Projects & Repairs --> Automotive Finish --> Spray Painting

Painting A Car

The Basics Of Automotive Spray Painting

Painting Bare Metal After Sandblasting

 

In This Article:

A car hood is prepped for painting. Primer is applied and allowed to dry. Paint is sprayed in a pattern of carefully overlapping swaths and allowed to dry.

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Skill Level: 3-5 (Intermediate to Professional)

 

By Bruce W. Maki, Editor

Start:

As part of our 1957 Willy's Jeep restoration project we painted some parts while they were removed from the vehicle, such as the hood and front clip. Earlier these parts were sent to another shop for sandblasting.

The painting was done by Bob Mapes, owner of R-Tech Auto Body in Traverse City, Michigan.

Warning: Spray painting can be dangerous, hazardous to your health, and cause serious property damage. The painting shown in this article was done by a licensed professional in a paint booth with a fire suppression system.

This article should not be viewed as "instructions" or "advice". This article is for entertainment purposes only. Any person who plans on doing their own spray painting should read the additional warnings at the end of this article.

 

After sandblasting, the Jeep hood had a satin-silver appearance.

Car parts after sandblasting.

 

Metal prep with phosphoric acid.

Bob wiped down the surface with an ordinary metal preparation product, which can be found at an automotive paint supplier.

I understand that many metal prep products are based on phosphoric acid.

 

Cleanliness Is Critical:

Before painting a car, Bob ALWAYS wipes the surface with a lint-free towel and wax and grease remover, which is sold in auto body supply shops.

This is very important! Any oily substance can prevent proper paint adhesion, or bleed through the paint and be visible after all the work is done.

Cleaning metal with wax and grease remover.

 

Applying Primer To Bare Metal:

Applying primer to bare metal car parts. Bob mixed some Matrix MP480 Epoxy Primer and began painting the hood. First he primed around the edges, then he sprayed from side-to-side while working towards the middle of the hood.

 

Once Bob reached the middle, he quickly walked around and resumed painting, working toward the edge. Matrix epoxy primer.

After Bob was done applying the primer, he let it dry for about 20 minutes. This primer did not require sanding before the color coat was applied. Note that some types of automotive primers must be sanded before the color coat is applied. We strongly recommend following the paint manufacturers instructions.

 

Applying The Color Coat:

For the color coat, Bob used Matrix System's Single Stage Red #73218. (The single stage paint does not require a clearcoat, although clearcoat may be applied over it.)

First step: Painting around the edges of the part. Bob started painting by spraying around the edges of the hood.

 

Then Bob began making side-to-side sweeping passes with the spray gun, holding the spray tip about 8 to 12 inches from the surface and keeping the gun perpendicular to the surface being painted.  Apply paint in swaths from edge, working inwards.

Note how Bob holds the air hose in his other hand, rather than just letting the hose flop around. From my experience, it just seems more natural to hold the hose with the other hand... it keeps the hose away from the car, and it feels more balanced.

Overlap each pass by about 50% when spraypainting. On the second pass, Bob overlapped the first pass by about 50%.

This "50% overlap" concept is crucial to getting good results.

 

Once Bob had sprayed the hood half-way, he quickly walked around and began painting from the other side.

Note the angle of the spray gun. When spraying a flat surface, the gun needs to be tilted forward so it's perpendicular to the surface being painted.

Spray painting a car with parts removed.

 

The spray gun must be kept perpendicular to the surface being painted. When Bob reached the bend in the hood, he tilted the spray gun so it was closer to being vertical.

This change in angle may seem obvious, but from my own experience as a novice painter it's easy to forget to turn the gun upwards as you progress around a bend in the contour of the car.

While moving the spray gun from side-to-side, I've found a tendency to let the gun rotate as my arm moves. Whenever I do any spray finishing, I need to remind myself to keep the gun straight by flexing my wrist as I move my arm sideways.

As Bob reached the edge, he tilted the spray gun completely vertical and finished the last few swaths. Automotive spraypainting technique.
Almost done painting...

