Spray Painting

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SYBEX Sample Chapter

PC Chop Shop: Tricked Out Guide
to PC Modding
David Groth


Chapter 8: Painting




Copyright © 2004 SYBEX Inc., 1151 Marina Village Parkway, Alameda, CA 94501. World rights reserved. No part of this publication
may be stored in a retrieval system, transmitted, or reproduced in any way, including but not limited to photocopy, photograph,
magnetic or other record, without the prior agreement and written permission of the publisher.

ISBN: 0-7821-4360-1

SYBEX and the SYBEX logo are either registered trademarks or trademarks of SYBEX Inc. in the USA and other countries.

TRADEMARKS: Sybex has attempted throughout this book to distinguish proprietary trademarks from descriptive terms by following
the capitalization style used by the manufacturer. Copyrights and trademarks of all products and services listed or described herein
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This document may contain images, text, trademarks, logos, and/or other material owned by third parties. All rights reserved. Such
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The author and publisher have made their best efforts to prepare this book, and the content is based upon final release software
whenever possible. Portions of the manuscript may be based upon pre-release versions supplied by software manufacturers. The
author and the publisher make no representation or warranties of any kind with regard to the completeness or accuracy of the
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Sybex Inc.
1151 Marina Village Parkway
Alameda, CA 94501
U.S.A.
Phone: 510-523-8233
www.sybex.com
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Chapter Contents
Paint Basics
The Painting Process
Painting Plastic
Painting
Let’s face it. The number one, all-time, largest
reason why people get into case modding is that
they didn’t like the idea of having a plain white or
beige case like everyone else’s. To that end, many
people started painting their cases different colors.
There are so many colors and color schemes that
the chances of having two cases exactly alike (or
even similar) are staggering.
But painting a case is not like painting any other
item you’ve ever painted. There are special tech-
niques and considerations—this has to be a work-
ing computer when you are finished, after all. In
this chapter, you’ll learn all the different things
that need to be done when painting computers
and their parts and what constitutes good paint-
ing practices and techniques.
8
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Paint Basics
Before you even pick up a spray can or gun, before you pick out a color, you need get a
few of the paint basics down. These include:
• Paint chemistry and terminology
• Paint types
• Paint delivery
Paint Chemistry and Terminology
What?! Chemistry?! In a computer book? Yes, you’re going to have to know a bit about
chemistry in order to do successful paint jobs. In addition, you’re going to learn some
of the specialized terminology of the paint and auto body world.
RTS
RTS stands for “ready to spray.” This is paint that you buy at the hardware or auto-
body supply store, take home, and spray. No special mixing or additives are needed.
Most paint already in spray cans can be considered RTS. Also, most auto-body sealers
are RTS (more on them later).
1K
1K is an abbreviation for single stage, which means you mix the paint with one other
chemical (usually a solvent of some kind) and apply it. Most primers are single stage.
2K
2K is an abbreviation for two-stage. This means that you mix the paint with two other
chemicals—in addition to a solvent, you will add some sort of hardener or catalyst to
the mix. Most urethane primers are 2K primers.
Adhesion Promoters
Adhesion promoters are special chemicals that are applied to substrates like plastic that
normally don’t accept paint at all because of their makeup or properties (like flexibility).
Adhesion promoters are sprayed on to ensure that whatever is sprayed on top (usually
a primer of some kind) will stick. They are usually clear or light colored.
Primers
A primer is a special type of paint that does one main job: it provides a uniform sur-
face that promotes adhesion of the paint to the bare metal or other substrate. Generally
speaking, you could put paint on bare metal. But chemically speaking, the two aren’t
all that compatible in the long term. A primer is designed to be the middleman between
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paint and metal. Primer adheres very well to metal. At the same time, it can fill in the
minor surface imperfections to make a smoother overall finish.
There are three different types of primers:
• Primer surfacers
• Acid etch primers
• Polyester primers
Primer surfacers are the most popular types of primers. When you buy a can of
paint for metal that just says “primer” or “acrylic primer,” you are most likely buying
a primer surfacer. Primer surfacers, in addition to doing the standard primer function
of acting as intermediary between paint and metal, are also very thick and will fill
minor surface imperfections and can be sanded perfectly smooth. In auto-body work,
body work is usually done first; then multiple coats of primer surfacer are sprayed on,
allowed to dry, and then block sanded smooth. This procedure is done multiple times
to get the flattest surface possible before any color is applied.
I can’t stress enough that the better your primer and priming application, the
better the overall job is. Painting is easy—it’s the body work and priming that are hard
to get perfect.
An acid etch primer is a very specialized primer. It is typically used over bare
metal and the primer itself contains an acidic compound that helps the primer “bite”
into the metal. Most times, for case modding, you won’t need this kind of primer
(unless you sand all the paint off). It’s mainly used on automotive paint jobs.
Polyester primers are 2K primer surfacers that have a very high solids content.
They are the kings of surfacers. I’ve sprayed these on cars before and I can honestly say
it’s like spraying fill putty. One coat will fill deep sanding scratches. This primer is diffi-
cult to sand properly, and it can settle out quickly when sitting on a shelf. It’s always
best to buy polyester primer the day you need it and have the paint store shake it for
you on their paint shaker so it’s good and mixed.
