Step by Step
Door Rust Repair

Using the backing strip method

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1. This is the exterior of a truck door that has be ground down to reveal  major rust problems.  We've taped a straight line just below the peak to guide a nice straight cut.

2. We do most of this type of cutting with a small angle grinder and a good cut-off disk.  We can get fairly accurate and straight cuts using this method.

3. You can see, after the tape is removed, that we have a nice straight cut.

4. After the top cut we grind the bottom and side edges to release the panel.

5. You can see how grinding the edge releases the metal we want to remove.

6. The door is now flipped over and the remains of the outer panel are removed.  In many cases this can be done by prying the strip off the jamb metal but in some cases it needs to be ground or drilled to prevent damage to the jamb.


7.& 8. After the jamb metal is exposed it should be sanded to remove lose rust then treated with a rust converter one the edge of the jamb and also inside the door.

9. Preformed door bottoms are a standard repair part for this type of repair.  Notice the small bend at the edge.

10. The new metal is place so that it's aligned properly then marked to cut for butt welding.

11. Again a piece of tape can be placed on the metal to mark a straight line for cutting or you could mark it with a pencil.

12. This time we cut with an electric shear because it makes a nice straight cut that is very clean on both sides.

13. Here the new metal is shown after the cut.  We'll be using both pieces since the strip we cut off can also be used as a backing strip.

14. Holes are punched along the edge of the remaining door panel.  Since the metal strip needs to be fastened FLAT against the inside of the metal it's best to punch and not drill since drilling causes the metal to dimple and hold the metal away.

15. Care needs to be taken so that the underside of the metal is clean and won't hold the backing strip away from the new metal.  Here we are filing off flashing left by the die grinder.

16. The backing strip is cut to the proper length and clamped so that the strip can be welded through the holes.  You can't have too many clamps.

17. When welding the strip we start in the middle then weld half way to either end then the ends then come back and split the distance between welds by jumping from place to place.  This eliminates any heat distortion from being too severe in one place by spreading it over the entire length of the repair.

18. Here you can see how the "plug welding" leaves the edge of the backing strip nice and clean and ready for the new metal to lay on top and be butt welded.

19. When the new metal is laid in place you have a little play because the bottom can move a little to accommodate a good tight fit at the top.

20.  The new metal is butt (spot) welded using the same pattern as the backing strip.  We start in the center then half way to the ends then the ends.  We then split the distance between each weld jumping around until the welds are about a half inch apart then we weld the seam solid.

This method will cause the weld to NOT be as pretty as it would if you just ran the weld from one end of the panel to the other but the heat distortion is much less and you still get a good solid weld.

21. When tacking the new metal in place we push it into place with a rod that fits between your shoulder and the metal making it easy to push into place.  Care needs to be taken that you don't push too hard or you could weld low spots into the panel.

22. As you can see the weld isn't pretty when it's done in this manor but there is very little heat distortion in the metal.

23. Grinding the weld will level it but be sure not to grind too long in one spot or you could cause heat distortion.  Grind on one area then move to another before the metal gets too hot.

24. After the metal is ground level the seam is almost invisible.

25. The door is now flipped over and the new metal is trimmed so that the ends can be folded over the jamb.

26. A hammer and dolly are used to pinch the new metal onto the jam.

27. Corners can be ground to the proper shape and welded.

28. I usually apply a half dozen tacks along the bottom of the door.  Welding solid isn't necessary.

29. Don't get carried away with welding the jamb to the new metal, tacking is all that is necessary and too much welding can cause heat distortion on the front of the panel.

30. After a light grinding (if necessary) we brush on a coat of epoxy primer on the bare metal.

31. Flipping the door back to the front side we apply a moisture resistant filler over the seam.  Then a regular body filler to finish the leveling process.

32. Seam sealers are applied inside the door as well as were the new metal wraps around the jamb.
We use single part urethane sealer on the backing strip and on the exterior bottom seam but we also use a two part self-leveling seam sealer on the bottom, inside seam because it helps seal the this area better than single part products.

Make sure all drain holes are left open so that moisture doesn't collect in door bottom.

33. The door has been painted on the inside prior to installation.

34. The exterior of the door is primed and guide coated prior to installation.

35. After the truck is painted the door looks great.

36. Because we cut below the peak we left the lines nice and straight.  You would never know it was repaired other than the entire truck looks too good.

The best method of rust repair is replacing the metal as show above but if welding in new metal is not an option you can see an alternative method HERE.


Disclaimer: The ideas and methods described in this web site were developed under unique situations. Since these situations cannot be duplicated, you may get different results. Use and application of any of the site's content is at the user's own risk.

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