CLICK TO PRINT – QUESTION SHEET

Intro

I will walk you through the prep work and completion of a basic paint job. All of this is just skill development, something you have to spend time developing.

Note: I hate bodywork. I’m not good at it, and I don’t like doing it because I’m not good at it.  But, my skills have slowly been developing…

We will look at the following stages of painting a vehicle:

• • Stripping
  • Rust Repair
  • Dent Repair
  • Preparation
  • Priming
  • Painting
  • Reassembly

Image from Kocher’s Custom Paint

Stripping

The difference in any job is attention to detail. Attention to detail separates the good paint jobs from the awesome ones. You can see the crappy paint jobs in the back rows of sleazy car dealerships: overspray on the fenders, window trim, tires, tail lights. Nasty. To pull this off, you need to pull all this stuff off.

Removing the lights and trim are easy – they either attach using fasteners, or are clipped or glued into place.

Most trim and emblems today are often held on with double-sided tape – be prepared to have to clean off some adhesive residue, and to re-tape them in place.

Most people do not remove all the windows and window trim, however you can often stuff a piece of string under the window rubber to raise it off the metal so you can prep/paint underneath it. Inadequate prep around edges is the number one cause of paint peeling up and/or chipping off.

Doing a full body-colour change requires the most prep, as the underside of the hood and trunk and the door jambs will still be the original colour, unless you really go to town and prep and paint those too.

Try to find a secure place to store the parts you remove. Putting them inside the car is common, but be careful not to damage the interior panels in the process. It is also a good idea to Tag & Bag the parts so you can remember what they are, where they go, etc.. Ziploc bags are awesome for this sort of stuff.

Image from Rich’s Autobody

Image from www.v6stang.com

Rust Repair

Once you have the car all disassembled, you need to take a good look at where the problem areas are.

Every car has their particular areas of severe rust. Study those areas from both the outside and the INSIDE of the panel. Just because you cannot see it through the paint does not mean it is not there. Any perforation of the metal on the back side, under the paint, is an invitation for rust to start. And it will.

Here are some of the most common rust areas, and are also good places to inspect vehicles you wish to buy:

• • Rocker Panels
  • Fender Edges (Especially the rears on Hondas)
  • Bottom of the A-pillar, behind the fender
  • Floors, especially under the feet, and near the corners
  • Rear window opening
  • Windshield base
  • Trunk Floor
  • Cab mounts on pickups

If you can stick a screwdriver through it, it’s terminal and needs to be fixed.

Rust repair is best done like this:

• • Strip or Blast to bare metal. You need to know the extent of the rust. I prefer blasting, as it gets the rust out of the very pores of the metal.
  • Cut out the rusted area. Cut until you come to solid steel. On some cars, you are going to have to make a judgement call: I have worked on cars so rusty I had to stop cutting or I would have nothing left to attach to. A plasma cutter is the cat’s meow for sure. A body saw for small stuff, or a Sawzall is for biug stuff is awesome. Tin snips and/or jig saws are great for the little bits. I like to use an air-powered cut-off saw (also called a Zip Disc) – I find them to be very versatile in body work.
  • Fabricate a patch panel. Sometimes you get lucky and aftermarket patch panels are available. Use them if at all possible. Keep in mind, though, that aftermarket panels rarely (if ever) fit properly. Expect to spend some time to make them fit.

I bought an aftermarket replacement panel for the box side of my truck. While it looked correct, it was not curved correctly, the fender arch was not curved correctly, and the detail of the fender edge itself was absent. I was very unimpressed.

I recommend not using the entire panel if you don’t have to. Only cut out the rust, and trim down the replacement panel to be only as big as you need. This requires less work, as well as less chance of really screwing it up big.