Sealers
A sealer is a very special type of paint supply. If you have done a lot of body work
under primer or have an old finish that you want to put a new finish on, a sealer is the
chemical barrier between the primers below and the paint above. If you don’t use a
sealer, the solvents from the paint can penetrate the primer and cause the underlying
Note: Primer surfacers can be broken down further into single stage and two stage. By and large, the
cheaper ones are single stage and the more expensive, higher-quality ones are two stage.
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body work to show through (or cause the sanding scratches in the body work to swell
and show).
Some sealers come as RTS, 1K, or 2K. Some shops refer to sealers as primer
sealers. Whatever the case, the sealer is the last coat applied before paint, and you do
not sand it.
Paint Formulations
When you buy paint and paint products (like primers and sealers) it is important that
you know the primary formulation so that you are consistent with whatever formulation
you choose for all the products you will be using. For example, if you use lacquer
paint over an enamel finish, the “hotter” solvent in the lacquer can eat through the
enamel and cause blistering and other finish quality problems.
There are four main types of paint formulations you will see when buying paint
products:
• Acrylic lacquer
• Acrylic enamel
• Acrylic urethane
• Base/clear systems
Acrylic lacquer is one of the older paint formulations—it’s been around since
the ‘60s. Lacquer is special because it dries when its solvents evaporate instead of by a
chemical reaction. It is extremely easy to paint with because of its very fast drying time.
The solvent in acrylic lacquer evaporates so quickly that usually by the time you’re
done painting a case, the first part of the case is dry already. Also, it’s cheap and easy
to fix problems with and will buff to a very high gloss.
There are some disadvantages, though. The solvent in acrylic lacquer (i.e., lac-
quer thinner) is volatile and will dissolve almost anything. If you choose acrylic lacquer
as your paint type, you must make sure all of the components (primer, sealer, etc.) can
withstand the power of the solvent in the paint.
Also, lacquer is not very durable. It chips with the least amount of effort. Very
few cars are painted with lacquer anymore (partially because of the hazardous nature
of lacquer, but also because of its lack of long-term durability).
Note: If you are using a good quality 2K primer, you shouldn’t need a sealer on a small job like a case mod
paint job, unless you’ve got a lot of body work.
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To help you determine if a paint is lacquer, Table 8.1 details some of the more
common paint manufacturers and the trade brands of their acrylic lacquer products.
ǠTable 8.1: Common Brands of Acrylic Lacquers
Manufacturer Trade Name
DuPont Lucite
PPG (Ditzler) Duracryl
Martin-Senour (NAPA) Acrylic Lacquer System
BASF Alpha-Cryl
Akzo-Nobel (Sikkens) Autofine
Krylon Krylon Lacquer
Dupli-Color Dupli-Color Acrylic Lacquer
Acrylic enamel has also been around for quite some time. It has the benefits of
large color selection, high gloss, relatively low cost, resistance to chipping, and ease of
application. Enamel differs primarily from lacquer in that it cures (it doesn’t “dry” per
se). The solvents remain in the paint after application, save for a little evaporation. The
paint cures by a chemical reaction that takes place in the paint. Acrylic enamels take a
long time to fully cure in the open air, often days. In automotive paint jobs, the curing
process is often sped up in heated paint booths.
Table 8.2 lists some of the major manufacturers and their acrylic enamel brands.
ǠTable 8.2: Common Brands of Acrylic Enamels
Manufacturer Trade Name
DuPont Centari
PPG (Ditzler) Delstar
Martin-Senour (NAPA) MS Acrylic Enamel or Crossfire Enamel
BASF (R-M) RM Acrylic Enamel
Akzo-Nobel (Sikkens) Autocryl Enamel
Krylon Krylon Acrylic Enamel
Dupli-Color Duplicolor Acrylic Enamel
Note: Most canned aerosol paint spray cans that you buy (e.g., Krylon) are acrylic enamels, although
there are a few lacquer-based products in aerosol cans.
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One of the newer technologies in automotive refinishing is the acrylic urethane.
It offers the speed and ease of use of lacquer with the durability and catalyzed curing
of enamel. It is more expensive than enamel but just a little more so. Acrylic urethane
is one of several reasons that lacquer and enamel aren’t used much at all anymore in
the automotive refinish business.
Of course there are drawbacks to urethanes. First of all, unfortunately for the
case modder, they aren’t readily available in spray cans. You can have it put in spray
cans, but some require a hardener or catalyst that causes the paint to harden in the
spray can, so the paint has to be used the same day.
Also, many urethanes contain isocyanates (a chemical used in the polymeriza-
tion/curing process). This chemical is a known carcinogen and causes serious health
issues if inhaled.
Table 8.3 shows the brands of some of the more common single-stage ure-
thane paints.
