HMV Body Work Basics

By Kerry Bernstein

As caretakers of our respective country’s privately held historic military vehicle inventory, we are all familiar with the simplicity and function built into these capable vehicles. Those features are what set our HMVs apart from the high tech 21st century car in the showroom. One thing these steel soldiers have in common with the soccer-mom-mobile, however, is, actually, steel. And rust is an equal-opportunity employer. The slow burn of auto body cladding shows no mercy to the bravest of history’s military fleets. Auto makers went to galvanizing auto bodies to slow rust, but the best that most military services could do was retrofit their vehicles with work orders for spray-on coatings such as the old “Rusty Jones” treatments. It is inevitable that “Vermont Red” will appear sooner or later on your MV truck, and it’s important (and economical) to stay current on how to deal with it.

The biggest military vehicles, naval warships, have an effective defense against corrosion. Naval ships drag zinc “sacrifical anodes” closely behind them. Ionic currents between the anode (zinc) and the cathode (steel) through the electrolyte (salt water) liberate the zinc atoms (which have lower dissociation energy) before the steel atoms, mitigating corrosion damage. While in an auto dealership’s repair waiting room, I read some literature hawking “electronic” rust prevention, which claimed to reproduce this sacrificial anode response, but with an electronic pulse generator attached on opposite ends of the lucky automobile. The literature offered a patent number as proof the idea worked…..smelling snake oil, I looked up the patent, read the claims, and was immediately reminded of an infamous P.T. Barnum quote about suckers who will buy anything.

Military vehicles are both more prone to rust, and more easily repaired. More prone to rust mainly because the relatively spartan MV designs offers limited weather sealing and drainage; the vehicles naturally sit outside most of their lives in the rain and snow, where road or ocean salts accelerate the conversion of our load warriors into garden soil. Entropy ultimately wins. Our trucks also tend to be much easier to repair than civilian chariots because of the noticeable absence of anything remotely stylish or curved in the body – doors and fenders tend to be flat and orthogonal, body panels bolt together, and the steel tends to be thicker and easier to weld on.

As a matter of fact, as you become familiar with any given model of military vehicle, chances are you already know where to expect to find rust. On the deuce-and-a-half for instance, if you find rust anywhere on the truck, it’s likely to be at the bottom of the doors, or on the driver’s side front fender, the example for this article. It’s so common, that I sometimes wonder if they were designed with that intent.

Luckily, the techniques, tools, and materials used to repair military vehicle rust damage are not unique to OD-colored trucks, nor are the tools specific to the military. The materials you need to have on hand include:
- New sheet metal 14-16 ga.
- Polyester body filler (the ubiquitous “Bondo”)
- Metal cleaner / acid etch prep
- Metal primer paint
- Body Paint (code specific to your vehicle)
- Sandblast media (i.e. “Black Beauty” which has
another use we’ll cover)
- Sand paper

The tools that make this job half-way enjoyable include:
- MIG welder or oxyacetylene torch with welding tip
- A plasma cutter would be SWEET to have,
but a sawzall works too.
- Electric hand grinder
- Electric sander
- Sandblaster
(siphon type is inexpensive and does the job well)
- Tin snips
- Paint spray gun

Repairing even a major rust hole is easily accomplished in a weekend, if you’re lucky to be left alone that long. It can be done over a longer haul in smaller bites, as long as you stop at “safe points” which will not compromise all the work you’ve already done. Let’s take the job repairing a major blemish one step at a time.

1) Cut out the damaged area using a hand grinder, sawzall, or plasma cutter if you got one. Cut enough beyond the rust so that you’re sure to get back to good steel. Make the cut as square and dimensional as possible, and watch for additional welds to be removed. On the deuce fender, hidden tack welds from the fender panel to the underlying steel support rib have to be chiseled apart. Once you get your cutout off, you can sandblast, clean, and prime any underlying steel that also rusted which was previously inaccessible. Again in the deuce fender example, under the panel is a supporting structure steel rib which also rusts but is inaccessible. Take the chance to clean it up. Finally, with the cutout removed, grind off the paint in a ½” margin around the hole so you have something to weld to later. If its time to help your kids with homework, you can stop the work here for the evening.

2) Cut a steel patch from the sheet metal you bought so that it fits the hole you just cut. Cut it 1/16” to 1/32” smaller on each edge, so that the heat expansion during welding does not cause the steel patch to deform. Clean both sides of the steel with the metal cleaner / acid. This is a real good time to use those rubber gloves you have on your workbench. This phosphoric acid etch is a very important step in preventing premature rusting of your patch once it’s put back on. After 3 minutes rinse off the acid, dry the steel patch, and paint the back side with two coats of the metal primer. It won’t be accessible later.

3) OK, Sparky, finally time to weld. The name of the game here is MOVE QUICKLY! Our old warrior’s steel is not what it used to be, and your patch is also not that thick a steel. Move too slow and you’ll be knitting holes shut later on. If you have a MIG welder, use 0.024 wire at your lowest available voltage setting. For acetylene welders, try to get away with the lowest heat delivery possible, and don’t forget the borax!! The low tech alternative to welding is to flange around the opening you cut, and pop-rivet your patch to the flange. Then with a ball-peen hammer, ping the rivet down below surface level, so that it can be smoothed over with filler.

4) Pretty-up your patch. First grind flat all the welds, and while you’re at it, roughen-up any bare steel so that it will hold filler. Next, mix up about a golf-ball sized quantity at a time of your polyester filler and “spackle” in low spots on your patch. MV panels tend to be large and flat, so make sure you use a good “squeegee” to smooth out the filler so it looks good. When it hardens, sand it smooth and then again acid-clean any exposed steel. Wash the whole area to remove the acid and filler dust, quickly dry it (I used my wife’s hair dryer, but she doesn’t need to know that) and then prime with 2 coats of metal primer, overlapping onto the untouched area. Here’s another safe place to stop for the evening.

5) Finally, spray on multiple thin coats of your finish paint. The finish coat will have a different finish over primed metal than over sanded filler, so it may take a couple coats to regain the uniform appearance.

Needless to say, the above process can be abbreviated for lesser insults to your MV’s body. For smaller patches that have bubbled up paint but have not yet rusted through, it is sufficient to grind open or sandblast the area back to shiny steel, acid-clean the metal, and then pick up the above procedure at step 4. Once thoroughly cleaned, “bondo” filler can be spread across the top to eliminate pitting the rust caused. The military is famous for this quick fix; this will be evident when you take on repairs previously addressed by the military.

Fenders and steps on many M-series vehicle use a non-slip coating which can be a challenge to patch. An easy, inexpensive trick does a great job when replacing non-slip surfaces. After spraying or brushing on the first of the final finish coats, hand-sprinkle a thin layer of “Black Beauty” sandblast media onto the wet paint.

Black Beauty is a black, glass-like slag by-product which is crushed and screened to a fine uniform size. Pat the sand down into the paint, lightly air-blow off any excess that didn’t stick, and then slather more paint over the media-sanded panel after it dries as a second sealing coat. Do the whole panel so it looks uniform. It works great, looks like what the military originally did, and saved you the $55-a-gallon they’re getting lately for non-skid paint.