some)
I would butweld the outer edges and overlap the middle with a 1/4 - 3/8 lap weld.
weld short welds and cool with an air hose , take your time fitting and welding

assuming you're using a mig welder

[Ranchero50]

I would make the patches as small as possible. I tried to replace the lower half, cut at the bump and ended up with a junk door instead. Weld wasn't an issue but rolling the edge over didn't go as planned, at all...

[Jsimon]

I'm doing the same repair soon, am considering spot welding a piece of 2" sheet metal the length of my cut on the inside so 1" is exposed then using body panel adhesive and a couple spot welds to join the door skin. Then filling the seam with body filler.

[cep62]

I'm doing the same repair soon, am considering spot welding a piece of 2" sheet metal the length of my cut on the inside so 1" is exposed then using body panel adhesive and a couple spot welds to join the door skin. Then filling the seam with body filler.

The one drawback to that is now you in effect have a water trap in the door even if you don't have it in the rain , on damp days moisture still accumulates and rolls down and can cause rust.
you might be able to seal it from the inside.
but as a rule of thumb you want to place your patches like shingles so water rolls off the seam.

[jzjames]

My “ghetto” fix for my bottom doorskins;

I had the rustouts in the bottom corners of each door. I bought the 9-inch bottom doorskins and they came in pretty good except I did have to hammer the widths a little to match the width of the door. Then I carefully cut out and separated the bottom metal from from the inner door metal and fitted the repair panels to my liking.

I OVERLAPPED the the top horizontal edge onto the door about an inch and used 3M panel glue. Pop riveted the overlap together, waited for it to cure, and then grinded off the pop rivets.
Finessed a skim of bondo over that seam on the outside of the door. (I pushed the sheetmetal in a little to make it look flush). It came out decent.

Now the kicker.
Since the water still drains to the bottom of the inner doors, I knew the rust and rot would soon be coming back, so I got my hands in there and was able to smear in a good thick coating of Blackjack Roofing Tar - - to cover the entire bottom area of the inner doors - all the way up and over the overlapped seam of the repair panel. All the way into the corners. I made sure the factory drain holes of the doors were open. And a laid a coating of the tar on the bottom OUTSIDE on the line of the drainholes.

My truck sits outside in the Washington rain all year round, the water pours into the doors, drains out and never comes in contact with that bottom area sandwiched metal. The doors look good year after year,