ǠTable 8.3: Single-Stage Urethane Trade Names
Manufacturer Trade Name
DuPont ChromaOne
PPG (Ditzler) Delthane or Concept
Martin-Senour (NAPA) Crossfire Urethane
BASF (R-M) R-M Urethane
Akzo-Nobel (Sikkens) Autocryl Urethane
Krylon N/A
Dupli-Color N/A
One of the most commonly used paint types isn’t really a formulation per se, but
rather a system of paint products used together. This system is known as a base coat/clear
coat (BC/CC) system, or base/clear system. It consists of a urethane base coat to provide
color, followed by a urethane clear coat to provide the shine. This clear coat can be
buffed to a high gloss and provides excellent holdout against damage. Also, metallic
paints lay down better and graphics are much easier to do because you can get the
gloss after the graphics are all finished.
Note: It is possible to speed up the curing time of acrylic enamel using special additives that catalyze the
chemical reaction, making it dry much faster.
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The major disadvantage to these systems is cost. In a standard base/clear system
there are no fewer than six products that must be mixed together: base color, base
reducer, base activator, clear coat, clear activator, and clear reducer. Each of these
products can get expensive in a hurry. Also, the clear coat from most manufacturers
contains isocyanates.
There are both acrylic enamel and urethane BC/CC systems, but the most com-
mon are urethane based. It is possible to do a BC/CC paint job using the acrylic enamel
products found in spray cans, but you’ll need to do more finishing work after the paint
has dried.
Table 8.4 lists some of the names of the more common BC/CC systems used in
automotive painting.
ǠTable 8.4: Base Coat/Clear Coat System Names
Manufacturer Trade Name
DuPont ChromaSystem
PPG (Ditzler) Deltron DBC/DCC
Martin-Senour (NAPA) TEC-Base
Krylon N/A
Dupli-Color N/A
Automotive Paints
One quick item of note: I always like to use automotive paint when painting cases. It
lays down nicer, it lasts longer, and you end up with a more professional look to the
case. Automotive paints are generally not available for sale to minors, so if you are
underage, you’ll have to have a parent help you with these products as they can be
dangerous.
Automotive-grade paint is designed to be sprayed on using paint spray equip-
ment. This equipment finely atomizes the paint and gets it to “lay out” smoothly. If
you don’t have access to this equipment, you’ll need to either borrow or rent it, or
use aerosol spray can paint instead.
Note: Keep in mind that this section is about the different types of paints that could be used to paint a
case. It may not always be feasible (cost-wise).
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Paint Delivery
Now that you know the major types of paint, we can discuss how best to get those
paints on the parts you need to paint. For the home hobbyist, there are two main
methods of painting: the spray can and the spray gun. Both methods take the paint
and atomize it—that is, they break the paint up into a fine mist that can be directed at
a part. The finer this mist is, the more even the paint job is and the nicer it will look.
But each method differs in the way this process is done and how efficient (and costly)
the method is.
Spray Can
Most likely, everyone has used a spray can at some point in their life. A spray can is
paint, thinner, and propellant (the gas that gets the paint to come out of the can) all
contained in a single, nonrefillable can. There is usually sufficient paint in the larger,
11–12-ounce cans to paint an entire case.
These spray cans (often called “spray bombs”) do a remarkable job for as cheap
as they are (usually under $5 each). Plus, many stores will put automotive quality paint
into a spray can for you. It’s more expensive, but if you don’t have a spray gun, it’s
worth it.
Spray Gun
If you are painting with automotive-grade paint, you will definitely need a spray gun.
A spray gun uses compressed air from an air compressor to atomize the paint in the
gun. Spray guns come in many different types, and a complete discussion is outside the
scope of this book. Just know that you can find some good values at your local Sears
or Harbor Freight. If you plan on doing a lot of painting, get the best gun you can
afford; you’ll thank me later. Figure 8.1 shows an example of a spray gun.
Note: I’ve had excellent results with my Sharpe Platinum HVLP spray gun. It isn’t the least expensive, but
it’s not the most expensive, either. I’ve also had good success with their Cobalt line. Check out their product
line at www.sharpe1.com.
Note: Keep in mind that in addition to buying a spray gun, you’ll need a compressor capable of keeping
up with the spray gun (a fairly large one), as well as an air hose, respirator equipment, and a proper place to
use it (a garage or other area separate from the house).
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The advantages to painting with a spray gun are that the paint lays out much
nicer and covers quicker (fewer coats are needed). Plus, you can control the paint spray
better than you can with the limited nozzle on the spray can. Finally, the variety of
paint materials you can spray is also much greater.
Painting Supplies
In addition to the paint, there are a few supplies you may need for doing paint and
body work on your case.
Body filler applicators These are small rubber or plastic squeegees you use to apply
body filler. You can find them in any store that sells auto-body supplies (and even in
Wal-Mart’s automotive section).
Figure 8.1 A typical spray gun
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Mixing board This is a special Masonite board with a large pad of paper installed. It is
used for mixing small amounts of body filler and provides a clean surface on which to
mix it. As you finish using it, you tear off the used portion and are presented with a
new, clean surface.
Mixing cups If you are using automotive paint, you will need mixing cups. They are
cheap and you can even get a couple for free from the store where you buy your paint.
They are graduated on the side and will allow you to mix the paint properly.
Stir sticks These are also available from your paint supplier for free. They are simply
pine sticks to stir paint with. You can throw them away when you’re finished.
