Welcome to the BugShop FAQ

Introduction

While this article could be thought of as "turn four" of the #4 resto, it will cover some things that go back to the early phases of a resto, namely "Metal Finishing" or "how to get from dents and rust to shiny paint". As I write this (on a United flight from Boston to Chicago) I think about how useful it would be to offer a summary of the steps involved in getting a panel done. Having spent much time in my friend Tom's shop and watched him use tools, techniques and materials, I feel that I have a pretty good handle on the high level steps involved in getting to that "#4" result.

So this article will deal primarily with metal prep and painting. Keep in mind that this is true top notch, done right, body restoration. As my own '57 has just made its return trip home from the body shop (just the bare body shell mind you) it does occur to me that subsequent articles dealing with interior and wiring installation will be warranted.
 

Metal Work: Done!

I covered much of panel replacement and welding techniques in the previous article, but lets make sure we make clear where we are now, before we start talking about painting. I'm sure I aggravated Tom a lot by tweaking, pulling, re-welding, drilling and straightening stuff on my car that was supposed to be "ready for paint". Additionally, my definition of "ready for paint" was not the same as his (see the roof work that needed to be done on Page 11 of the '57 resto series).

The difference between a good body man and your typical novice with a sander (and the half-gallon sized can of bondo) is how far the metal is worked before paint is even discussed. A good bodyman uses his hands probably more than his eyes when it comes to assessing the readiness of a metal panel for paint products. Many shallow dent and 'low spots" can only be felt, not seen in bare metal. This is especially true for large, fairly flat panels like doors and roofs. Use the open palm of your hand, with light pressure and close your eyes. Slide your hand slowly across the panel. Do this several times. If it doesn't feel perfectly smooth, it isn't going to look perfectly smooth when it is painted, guaranteed. It is easy for the novice to want to fill dimple dents of all sizes with a good coat of filler, but that is not the way the experts do it.

So how do you pull these dents out? Well in the "old days", a hole might have been drilled and a screw bit on a slide hammer might have been employed. If access to the back of the panel is available, the metal might be worked with a hammer and dolly, a slapping spoon or a fender pick. More recently, a device which welds small pins the the panel, and another tool that pulls the pins might be used (the pins are then cut and ground off).
 

Well, in Tom's shop, there is only one tool that is used for this task. It is called "The Eagle". It is basically a device that temporarily welds itself to the panel and allows the user to level out the area. A quick twist of the big D handle, and the pointed copper electrode breaks free. What the body shops like best about this device is the fact that it generates very little heat in the panel. So little that interior material and insulation touching the backside doesn't even get scorched. You can pass you hand over the panel as soon as you release the tool and it just feels nice and warm. At each point where the electrode pulls the panel, the metal is slightly "blued", and "pimple" can be felt. Once the panel is pulled out sufficiently, the Eagle performs another very cool trick. On the top of the big D handle is a another rounded copper electrode. This electrode is touched to the pimple top and the trigger is pulled. A current flows for a timed interval (adjustable on the tool's control box, about a second) and generates more heat at the pimple top which shrinks the metal back down flush. It is amazing to watch someone experienced with this tool use it. "Low spots", those long dent gouges (common in doors as the car swipes a fixed, pointed object) and good old deep dent nicks (species shoppingus cartus hitus) are no match for this tool.

The tool is really no more expensive than a good MIG or Arc welder ($400-$500), but might be difficult for the novice to justify purchasing. Consider grinding the metal bare in the problem areas and then taking the car to a shop with such a tool and have them pull it out for you. Doing this step right insures that a minimal amount of filler will be needed, and maximizes the strength of the panel. Obviously, we are beyond panel replacement and/or welding in patch panels here. Once the panel is pulled out to satisfy even the expert bodyman, you will still fell unevenness using the "palm" test. But less than 1/8" of filler will be needed to make the panel smooth!!
 