• • Attach the patch panel. There are a variety of ways to do this. Whatever method you choose, BOTH SIDES of the panel must be SEALED or moisture will start rusting it out again within a year.
    • Structural Adhesive – A more modern approach. This works well as there is little distortion from welding heat or improper riveting technique. Many cars today are glued together – the Corvette, the Lotus Elise. If it works for them, it should work for us too.
      • Advantage: This does not put heat into the panel, so it will not warp the metal like welding does.
    • Rivets – Easy to do, no special tools. Get good rivets – don’t use hardware store rivets, they are made out of butter. Keep in mind that most common rivets are hollow, which will allow moisture to pass through. I dip the end of the rivets in structural adhesive before using them. The adhesive helps seal the rivet, as well as seals the hole. It is best to have all the holes drilled first, but that makes holding the panel in place difficult. Clecos are used to secure everything together temporarily while you finish drilling. Start riveting in the center of a patch panel side, and work your way to the corner. As the panel is attached, the corner gives somewhere for the metal to go. Starting in a corner results in “bows” in the middle of the panel.
      • Disadvantage: you’ve perforated the metal, so water could get in.
    • Lap Welding – A flange is formed around the perimeter of the hole, providing a recessed fit for the rust panel to sit and be welded. This makes it easy to weld, as the doubled-up metal is thicker and less likely to burn through.
      • Disadvantage: the “overlap” can trap moisture and rust worse
    • Butt Welding – The patch panel is fit with such close tolerance that the patch panel edge is welded directly to the original panel edge, edge-to-edge. Done correctly, light grinding and very little filler is needed to bring the panel to perfection. The repair can also be invisible from the back side, ideal for restorations and show cars.
  • Neutralize existing rust. Rust never sleeps. Rust is a cancer. You don’t find rust, it finds you.  Lucky for us, one of the things we can do is chemically neutralize any rust that may be lurking in the exposed steel around our fresh repair. There are a number of off-the-shelf chemicals we can use. The main ingredient is Phosphoric Acid, which converts the brown Iron Oxide (rust) into a black Iron Phosphate coating that can be scrubbed off. The metal is now neutralized from rust, and can be Bondo’d, primered and painted. Do this over your lawn – the grass loves it. By the way – Phosphoric Acid is a main ingredient in many soft drink colas. Yum!I like to use this stuff on any bare metal prior to finishing. “Rust Mort” is one brand.
  • HOKEY METHODS
    • There are other ways to repair rust, though anything other than a patch panel is hokey. Here are some:
      • Expanding Foam – “Great Stuff” from Home Depot, stuffed into a gaping rust hole, and then shaped to fit once the foam cures. This will show rust in less than a year, and the result will usually be worse since the foam will hold in more moisture. Dude. Just say no. Yes, I’ve done it.
      • Kitty Hair – This is a plastic filler which uses either short strand or long strand fiberglass mixed in to give strength. Some people mix up Rutland size quantities of the stuff, and shove it into the gaping rust hole. This adds a lot of weight, and while the Kitty Hair won’t rust, the surrounding metal likely will. Then the Kitty Hair plug will fall out. Nasty. I’ve done that too.
      • Fiberglass – Using fiberglass cloth or mat to cover gaping rust holes. This is really messy, and still requires a lot of finish work to make it look right. The same perpetual rust problem as the Kitty Hair – I’ve seen perfect fenders for a couple inches, and then rust showing through where the fiberglass patch stopped. It has its place, especially for complex shapes that are difficult to fabricate in metal. I’ve also done that.

Image from Silver Star Restorations

Repairing a rusty door

Me, repairing fiberglass

Once all the rust has been repaired, I recommend sealing everything in Epoxy Primer. This is a very durable coating that seals oxygen from the metal (preventing oxidization – rust!). If you life in a humid climate, I’d probably epoxy prime the whole thing right after blasting, and the spot-touch the areas I metalwork as I go. Freshly blasted ,metal can be rusting before you finish spraying.

Rusty bubbles

Rust perforated the inner fender, continued rotting from the inside

Outer rust removed, inner rust removed and patched

Patch panel tacked for butt-welding

Finish welding

Welds ground smooth

Ready for filler

Me, repairing rust on my ’61 Apache

(image: Imperial Club)

(image: Autobody Tool Mart)

Dent Repair

You need to visualize the impact, and then through force reverse the collision. When a car drives a front corner into an object, as the bumper and fender move backward, the fender will bow outward just ahead of the front wheel (the wheel arch is a weak point of the fender). You cannot merely try to hammer the bowed part of the fender back in, as the fender Location is shorter and there is nowhere for ALL the fender to go. You need to pull the front fender mounts forward again, to where they are supposed to be, before you can begin working on the damage.