Tack rags These are just cheesecloth rags embedded with pine tar resin and are used
for removing final traces of dust and dirt before painting.
Nitrile gloves These are gloves that are solvent-resistant and are good for using while
mixing paint to prevent getting paint on your skin. Lacquer thinner will dissolve them,
however. You can buy a box of 100 for around $6.
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Cleaning thinner (lacquer thinner) This is nothing more than cheap lacquer thinner
and should be used only for cleaning paint guns, cleaning surfaces, etc. (it should not
be used for painting). You can usually buy five gallons for around $20.
Paint strainers These are special paper funnels for pouring paint into a spray gun.
They strain out any foreign material that may have fallen into the mixing cup during
mixing. They should be free from your paint supplier (although you might have to ask
for them).
Masking tape This is special tape that sticks well and will not leave a residue when
pulled off. 3M arguably makes the best masking tape. Don’t get cheap stuff or your
work will suffer. Plus, the difference between the good stuff and the cheap stuff is a
buck or two per roll. It comes in several thicknesses and is used to tape off things you
don’t want paint on.
Masking paper This is special paper used during painting to keep paint off of areas you
don’t want paint on. It is nonporous and will not get paper lint into your paint job.
Wax and grease remover This is a special chemical you use before painting to remove
traces of wax and grease (and other oils from your skin) that might cause defects in the
paint job.
Lint-free paper towels These are special paper towels (like the DuPont Sontara line)
that do not leave lint behind when used on painted surfaces.
That’s the majority of the items you’ll use when painting. You may not need all
of them (you may only need the masking tape, paper, and tack rags), but it’s good to
know what else you might need to buy before you do your paint job.
Where to Paint
When painting anything—cases, cars, etc.—it’s a good idea to have a well-ventilated
area. That’s why professional painters paint in a paint spray booth that has lots of
lighting and a ventilation system that can change out the air multiple times per hour.
Obviously, the home hobbyist cannot afford to put a paint booth in their garage
(unless you are truly insane like me). However, it is possible to get adequate airflow
by opening the overhead door and any windows to get cross ventilation going.
In addition to ventilation, you want to have an area to put your parts while they
are being painted so the overspray (a term for the extra paint dust that seems to get all
over everything) won’t land on anything you care about. Plus, you need to be able to
support the parts so you can paint all sides of a part. I like to hang what are commonly
known as bicycle hooks from the joists in my garage ceiling and suspend parts from
these using thick wire (about half the diameter of coat hanger wire).
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Finally, the area you are going to paint in should be clean. Try not to paint in
the same area you create dust. A separate room is ideal, but at the very least, try to paint
across the room from that area. And, while it is a good idea to clean before you paint,
remove the parts from the area you are cleaning so the dust you kick up with the broom
doesn’t land on your freshly cleaned parts. After the dust settles down, bring the parts
back in and clean them (again) before painting.
The Painting Process
Now that you have a good handle on the basic types of paint, their differences, and
how they relate to case painting, you are ready to learn about the basics of the painting
process. The six basic steps (one of which is optional) are
• Step 1: Surface Preparation
• Step 2: Priming
• Step 3: Sanding
• Step 4: Sealing (optional)
• Step 5: Painting
• Step 6: Finishing
Step 1: Surface Preparation
Before the actual painting begins, it is important to properly prepare the surface to be
painted. If the metal you are going to paint already has paint on it (and most cases do),
it is beneficial to prepare that surface to accept paint. Most generic cases are painted
with a kind of splatter paint at the factory. This is a very uneven surface and makes for
a poor substrate for painting. You can paint over this surface, just make sure to level
off the bumps with 220 grit sandpaper on a sanding block first. My personal prefer-
ence is to sand this splatter paint completely off of metal and get the surface to bare
metal before painting. The paint will stick better, and you won’t have to worry about
compatibility problems. Plus, I think the job turns out better overall.
The fastest way to remove all this paint is with a D/A sander and 80 grit sand-
paper (see Figure 8.2).
The sander can be either pneumatic or electric, as long as it does the job. I find
that a pneumatic D/A sander makes quick work of the job with a minimum of paper
changes. Put on your eye, ear, and breathing protection, load up your sander with 80
grit, then work slowly back and forth across the case.
Warni ng: When working on plastic do not use 80 grit! You’ll scratch the surface severely.
Use 220 grit.
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Figure 8.2 Sanding off the old case paint
Once you have removed all the paint, you are almost ready to move on to the
next step. In order to properly prepare the substrate, you should sand the surface with
220 grit paper to make an even surface of scratches so the primer has something to bite
into. Just change the paper on the sander to 220 grit and make a couple passes over the
surface. Finally, clean any sanding dust away with compressed air, followed by wax
and grease remover (found at any paint supply store).
Plastic filler, or Bondo as it is more commonly known, is a great tool for work-
ing on cases. It is essentially a catalyzed plastic resin that hardens after a few minutes
when the two components are mixed. There are three types:
Standard filler Standard filler is used for filling in surface imperfections less than
1
/8
in depth. If you try and fill in too large of a gap or a gap that flexes, a crack will
develop. When people think of plastic filler, this is what they think of. It comes in
many different colors by many different vendors, but the one most people think of
is the Bondo brand.
