Patching Fender Rot

It seems like all we talk about when working on Project Pile House is the rust and body damage it has.. but again today we're covering the repair of more rust that's on the truck. This time it's on the sides of the fenders where the cab mounts attach to the fenders. Originally they sandwiched multiple pieces of metal together and riveted the mount through them for additional support on the fenders. This spot is very prone to rusting on these trucks and should definitely be addressed. On Pile House both fenders were rusted badly and the rot was covered with a heavy coating of body filler to hide the damage. In my effort to clean up the exterior of the truck, I wanted to get rid of the rust and rivet heads when making the repair. In the end, I modified the cab-to-fender mounts so I could spot weld them to the fenders after positioning the fenders to get an even gap where the doors and fenders met. This was pretty boring, time consuming, and hard to photograph.. so I'll save you the winded post about that process in this update, and focus on repairing the rust and smoothing the fenders.

The first thing I do when making a repair like this is to use painters tape to mark out the area I want to remove and repair. I usually tape off just a little further out than the rusted area so I can be sure that I'm into good metal when welding the patch panel in place. It's really difficult to weld thin, heavily pitted metal, so it's best to remove a little more so you can get a clean area to work with.

The other nice thing about the painters tape is that it gives a nice straight line to follow as you cut out the area you're repairing. I chose a 4 1/2" Electric Angle Grinder with a cutting disc to make the cuts. I just put the edge of the cutting disc against the inside edge of the tape and followed that as I made the cut.

Once I had the cancerous areas removed, I cleaned the area surrounding the hole with a flap disc. With the area prepped, I could then make a pattern of the patch panel I needed. I chose to use a manila folder as my pattern, although you can use thin cardboard, chipboard, construction paper, or any other thick paper product. Chipboard is often the best to use as it behaves the most like sheet metal, but construction paper or a manilla folder will work ok as well (and is easier to find). Once I traced and cut out the patterns for each patch panel, I transferred the pattern to the metal and cut the rough shape from 18 gauge steel with the Electric Metal Shears. Once I had the rough shape cut, I could then trim the piece to shape with a set of Eastwood Aviation Metal Snips. After I had the patch panel close to the size I needed, I used the curvature of the fender to give the patch panel a slight contour to match the fender. Alternatively you could use a pipe form, a Slip Roll, or even an English Wheel to shape the panel. But in this case, the curve needed was so slight, using some muscle and the fender as a form, gave me the shape I needed.

On this repair, I chose to use a set of Intergrip Panel Clamps to gap and hold the patch panel in place. Then the Eastwood MIG 175 to weld it all together. The key with using the intergrips is to use the aviation snips to carefully cut the panel just a bit smaller than the opening so that the mounting plate for the intergrips can slide between the old and new metal. This allows your welds to bridge and fill the gap.

Once the new metal is clamped in place with the Intergrips I used a flathead screwdriver to get the panel centered in the opening and began laying a few quick tack welds to attach the new metal in place. From here I like to move my intergrips around and tighten them in place after each tack weld to get the patch panel flush with the surrounding metal. On a curved panel like this it's important to make sure the curve of the seam matches. Once the patch panel is tack welded in place and lined up correctly I removed the Intergrips.

Now that the patch panel is tack welded in place, I began stitch welding the joint closed. I like to jump around the panel making quick, hot welds. On a patch this small I had to be careful not to introduce too much heat into the panel and warp the metal. I like to keep a blow nozzle from the compressor handy to hit the welds and metal with cool, compressed air every few welds. I make sure the panel is warm or even cool to the touch before I continue laying stitch welds. If the metal is too hot to touch with your bare hands, you shouldn't introduce anymore heat into the panel until it cools. After some time I ended up with fully stitch welded patches that didn't have any major warpage.

After I've made sure the panel is fully welded, I used the flap disc on the angle grinder to grind the proud welds down. The key is to grind across the welds so they're flush with the surrounding metal. If ground too much, the weld joint will be thin and weak. With this repair method you should be able to grind the welds pretty much flush with the surrounding metal. I then used the Eastwood Pro Hammer and Dolly Kit to bump up any low spots from welding. For now I sealed the repair area with Eastwood Self Etching Primer until I'm ready to lay body filler, primer, and top coat.

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