Imagine lightly denting the side of a pop can. If you go inside the can and try to pop the dent out, you will still have damage visible because the sides of the can were creased during the impact. You need to apply slight pressure on the inside (to replicate the initial force), but you also need to apply force to the creases outside on either side of the dent.

Doing this, you can actually see the dent slowly disappear. The trick, then, is to find ways to apply these reversing forces to remove the dent (you can’t always get to the backside)

• • Hammer & Dolly – Use for small dents. Hammering is ALWAYS done with a dolly. Hammering On-Dolly is used to remove dents, while hammering Off-Dolly is used to remove multiple dents (such as a wave or a wrinkle) at the same time.
  • Shrinking – Collisions stretch the metal, and hammering stretches the metal. To do the best repair, the metal must be shrunk. This involves applying a bit of heat, and then cooling the panel down. When metal is heated, it expands, and when it is cooled it contracts or shrinks – but it shrinks more than it expanded. By applying heat and cooling, some dents can be minimized significantly. Paintless Dent Repair is sometimes done by using Dry Ice to cool the room-temperature metal enough to cause it to “shrink” back to its original shape, without having to resort to less gentle methods.
  • Slide Hammer – Sometimes a bit more brute force is required. Holes can be drilled into parts of the dent and a slide hammer screwed into each hole and the dent gently persuaded back to something more manageable. The holes must be welded closed or moisture will get in through the back side and ruin all your hard work. Alternately, metal pins are spot-welded to the fender, or plastic tabs can be hot-glued on, removing the
    requirement to puncture the metal (try to avoid puncturing the metal if at all possible).
  • Port-A-Power – You’ve done a number on your car, and lack the upper-body strength to slide-hammer it back into place. This is a portable hydraulic ram that uses a variety of attachments to help push or pull portions of the bodywork to where it needs to be. This is to repair much more “structural” damage than a wee fender-bender.
  • Frame Straightening – This is where you really have to want your car. The majority of the vehicle is stripped off, the chassis is bolted to a huge steel table, and more hydraulic craziness is used to pull dramatically messed up vehicles back into submission. Most cars today are written off if they need this much work.

I have a friend with a very rare (one of two in existence, if I remember correctly) 1LE Pontiac Firebird R7U that he races regularly (1LE is a factory-built race car, R7U was specifically built by GM for the Player’s Trans Am series). At one race, he put it into a concrete wall. While any normal person would have thrown the car away, because of the value of THIS car, it was completely disassembled, a new front cut acquired, painstakingly welded in and completely straightened. Any evidence of the repair is invisible, and the car looks as good as it did before.

Update: A few years later he went off at Knox Mountain Hillclimb, wrecking it even worse.  The car is currently being rebuilt again.

Only the finest of craftsmen can completely remove a dent perfectly using hammers, dollies, and torches alone. For the rest of us mortal folk, we need filler.

Hammer Dolly Work

Plastic Body Filler (Bondo is a brand of plastic filler, not a product, though we often refer to any type of filler as Bondo) is a polyester resin product that is mixed with a hardener. When properly mixed, a chemical reaction begins which allows the filler to harden, usually within about 15 minutes.

The surface needs to be prepped for the filler to stick. I like to use 36-grit sandpaper on an orbital sander. Rough the surface up really well. You should try to get all the paint off – get right down to bare metal. It is currently good practice to lay down some etching or epoxy primer over bare metal, and then add your filler on top of that.

Filler must be mixed on a surface of some kind. I use a plastic mixing board, though cardboard or glass also work well. I have taken to mixing filler on a pad of paper – when I’m done, I just peel off that sheet of paper and throw it away.

You want to put a blob of the filler in the center of the mixing board, then run a bead across the blob. This is usually the right proportion. Don’t mix too much at once – you can’t deal with it fast enough. Use spatula-like spreaders to push the filler into the metal, and shape it quickly to approximately the right shape you need the panel to be. Be quick about it, as it sets up pretty fast.