Note: When sanding the front plastic case bezel, sand off any detail castings (like the little symbols next
to the power and reset buttons). They won’t paint well anyway.
Warni ng: Be careful when sanding sheet metal that you don’t stay too long in one spot, causing the
metal to overheat and warp.
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Kitty hair Kitty hair is fiberglass-reinforced plastic filler. It is essentially standard filler
with strands of fiberglass embedded throughout. Use it whenever strength needs to be
considered. It should never be used as a structural member, just as a foundation where
multiple cracks have been filled and you need a bit of extra strength.
Finishing butter Finishing butter is an extremely thin and smooth plastic filler. Use it to
fill the sanding scratches left by sanding the other two types of filler. It has little or no
strength to it and should never be used to a depth of more than
1
/32 .
Figure 8.3 shows an example of the three types of filler (uncatalyzed). Notice the
difference in consistency.
Figure 8.3 The three types of plastic filler
Procedure: Using Filler to Fill Imperfections in a Case
You may have an item in your case that has an imperfect seam or something you’d like to blend
just a little better. This procedure shows you how to use filler to fill some small bodywork you’ve
done on a case.
Items Needed
• Standard filler
• Mixing surface (a clean piece of glass or plastic will work)
• Paint stir stick
Continues
Kitty hair Standard filler Finishing butter
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Procedure: Using Filler to Fill Imperfections in a Case (continued)
• Filler applicators (different sizes)
• Multiple sandpaper grits (80, 220, 360) and a sanding block
• Wax and grease remover
• Lint-free paper towels
Procedure Steps
1. Grind or sand the surfaces using 80 grit (220 if using plastic) so that the filler will be adher-
ing to a smooth surface.
2. Clean the surface thoroughly using wax and grease remover to remove any oils or dirt that
might get trapped under the filler and cause it to lift later.
3. Using a stir stick, remove some filler from its can and put it on the mixing surface.
4. Squirt a small ribbon of catalyst from its tube onto the filler. The more catalyst you use, the
less time it takes for the filler to cure. Follow the directions that come on the package of filler
you are using to figure out the ratio of catalyst to filler. Use the stir stick to mix the two
together to an even color.
Continues
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Procedure: Using Filler to Fill Imperfections in a Case (continued)
5. Move immediately to the work area and start spreading the filler onto the work piece using a
filler spreader. If you need to put it on thickly, don’t put it all on in one coat. Use several
smaller coats, sanding in between.
6. Wait for the filler to harden.
7. Start sanding the filler using 80 grit (220 if working on plastic) and a sanding block. Sand
until the filler has a uniform level with the surrounding work piece. Repeat steps 5–8 if nec-
essary to obtain a level surface.
8. Sand the repair with 220 grit. Run your hands across the piece with your eyes closed. When you
can’t tell where the metal ends and the repair begins (this is called a feather edge), you’re finished.
9. Clean the surface.
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Step 2: Priming
As already mentioned, primer is the coat that sits between the metal and the paint and
provides filling and adhesion assistance for the paint. Now that you’ve got all the
bodywork done and the metal surface is properly prepared, it is time to prime.
Before you actually spray the primer, though, make sure that the surface is cleaned
properly with wax and grease remover (as mentioned earlier).
Depending on which type of primer you are using, you’ll probably need to mix it
(assuming you are using auto-body primer). In the case of spray cans, the paint comes
RTS in the cans.
Procedure: Priming a Part with Spray Cans
Now that your parts are properly prepared, you are ready to put primer on them in preparation for
paint. Some people overlook this step, but if you don’t prime the parts you are painting, the finish
won’t last as long and it will chip more easily. This procedure will show you how to properly prime
a part using a spray can primer.
Items Needed
• Primer (compatible with the type of paint you will be using)
• Tack rag
• Wax and grease remover
• Hooks and wire (for supporting parts)
• Paint respirator and nitrile gloves
Procedure Steps
1. Properly prepare the parts that you want primed (as described in “Step 1: Surface Prepara-
tion”). Mask off what you don’t want primer on. Hang the parts to be sprayed so that you can
spray in all the cracks and crevices. I like to hang my parts from the ceiling with hooks and
wire coat hangers because it allows me to spray them without dust kicking up from whatever
surface the parts might rest on. However, any flat surface will do to support the parts.
Continues
Note: Choose a primer that is compatible with the final finish you intend to spray and buy it from the
same manufacturer (they will have recommendations on which primers to use).
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Procedure: Priming a Part with Spray Cans (continued)
2. Wipe the part down one last time with wax and grease remover and allow it to dry. This
removes any traces of fingerprint grease or other oily contaminants from the previous user’s
hands. Then open the tack rag and wipe the part down again. Remember, when painting,
there is no such thing as too clean!
3. You are now ready to spray the primer. Take the top off the primer can and shake thoroughly
for three minutes (or according to directions on primer can).