Applying the entire color coat to this hood took less than a minute.

After Bob painted some other parts, he spent a few minutes cleaning out the spray gun with lacquer thinner.

 

Quick Summary - Cleaning A Spray Gun:
  • Empty the unused paint from the cup.
  • Pour a few ounces of solvent (typically lacquer thinner) into the paint cup, swish around, and spray into a small container. Repeat.
  • Dismantle the spray gun by removing the air cap and orifice. Wash in a dishpan with solvent specified by paint manufacturer. Pour solvent into paint cup and let it drain into dishpan.
  • Use an air nozzle to blow the solvent from the spray gun body and parts. When dry, re-assemble gun.
  • Dispose of used solvent properly.

After applying the color coat to the hood and front clip, Bob let the paint dry in his paint booth for about 20 minutes. Of course, this is a professional paint booth which has a built-in furnace so the air can be heated to speed up the drying process. Bob says he usually heats the booth to about 105 degrees Fahrenheit.

While this red paint did not require a clear coat, Bob still applied it anyway. Applying clearcoat is tricky because it takes MUCH longer to dry, so it's easy to have problems with runs, drips and sags. The key is to apply a thin coat, let it dry for ten minutes or so, then apply a second and third coat (with ten minute drying time between coats).

Painting A Repaired Patch Vs.
Painting Bare Metal:

This article describes the methods used to repaint a car when all the old paint is removed down to bare metal. Note that painting a small patch on a car body can be different.

When applying primer, a special product called epoxy fill primer is used to obtain the proper paint thickness so the repair will blend in with the surrounding area. The primer is applied so it overlaps the original paint about 3 to 4 inches. The primer is "block-sanded" with 320 grit sandpaper and a rubber-backed sandpaper holder.

For most do-it-yourselfers, it's advisable to sand, mask, and repaint the entire body panel, because blending new paint into existing paint is very tricky and requires special techniques.

After repainting an entire body panel, clearcoat can be applied to the same panel.

 

Warnings About Do-It-Yourself Spray Painting:

There are some bad things that can happen when large amounts of paint are sprayed without the use of a proper paint booth:

Explosion and/or Fire: Many automotive paints are oil-based and use volatile solvents such as lacquer thinner. When these paints are sprayed, the solvent can be explosive. Keep away from open flames or hot surfaces. For example, I've heard of an explosion and fire happening when lacquer-based paint was sprayed in the presence of halogen lights, which get very hot. Spray painting requires lots of ventilation.

Health Risks Of Paint Fumes: Petroleum solvents can make you feel light-headed, but the bigger problem is that solvents dissolve the fatty myelin around your nerve cells. Myelin acts as electrical insulation for your nerves and brain, and when this stuff dissolves your brain can short-circuit. You wouldn't melt the insulation on the wiring in your car, would you? Don't do it to your brain!

If you paint indoors, wear an organic vapor respirator. I bought one for about 40 bucks at Home Depot. These things use activated charcoal filters to absorb all the volatile organic compounds that pass through them. Eventually they get plugged up and the filters need to be replaced. I store my respirator in a sealed Ziploc bag when not in use.

Overspray: Even with an HVLP (High Volume Low Pressure) spray gun, there is still plenty of overspray. If spraying indoors, the overspray can cover large portions of your garage. If spraying outdoors, the overspray can fall on cars parked nearby. If you cover your neighbor's house or car with paint overspray, you may be held liable for damages. Sometimes overspray wipes off like dust, but sometimes it sticks really well. Watch the direction of the breeze, and observe how far the overspray is travelling.

 

 

More Info:

Tools Used:

  • HVLP Spray Gun
  • Organic Vapor Respirator
  • Air Compressor
  • Sawhorse
  • Lint-Free Towels
  • Ventilation System

Materials Used:

  • Metal Prep
  • Wax and Grease Remover
  • Automotive Primer: Matrix MP480 Epoxy Primer
  • Automotive Paint: Matrix Single Stage Red #73218

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Written April 10, 2008