A couple other tips worth mentioning. Use a light source light parallel to the panel surface to visualize low and high spots. You need as much of a "point source" light as you can get. This is a light that emanates from a single point rather than a reflector or a coated bulb surface. Your standard 75 watt household light bulb will not work well for this as light radiates off the entire bulb surface as opposed to a single point. A flashlight isn't much better as light is cast off of the reflector primarily. What you want is a clear glass bulb with as small a filament (the thing that glows) as possible. I find 12 volt parking light bulbs pretty good for this. A tiny halogen "marker" light bulb used in newer cars is even better. Rig one up in a socket or solder leads to it. Now get the filament as close to the plane of the panel as possible. Turn off all other lights. On a door, hold it right at the edge of the door. Place a finger or a pencil near it and it should cast a shadow all the way across the panel if the bulb is positioned correctly. You get the idea. With light shining across the panel surface perfectly parallel to it, low spots will appear dark, high spots lighter. You might be amazed at what this reveals. Of course no body panel is perfectly flat, you will have to continuously move the light to "scan" the panel. For the roof, slide the bulb along a line down the center, starting from the back and working forward, keep your eyes at the panel level, or slightly above. If you are looking straight down on it, you will not see the differences in the light.

The other method is often used in body shops. It involves a "guide" coat of paint covered by a contrasting paint. For example, spray black, then cover it with white. Now sand the panel with a rubber block or "sled" sander lightly. The high spots will show the black underneath almost immediately. Make note of them. Keep sanding and the low spots will stay white.

I like the light bulb method better 'cause it doesn't involve as much work and you get to do stuff with wires and electricity.
 

Sand Sandblasted Bare Metal

When Tom told me that I had to sand the body before he did anything I said "Sand what!? It's bare metal!!!" But sandblasting leaves a surface a little too pitted for even high solids primers to deal with. If your metal has been sandblasted, sand it with 80 grit before doing any fillers or primer. It will smooth it out.
 

Filler (the "B" word)

Bondo, or plastic fillers in general, get a bad rap I think, for the same reason that guns do. It isn't what the stuff itself does, it is what people do with it. I remember an article by my favorite writer in Road and Track, Peter Egan, where he talked of buying a "salt car" (that would be a second, sacrificial "beater" that held no emotional value). He said "it is not uncommon to see a Cadillac with Bondo applied with a mason's trowel to the headlight nacelles.....". Fact is every body shop uses filler in almost every repair that they do, it is even used on some less than perfect replacement new panels. But it is how it is used that is different.

Tom uses a filler called "Rage" by Evercoat.  It comes in the big gallon can, smells and looks like Bondo, uses the cream hardener in the tube and is mixed on the scrap piece of cardboard with that yellow plastic spreader. He says it is better than Bondo because it sets up much faster, it can be sanded in about 20 minutes. But it is never applied in a thickness greater than 1/8", usually a sixteenth or less. What that means (refer to "Metal Work: Done!" above) is that your panels must be worked (or replaced) to within an eighth of an inch of original!

Filler (as I will refer to it from here forward) is always applied to bare metal and bare metal only.  It should be mixed with hardener until it is of uniform color throughout. It is then "skimmed" over the surface being careful to feather it to tissue paper's thickness at the edge of the applied area. Press reasonably hard and "wipe" it across the panel. There should be no bubbles or holes in the filler. Get those yellow plastic, flexible spreaders in various widths (auto body supply shop).

Almost always, filler should be sanded with a rubber block or narrow "sled" sander. For large areas, a "DA" air sander may be used initially (8" ones work best) with 80 grit paper. Only in small, irregularly shaped places might you hand sand (with fingers and folded piece of sandpaper) the filler. Use the "palm" method to assess smoothness (remove rings if you wear them). Once the surface is uniform, sand again with 120 grit. Anal? Get that light out and do the shine test again.
 

Glazing Compound

The purpose of glazing compound it to provide a glass like surface over the filler. No matter how fine a paper is used to sand filler, it will always have microscopic "pits" that primer alone is not designed to fill. Glazing compound is applied over filler to smooth out these pits and provide a super smooth surface for the primer. The glazing compound is sanded to 220 grit.
 