As the filler is curing, it will go through a “rubbery” stage where it feels slightly sticky, but where it’s definitely firming up. NOW is when you want to shape the filler as best you can. A “cheese-grater” type file is often recommended, however I usually just use some aggressive sandpaper to knock it down to the shape I want. Be quick about it. Once it’s cured, you’re not going to enjoy shaping it as much.

The better you get at filler, the less prep work you have to do before paint. Any small defects can be filled with Glazing Putty – another polyester filler that comes in a tube. Smear it into defects with your finger. it is Lacquer based, and cures very quickly and sands very nicely.

Incidentally, I find it helpful to really scour the car for dents and defects and place a piece of tape over the defect so you can easily find them. It’s really disheartening to lay down fresh paint only to find a dent you forgot about and didn’t take care of. Shiny paint shows ALL your mistakes.

Get in the habit of letting your fingers feel the surface – they do a better job at finding defects or perfection than your eyes do – especially if it is all sanded, dull, primered, and dusty.

Heel (left), Toe (center) and General-Purpose Dollies (Rod&Custom Magazine)

Hold the hammer like this (though I tend to use my pointy finger along the handle) (Rod&Custom Magazine)

Always hammer with a dolly (Rod&Custom Magazine)

Shrinking (Rod&Custom Magazine)

Port-A-Power

Frame Straightening

Dented Fender (Mopar Muscle Magazine)

Removing all the Paint (Mopar Muscle Magazine)

Slide Hammering the dent out (Mopar Muscle Magazine)

Body Filler

Body Filler (Mopar Muscle Magazine)

Sanding – Always use a sanding block (Mopar Muscle Magazine)

Primer (Mopar Muscle Magazine)

Guide Coat – A light dusting of a darker paint is sanded off to help find any low spots (Mopar Muscle Magazine)

WAY TOO MUCH! (Thick filler cracks and falls out!)

Preparation

• • Mask – You attention-to-detail folks will love this part. You need to accurately and carefully mask off anything not to be painted. If you stripped the car down far enough, this should be easy. Follow the window rubbers as closely as possible – sloppiness will look like poo when you’re done. I have never seen a re-paint where I could not find overspray due to poor masking.
  • Clean – The entire vehicle must be washed down in a Wax & Grease remover. Use paper towels and surgical gloves. Use one paper towel to wipe down about a four square foot area with Wax & Grease Remover, and a CLEAN paper towel to wipe it off. Throw them away, and do the same again with the next area. Clean the vehicle thoroughly. You may not, at any time, touch the body with your bare fingers.
  • Sand – Sand the entire surface of the vehicle using around 600-grit sandpaper or finer. I often use a 3M green scrubbie for paint prep. You need to completely dull the finish. There must not be any gloss left in the paint at all. Pay particular attention to corners, ends of panels, and where the paint meets windows. Any really bad spots may require you to go down to 300 to get them out, but work back up to 600 or better.

Primer

• • Your first primer needs to be Direct To Metal (DTM). Many normal primers do not adhere properly to bare metal, or are porous and let moisture in to the base metal. I like to use an Epoxy Primer here. Epoxy Primer uses a catalyst to make it super hard (the fumes are toxic). You can do all your body filler right on top of the Epoxy Primer, and I like to spray another layer of Epoxy Primer on top of that.
  • Second coat of primer I like to use a high-build primer to deal with the last wee defects in the surface. This can be polyester-based (mixed around 1:1 with lacquer thinner), or a 2K product with a hardened (mixed 50:1 by weight.  Oh, and work FAST, it cures in the gun!). It is sprayed through a fairly large tip (2.0+) so you can lay down a lot of it. The “high-build” nature means that it goes on rather thick, so you can use it to fill in more imperfections.

You need to establish a good spray technique. Most of the students I observe using spray bombs must never have read the directions on the can, and do a terrible job of spraying.

The spray gun MUST stay a consistent 6-8″ away from the panel you are spraying. You need to keep the gun 90° to the panel as well.

The gun also has two parts to the trigger – just air, and then air/paint. You need to start moving the gun, and then pull the trigger, releasing the trigger before you stop moving the gun. This takes some time to perfect. Each path of the gun needs to overlap the previous path, and you should always spray wet paint on wet paint (wet paint overlapping dry paint will leave a noticeable mark when done).