4. Put on your paint respirator and nitrile gloves and begin spraying the primer. Hold the can
about 6–8 inches from the surface to be painted (but pointing right at it at a 90 degree
angle). Push the button on the can, make a pass across the part, and then let go of the but-
ton. Never just point the can at the part and start spraying. You will get thick areas of paint or
primer. If you go too slowly, the primer will run; go too fast, you’ll have dry areas. With primer,
it’s better to have lots of thin coats than to have one thick coat. It will take practice, but the
more you do it, the better you get!
Continues
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Procedure: Priming a Part with Spray Cans (continued)
5. Make another pass across the part, overlapping the spray passes by 50 percent.
6. Continue making passes across the part, until the entire part is covered.
7. Wait 10 minutes for the primer to flash dry.
8. Repeat steps 4–7 two more times so you have three complete coats of primer on each part.
Remember that even the best paint jobs will look terrible with a bad primer job underneath,
so take your time!
9. Allow to dry overnight before handling.
Note: If you are going to prime with automotive primer, the same steps apply. Just mix the primer
according to their directions and apply with your paint gun. You will need fewer coats, however, and use less
paint overall.
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Step 3: Finish Sanding and Cleaning
Now that you have the part primed and it has dried sufficiently, you are ready to block
sand the part to create that perfectly flat surface that looks absolutely stunning on a
case. Mirror-like cases don’t come from just having glossy paint, but having perfectly
flat surfaces as well. Ask any painter—they’ll say 95 percent of the quality of a paint
job is in the preparation and the primer work.
First of all, you’ll need to use a sanding block. Wrap your sandpaper around the
sanding block as shown in Figure 8.4. This will provide a perfectly flat surface to sand
with. Start the first sanding with 360 grit, then move to wet-sanding with 500 grit. To
wet-sand, get a bucket of water with a drop or two of dish soap in it and some wet/dry
sandpaper. Dip the sandpaper and sanding block in this water (or even better, spray it
on the surface and sanding block with a spray bottle). This soapy water will lubricate
the surface and make it easier to sand. Plus, if you keep the surface wet, the water will
help wash away the sanding residue and make the sandpaper last longer.
The proper sanding technique is also important. In order to get a perfectly flat
surface, you need to sand in a cross-hatch pattern (as shown in Figure 8.5). First sand
the entire panel using long strokes in one direction, then sand 90 degrees to the first
direction. Use this technique as many times as necessary to obtain a flat surface. If you
sand through the primer (which does happen very easily on the edges of the case or any
ridges), just finish sanding the panel, apply another coat of primer, then resand.
Figure 8.4 Properly using sandpaper with
a sanding block
Note: If you don’t have a sanding block, you can wrap sandpaper around a paint stir stick or block of wood.
Just make sure the sandpaper completely covers the block so you don’t put deep gouges in your fresh primer.
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Repeat this until the panel is completely flat, has a complete coat of primer, and
is almost shiny (the 500 grit wet-sanding will put a slight gloss in the primer), so the
panels look like the one in Figure 8.6.
Figure 8.5 Proper primer sanding technique
Figure 8.6 Finished block sanding and ready to paint
Sand with
perpendicular
strokes
Note: If you want the best paint job possible, you should prime and block sand at least three times, if not
more. The more you do this, the flatter it gets, and the more mirror-like the finish will be.
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Step 4: Sealing
This step may be optional, depending on the formulation of the paint you are using
and how much body work you have done. Sealer sprays and looks just like the primer,
but you don’t sand it. It is just a barrier coat between the paint and primer to prevent
the solvents in the paint from lifting any bodywork. If you have properly applied a
good quality 2K primer over your bodywork, a sealer should not be necessary.
Also, generally speaking, if you are spraying with spray cans, a sealer is not
needed, as long as you are using paint and primer from the same manufacturer. You
could do use it as an extra precaution, though.
To seal the part, just clean the part after sanding with wax and grease remover,
tack it off, and spray the sealer. You really only need one full wet coat of sealer for any
paint job. Applying more is just wasteful. A wet coat is when the paint looks wet as
you apply it. If you are holding the can too far away or move too fast, you won’t get a
pass that’s wet.
Some sealers, called wet-on-wet sealers, are designed to be applied and then
immediately painted over. The paint and sealer cure simultaneously, forming an
extremely strong bond. Others you must allow to fully cure first (usually 4–6 hours)
before painting over.
Note: It is extremely important that the cleaning be thorough for this step. If not, you may get contami-
nations caught in the paint that will get painted over. If this happens, you can lightly sand these dust “nibs”
after the sealer has a chance to cure and then respray the sealer over the repair area.
Note: As with primers and paints, choose a sealer that works with both so that paint compatibility prob-
lems don’t cause problems with how the finish looks or lasts.
Note: If you need help telling whether or not the panel is perfectly flat, use a guide coat, which is nothing
more than a thin coat of a contrasting color primer. Use a coat of black primer on top of a gray primer for
example. When you block sand, try to sand all the guide coat off using the cross hatch technique described.
High spots will show up with the first pass as light dots (assuming a black guide coat on a gray primer), low
spots will show up as the dark guide coat surrounded by gray primer. A guide coat will help you obtain a per-
fectly flat surface.