About Paint

Before we go beyond the glazing step, lets take a minute talk about auto paint in general. If you are like me, you might ask "Why is it so special? Why is it so damn expensive? Would a $3 can of Krylon do just as well?" First of all, don't focus on just the paint. Think of a paint system Color coats of Dupont paints weren't designed to go over coats of PPG primer. And a Martin Senouir metallic wasn't designed to be sprayed over AutoZone brand auto primer. You must always spray paint on something that it was designed to be applied to, else the results may very well be less than acceptable. Well of course you have to start somewhere.

Ideally, you start with bare metal. Either sanded, ground or sandblasted bare. For this you should use a etching primer. An etching primer contains acids that slightly eat into the metal surface and insure good adhesion to the metal. Over that, you spray a sandable primer from the same manufacturer. This allows you to sand the primer to a mirror smooth finish with 600 grit sand paper. Sandable primer is sometimes called "HS" or high solids primer. This means that it builds up a thickness that can then be sanded down slightly to perfect the finish. Etching primer is not an HS primer. There is also something called "spray bondo" (ooops, I said the "B" word) which is just what it sounds. A super high build filler that can be sprayed and worked down. Lastly, there is "vario" primer which is actually an etching primer and is sandable.

Now we haven't even made it to colors yet. There are single stage, two stage paints. In both solids and metallics. Then there are metallic flakes (a more "sparkly" metallic, hard to shoot because the flakes have to all "lay" the same way). Urethane paints have all but replaced the enamel and lacquer paints used in the past (check out Spies-Hecker's website for more information on paints. My '57 was painted with S-H paint) Enamel paints can't match the gloss and durability of urethanes and lacquers have been largely outlawed due to high VOC (volatile organic compounds) production. Some paints have isocyanates (very harmful carcinogens, you need a fresh air breathing apparatus to spray them, not just a respirator) some without. There are catalyzed paints and some with hardening compounds and some with "flex" (for plastic bumper covers and the like).

I'm not an expert here, I'm not even going to try to sort it all out or make recommendations. I'll say just two things, if you are interested in learning more go to you favorite bookstore or library and find some books on autobody paints, they are out there. And most important, use a matched paint system.

So you might be wondering, "Do you mean I have to start with bare metal??". No. Most paint systems have a primer/sealer that can be applied over some other paints. But you have to know what that paint is. Most good paint systems have a primer-sealer which is used as a starting point, that is is it is designed to adhere to a variety of different coverings and insure that none of the original color bleeds through. Do you know what is on your car? Unless you are sure, it is best to strip it down to metal. Remember it is not just the risk of adhesion between your primer sealer and the top coat of what is on your car, but the coats of primer and paint that might be under that....and under that...and under that.....
 

The Basic Steps

 Ok, I'll take a stab at the basic "soup to nuts" steps involved in at least what I did with my '57 in terms of body work

• Heavy metal work- This is the panel replacement, patching or pounding. The real replacement or re-working of damaged, rusted or nonexistent panels. See pages Two and Three for methods to accomplish this.

 
• Final metal prep- This would be maybe some minor metal pulling, bending tweaking and then sanding and/or sandblasting. This is when you must "fit everything up". Bolt everything back together and make sure you are happy with gaps, how doors close, etc.

 
• Filler stage- On bare metal only. This is where low spots are filled and then sanded. I really believe that in all of this, this requires the most skill/experience. I have never been able to do this worth a damn. This stage also includes glazing compound.

 
• Primers- Yes, primerS, plural. First of all, any bare metal not already covered with filler/glazing compound, must be sprayed with etching primer (just spray around the filler'ed areas, a little overspray on the filler won't hurt). Then the whole area is sprayed with "HS" or high solids primer.

 
• Sanding- ...and lots of it. This is what separates the decent from the great paint jobs. Hand sanded, wet. Should be glass smooth.

 
• Primer again- Your sanding stage will have invariably sanded "through" the HS layer, you want a uniform layer to spray the color coat on. Spray HS again, sand again lightly.

 
• Final paint prep- Blow it off with air, mask off. Then wipe down with a surface prep. See Page 12 for tips on how my '57 was prepped before and in the paint booth.

I'm sure I will be adding a bit more to this article in the future and will actually add subsequent pages to cover the interior install and other stuff.  For more on painting, check out the "DIY Paint Job" article....
 

Copyright© 1999; John S. Henry