On my '53 F-100, the very bottom of the door skin (like all our trucks) is folded over to engage the inner door sheet metal and then permanently joined by spot welds. Over the years the weep holes at the bottom of my door must have clogged up, because I have small spots of through-rust at the bottom of the inner sheet metal. This rust does not present a big visual problem for me (the outer door skin didn't rust through). But the joint between the two panels has rust between them that runs the length of the door bottom and about three inches up each side. I have gently tapped along this joint and that has broken away some of this rust, but I'll never get it totally clean; it can't be gotten to without actually separating the two pieces, something I don't really want to do. I'd like to treat this area in a way that would give me some confidence that, as long as the weep holes work properly, I won't get blistering paint along the bottom of the inner door sheet metal. Short of limiting my driving to only dry days, what are my options? I have considered saturating the bottom of the door in rust converter and then priming the inside bottom of the door with POR or some similar product. Any ideas? I'm pretty sure that I can't be the only person here who has faced this.

 

Of course you already know the only way to be sure is to cut out the rust and put in new metal, but not every build warrants that type of repair. I have not tried it but I would think your idea of using a metal prep solution and por 15 would work fine. I would wire wheel the area to remove as much rust as possible and then go from there.

 

Hey John,
Our '50 has (2) bubbles in the paint on the lower driver's side door - Grrrr.... Take your time & prep the area as well as you can. It's easier to deal with it now than later on like us. Patience isn't my long suit.

Ben in Austin
1950 F1

 

Well, patch panels to replace the rust will run about $85 for the affected door. And, gobble up at least another weekend. Only the driver's side door needs attention, thank goodness. I know that if I take the shortcut and the paint blisters in a few years I'll regret not dealing with this properly. I guess it's time to place a parts order. Thanks for your advice.

 

Take the door off and lay it down to make it easier to work on.
Drill the spot welds with a spotweld cutter.
You can buy a tool to open the fold or make one out of an inexpensive pair of pliers (ask how if interested). Unfold the outer skin.
Decide how much of the inner frame needs replacement to get back to solid metal, cut away rusted area and cut patch panel to match.
Clean any surface rust from inner surface of outer skin (decide if any of the outer skin needs replacement, now's the time if it does. If all but the very bottom of the outer skin is solid you could take some 20ga cold rolled sheet to a sheet metal shop and have a suitable width strip sheared and bent to 90*. If you are not replacing more than a couple inches of the outside it doesn't need to be rolled into a compound curve, so you don't need a preformed repair panel.
Spray the inner surfaces of the outer skin and the inner frame with a good coat of weld thru primer. (available in rattle can from Eastwood or a body shop supply). Drill 1/4 - 5/16 holes in the outer skin flange with a step or "xmas tree" or unibit drill (never drill sheet metal with a standard twist drill, it will catch and tear out the hole and/or leave significant burrs) for plug welds to replace the spot welds if you replaced it.
You can also buy a crimping tool to bend the flange back or use a flat rectangular faced hammer and dolly. Bend it down in several progressive passes so you don't stretch and wrinkle the flange, especially if reusing the original opened outer skin.
Rosette or plug weld the outer skin flange to the inner frame.
After everything is cooled, wipe a fillet of #M or SEM paintable seam sealer over the edge of the outer skin and along the junction on the inside so water can no longer get between the panels. Be sure there are sufficient open weep holes along the door bottom.
Paint the inside of the door with a single part moisture cured urethane coating like POR 15.
Metal finish and fill the outside of the door as needed.
Rehang the door, prime and paint.