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Step 5: Painting
Whew! You’re finally ready to start painting!
First of all, put on all your protective gear (respirator, gloves, etc.). If you are
using automotive paint, you’ll want to have a full body paint suit made of Tyvek (a
nonporous material that is very durable and very cheap—you’ve seen it as overnight
envelopes from the major freight carriers). Paint fumes are hazardous to your health,
so make sure all your safety equipment is working properly.
Next, hang your parts up to prepare them for spraying (as discussed earlier).
Then, obtain a tack rag and do one final cleaning of the part you are spraying. As I’ve
said before you can never get it too clean! The tack rag is coated in pine pitch and is
designed to pick up and hold any small contaminants that might otherwise ruin your
perfect paint job, including those that might have gotten on the part. Once you have
tacked off the part, do not touch the part or raise any dust. If you do, you’ll have to
retack the part.
Next, assuming you are using spray cans, shake the cans thoroughly according
to the directions on the can. If you are painting with automotive paint, mix your paint
according the manufacturer’s directions. Once the paint is mixed, pour it into your
spray gun (using a paint strainer, of course), as shown in Figure 8.7.
Figure 8.7 Pouring paint into a spray gun
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Start spraying your paint as with the primer: point the paint nozzle at the part
(and perpendicular to the part), start the paint flow, move across the work piece (as
shown in Figure 8.8), and release the paint flow after you have made a pass completely
across the part. Make another pass back across the part in the same method, but over-
lap the first pass by 50 percent. Keep doing this, moving up a little each time until the
entire panel is covered.
After you have put on one coat, wait 15 minutes while the first coat cures (mak-
ing sure not to raise any dust while you are waiting). Go back and put on another, full,
wet coat using the same technique as before. Do this until you have at least three full, wet
coats on the part. Then, allow the part to dry overnight.
If you are using a single-colored paint, you’re done now and can move on to the
next step. If you’re using a BC/CC system, you’ll have to wait 20 minutes (or so) until
the base coat is dry, then you can mix up the clear and spray it as well. Or, if you are
Note: If you have trash in the paint or other imperfections (like runs), don’t worry, you’ll get them out in
the next step.
Note: You may have to make short, quick sprays of paint to get the paint into small nooks and crannies
that a normal pass won’t get adequately.
Note: If you are spraying enamel, spray the first coat fairly quickly so that you put on only a light coat of
paint. This first paint coat is known as a tack coat and will help keep subsequent coats from running.
Figure 8.8 Proper painting technique
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using a spray can, just start spraying the clear coats as soon as the color coat is dry.
Use the same technique, but you may have to move a bit faster because clear coat is
heavier and runs easier.
When you are finished, clean your spray can by turning it upside and spraying
until it sprays clear. Or, if you are using a spray gun, clean the gun with lacquer thinner.
Procedure: Painting a Part (Acrylic Enamel Spray Cans)
Now that you have primer applied to your part, you are ready to paint. In this procedure, you’ll
learn how to paint a case part (could be a case side or door).
Items Needed
• Screwdrivers
• Masking tape and paper
• Sandpaper (220, 360, 500 grits)
• Sanding block
• Acrylic enamel paint in your choice of color
• Primer (compatible with chosen paint)
• Part to be painted
Procedure Steps
1. Disassemble the part and remove anything you don’t want painted. If not removable, mask it
off using good quality masking tape and nonporous masking paper.
2. Prepare the surface appropriately by sanding and doing any filler work, if necessary.
3. Clean the parts with water.
4. Tack the parts clean and spray the primer.
5. Fill any deep scratches, then sand with 220, 360, then 500 (wet/dry) grit sandpaper on a
sanding block.
6. Repeat steps 3–5 until surface is perfectly smooth.
Continues
Note: If you want to have a better overall finish, you can try just spraying a regular spray can color as the
base, then wet-sand, then come back and spray more color, then perform the painting procedures in Step 5,
then go back and apply the paint again and wet sand, then repeat until you have a perfectly flat base color—
then apply the clear coat—but this only works if the base coat is designed to be wet-sanded.
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Procedure: Painting a Part (Acrylic Enamel Spray Cans) (continued)
7. Perform your final clean and tack off.
8. Shake the spray can according to directions on can.
9. Spray a quick mist coat of paint so that every surface has a very light coat. Allow this coat to
tack dry for 15 minutes.
10. Spray on at least three full coats of paint in even strokes, overlapping each pass by 50 per-
cent. Continue spraying until full coverage is achieved. Allow each coat to dry for 15 minutes
before spraying on the next.
11. Let paint dry overnight.
12. Finish as necessary by nib sanding, buffing, etc.
Step 6: Finishing
Most people stop before they get to this step, but this step is the most important. This
is the step that separates the amateurs from the professionals. Finishing a paint job will
take out all the minor imperfections in the paint job and make the entire case glow like
a colored mirror! In this step, you’ll learn how to properly finish a paint job, as well as
what the various imperfections are and how to deal with them.
Finishing Processes
To start off, you’ll notice that the paint job most likely has a slightly mottled appear-
ance (Figure 8.9). This is called orange peel and is a result of varying shop conditions.