You can use either a traditional low-volume spray gun (lots of overspray), or (better) a High Volume Low Pressure (HVLP) gun (requires a good compressor).

If you are spraying a habitually rusty car like a Honda or anything British, I recommend an Epoxy Primer. A self-etching primer such as Zinc-Chromate was the “go-to” before epoxy and is still pretty good. An Epoxy primer is super durable and water-proof. Most normal primers are NOT water-proof – they are porous. Let the primer cure for a few weeks before final sanding (2K at least 3 days) – the primer “shrinks” over time, and will continue to shrink into your sanding marks, making them visible after you’ve finished painting. This would then require more sanding, and possibly more primer.

• • Clean – Yup. Do it again.
  • Paint – You have a few more choices now.
    • Acrylic Lacquer – The easiest to spray, dries fast, and can be buffed to a high shine. Old fashioned, smelly, and really really not very durable. Lacquer has been outlawed as an automotive paint in many areas.
    • Acrylic Enamel – One-part enamels are the cheapest paints, not terribly durable, and the overspray is often hard to remove. It also takes a long time to cure. Two-part enamels add a hardener to speed up the curing process and improve durability. Acrylic Enamel dries to a shine – a clear coat is not required.
    • Urethane Enamel – Exceptionally durable. Polyurethane Enamel contains Isocyanites that are dreadfully toxic. Urethanes dry flat, and use a clear coat to give kit some gloss. A separate air source for you to breathe from is a good idea. This is my favourite paint.
    • Waterbourne Paints – The latest type of paint used. Quite expensive, but soon will be the only type of paint allowed due to environmental concerns.
  • The paint needs to be run through a strainer, and mixed according to the manufacturers instructions. A paint measuring stick is super handy to have, and makes the mixing part easy – it works for any volume of paint. Your technique really needs to be solid for painting. Especially your gun movement. Especially if you’re spraying metallics – they are not very forgiving.
  • Don’t lay all the paint down right away. Lay down a quick, light “tack coat” and let it set up for about 15 minutes. Start by spraying all edges (such as doors, hood, wheel arches, etc), as the paint doesn’t always like to fall on an edge easily.
  • Once the tack coat has set up, you can begin spraying. Again, start with the edges first.
    • With the gun properly set up, and the correct distance from the panel (about a hand-span off the metal) you want to balance your travel speed such that you can lay down a wet enough layer that it dries glossy but doesn’t run).
  • Then do the roof.
  • Start with a path through the middle of the roof, from front to back, and then overlap paths until you get to the edge. Then quickly go to the other side and do the same – you want to be spraying on paint that is still wet.
  • Then quickly start working your way around the car. Plan how you are going to do this, always laying fresh paint onto wet paint – don’t let it dry. All this has to be done fairly quickly as the paint will be dry to the touch within the hour.
  • Be mindful of brushing the wet paint with your body, bumping the air hose (I drape the hose over my shoulder so it can’t hit the paint), drips (a cut sweat sock around the paint can on the gun is a good idea), and runs (from laying it on too thick, my specialty).
  • If you are spraying metallics, I like to put a couple big ball bearings in the bottom of the paint can so I can swish them around to keep the metallic suspended in the paint.

I guess, alternatively, you can use a roller and roll the paint on.  $50 Paint Job. I’ve done that.

Masking (image: John Greenage)

(image: derek.com.au)

Primer (image: www.tonybmw.co.uk)

Paint (www.ppg.com)

Spraying Paint (image: John Greenage)

Basic traditional spray gun

HVLP gun with strainer and stand

Improper and proper techniques

Reassembly

Now is a good time to beautify any of the parts you took off the car – re-chrome the trim, powder-coat, accent colours, whatever.It is not recommended to wash or wax the car for about three or four months after painting. Any bird poop should be wiped up immediately, and gently. Rain should be wiped up gently as well, so as not to leave water spots.

A racing friend of mine had just had his Mustang painted, and he had a race a couple of weeks after it was done. He put magnetic numbers on the doors for the race, and at the end of the day the numbers stuck to the doors had damaged the paint, requiring a re-spray.

On the cars I have sprayed, I have not had that problem. I do not know what kind of paint he had sprayed on his Mustang.

DeTomaso Pantera