I have documented my method for repairing hoods. While not an expert in body repair I choose to replace bad metal and minimize the use of Bondo type material. Your mileage may vary.
Below is a hood from a 1949 8N. This hood has multiple coats of paint, while ugly; they have protected it and minimized the rusting.
Disassemble the hood. I use paint stripper and strip the hood. Perform a close inspection and look for rust in the lower rib running along the length of the hood. They usually rust near the front and along the side near the rear cross support.
In this photo I will repair a hole drilled through the hood a long with some rust:
Cut out the damaged area using a cutoff tool:
Make a filler piece. I use an old Ferguson hood which has similar rib features. I spend time with the bench vise and a hammer shaping the piece to match the contour. A tight fit is best. You could also use an old fender/. The steel is about the same thickness.
Here is another repair to the other side. Cut out the old damage first and make pieces to weld back in:
Tack in the pieces:
Carefully tack the new pieces in keeping everything lined up:
Once everything is in place and lined up, weld it in. I work in small areas and alternate allowing the metal to cool to minimize distortion. I use an acetylene torch but a mig welder would be easier to use.
Check the repair and make sure it is not higher than the surrounding metal. I hammer the high spots down. High spots will be visible when painted.
Once the repair is in, sand blast the exterior of the hood and inspect for more damage. Sandblasting has a way of locating holes in the hood. I also mark dents on the inside before blasting as they can be hard to locate after the hood is blasted.
On small pinholes, I use a center punch and drive them in towards the middle. I then fill them with brass (brazing).
Once sandblasted you can use the filler of your choice and fill it in. Be careful to restore original lines etc. You can also work on hammering out those dents and using Bondo to you liking. Once I have my repairs filled to my liking, I prime the outside of the hood with red primer. With Bondo I use 80 grit sandpaper, followed by 150 grit, followed by 220 grit and then primer.
Just about ready to prime:
I am using automotive type primer with high solids for surface building. It has very quick dry time which allows you to sand and prime, sand and prime, sand and prime.
Next I use spot putty and fill in the small imperfections. I also hammer out the dents I missed the first time. (That’s why I did not prime the inside yet). Wet sand the entire primed area. Pay close attention to the repairs that you made. If they are not right, stop and fix them now.
Next sandblast the inside and prime the entire hood. This time I use gray primer. Now get comfy and start wet sanding with 400 grit and sand out all those imperfections. The more time you spend here the better the hood is going to look! The red primer will be an indicator of how deep you are getting. You can always sand away and re-prime if necessary.
Once you are happy with the hood you can get ready to paint. In this photo my hood is ready for finish color. It has been primed gray inside and out. I find it easiest to paint the hood hanging this way.
Now paint with your coating of choice following the mfg’s directions. Be sure to paint inside the hood around the cross braces and along the horizontal rib.
Finished hood, it’s getting late and I had to put the toys away in the shop. The 43 in the background will be painted all gray some day, it just came in one day for a water pump and while the hood was off I decided to, well you know how that story goes! Here are some other parts that I painted using the same process:
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