Don’t worry, most cars come from the factory with a little orange peel. You also may
have some dust in the paint which will form little paint “mountains.” To fix this, you’ll
block sand the paint job with very fine sandpaper and lots of water to make the paint
job flat and even before you buff it to a high gloss.
Figure 8.9 Orange peel in a paint job
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Procedure: Wet-Sanding and Polishing a Fresh Paint Job
Whenever you have done a new paint job, you’ll want to make it look as perfect as possible. To do
this, remove the slight surface imperfections by wet-sanding the new finish and then buffing it.
You should wait at least two days to allow the paint to cure before trying this process.
Items Needed
• Panel with a new paint job
• Masking tape
• 1000, 1500, and 2000 grit sandpaper
• Sanding block
• Bucket of warm, soapy water
• Lots of cotton towels (fabric diapers work great!)
• 3M Perfect-IT III Rubbing Compound
• 3M Machine Glaze
• Power buffer with foam buffing pads (optional)
Procedure Steps
1. Make sure your paint has cured at least two days and has sufficient paint on it (so you don’t
sand through it).
2. Put masking tape on the very edges of the panels so you don’t sand or buff through them.
Continues
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Procedure: Wet-Sanding and Polishing a Fresh Paint Job (continued)
3. Starting with the 1000 grit sandpaper, wrap the sandpaper around the sanding block and dip
it in the water. Sand the paint flat. Make sure to sand in long smooth strokes. Keep the sand-
paper very wet. When sanding do not use circular motions or cross hatching—these will be
hard to remove later. If you feel or hear scratching, stop! It means a piece of grit has gotten
caught between the sandpaper and the paint and can cause damage as you sand. Rinse off
your sandpaper and the panel and start again.
4. Once you have sanded the panel flat, wipe it dry with a cotton towel and look for dark spots
against the matte finish that you now have. These are low spots, and you will need to keep
sanding to wear the paint down so these are completely gone.
Continues
Low spots
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Procedure: Wet-Sanding and Polishing a Fresh Paint Job (continued)
5. Switch to 1500 grit sandpaper and lightly continue sanding. Repeat this process with 2000
grit to get the panel as smooth as possible.
6. Dry the panels completely with a cotton towel. The panels should be completely flat.
7. Squirt some 3M Perfect-It III Rubbing Compound on the panel you have been sanding.
8. Using either a power buffer with foam compounding pad, or by hand with a clean cotton
towel, work the compound into the paint until the gloss is restored. This will take lots of
elbow grease, and the power buffer is recommended (although it can very easily burn
through the paint).
Continues
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Procedure: Wet-Sanding and Polishing a Fresh Paint Job (continued)
9. Wipe off any remaining compounding residue.
10. Apply machine glaze to the panel and work it in as before with a new clean cotton towel. If
using the power buffer, switch to a foam polishing pad and go slow.
11. Use another clean cotton towel to wipe the residue from the panel and polish it to a high gloss.
12. After about a month, you can wax your case with a fine Carnauba wax. Until then, just keep it
clean with soap and water (when it’s powered off, of course).
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Paint Imperfections and What to Do about Them
There are, of course, lots of things that can go wrong with a paint job. In this section
you’ll learn what they are and what to do about them. Table 8.5 lists the most com-
mon paint problems you’re likely to see and what to do about them.
ǠTable 8.5: Common Paint Problems and Solutions
Problem Cause Solutions
Oil/grease/silicone on surface Sand problem area, wipe well with wax and
grease remover, and respray.
Wet-sand and buff.
Runs Spraying too close/too slow Sand out and respray (and adjust spraying tech-
nique). You can also buy a special file that will
“shave off” the runs so they can be buffed down.
Keep environment clean while painting. Nibs can
be sanded and buffed out after paint has cured.
Bugs in paint Use a toothpick to pick the majority of the bug
remains out of the finish while the paint is still
tacky. Sand/buff as you would a dust nib.
Wait until humidity is below 50 percent or spray
in climate controlled area.
Painting Plastic
The main difference between painting metal and painting plastic is that plastic will
absorb the paint differently. If you look closely at the plastic parts of a computer case,
you will notice that the parts have a texture to them left over from the production
process. This texture must be sanded smooth in order for the case to accept paint prop-
erly. This is the same technique we discussed earlier in the book regarding painting key-
boards and mice.
In addition to sanding plastic smooth, you’ll need to make sure you don’t use
too coarse of a sandpaper so that you won’t put deep scratches in it.
Some people have suggested using vinyl dye to paint plastic parts. Yes, that does
work for putting color on the parts. However, you’ll have a difficult time getting it to
match the rest of the case properly. If you properly prepare the surface by sanding with
the right sandpaper grits (as mentioned earlier) and use the right amount of compatible
primer, you can get your plastic parts to accept paint properly (as long as the plastic is
compatible with the paint and won’t be melted by it).
Humidity too high (over
50 percent)
Whitish haze
or streaks
Bugs going where they
shouldn’t
Dusty environment when
painting
Nibs (dust/dirt
in paint)
Improper spray tempera-
ture or pressure
Orange peel
Fish eyes (small
pits in the finish)
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