Corvette Body & Paint Repair Basics

Corvette Body & Paint Repair
Basics
by Lars Grimsrud & Butch Powers
SVE Automotive
Restoration
Musclecar, Collector & Exotic Auto Repair &
Restoration
Broomfield, CO
This tech paper will discuss
simple repair (non-structural) and refinishing processes to produce
high-quality results on fiberglass (Corvette) panels. Recognize that
there are many different product lines out there, and several work
techniques for accomplishing body repairs. Different auto body
professionals have different preferences as to how to do things, and I may
get some disagreement on the specifics of this article. This article will
provide you with a group of products and materials, and my personal
technique, for accomplishing first-class results.
General
‘Vette Info
Two different construction techniques have been used
to manufacture Corvette body panels over the years. When the ‘Vette
made its debut, the new “FRP” body was a major innovation.
“Fiberglass Reinforced Plastic” was a construction method that
could be used to make lightweight panels with curves and design features
that could not be easily duplicated in stamped steel. The body was
basically built just like a fiberglass swimming pool or a boat hull: A
“chopgun” was used to blow fiberglass strands and resin into a
mold that was first coated with resin to produce a smooth surface finish
on the body parts. This technique was used through the 1981 model
year.
1982 was a unique transition year in many respects. Fuel
injection was added to the ‘Vette, and a computer was installed to
manage all major engine functions. ’82 also saw the advent of a
revised body panel construction. “Structural Matted
Components,” or SMC panels, were thinner and lighter due to a
laminate construction using more plastic and less ‘glass. This
panel type is used on all of our C4 ‘Vettes, and partially on the
groundbreaking ’82.
The composite materials on all ‘Vettes
require use of specific techniques and materials. Treating a ‘Vette
like a steel car can cause irreparable damage to the body: metal paint
stripping techniques cannot be used, and fillers designed for use on steel
will not adhere properly to the FRP or SMC panels. So read on to get the
real scoop on the right stuff to use….
Tools required
Body
shops use a lot of air-powered tools in order to speed up repairs and
improve profits. All cosmetic bodywork can be performed without the use
of air tools, and you will often get better results due to the slower
progression of the work. You will, however, need a paint gun, and
you’ll need compressed air to power it.
Hand Tools
Needed
File Board
A File Board isn’t a file at all:
it’s a long backing board with handles for mounting long strips of
sandpaper, called “file sheets.” The length and stiffness of
the file board allows you to produce perfectly smooth, straight panels and
repairs. It’s the most important tool you’ll use in the
repair and refinishing of your ‘Vette. The most common Boards are
molded hard rubber, and require use of sticky-backed sandpaper. I
personally prefer the old style wooden ones with metal clips securing the
sandpaper: they allow me to use either sticky-backed or standard
sandpaper. Cost of a wooden File Board with clips is about $25. They are
available at all body and paint supply stores. The long ones, which I
highly recommend, are 16″ long and 2-1/2″ wide.
Sanding
Block
In addition to your File Board, you’ll need a small, rubber
sanding block. These soft, flexible black rubber blocks are about
3/8″ thick, and measure 2-1/2″ wide by 5″ long. These
dimensions allow you to tear a piece of standard sandpaper in half and
wrap it perfectly around this semi-flexible block. You’ll use it to
do all of your finish sanding and color sanding (discussed
later).
Filler Handling/Mixing Tools
To mix and apply any body
fillers, you’ll need a flat plate and a spatula/spreader. Flat
plastic/nylon mixing plates and spreaders are available from your body &
paint supply store, but I just use a flat piece of aluminum plate that
measures about a foot square, and the paint supply store gives me a
handful of the low-cost yellow plastic spreaders.
Paint Mask
All
of the paint supply places carry low-cost, disposable, cartridge-type
paint masks. They work great, you don’t have to throw them away
after use, and they’re cheap. Get one.
Power Tools
Needed
Paint Gun
A topic all to itself, paint guns come in a
huge range of qualities, types, and prices. For home use, there are two
basic types: Suction Feed and Gravity Feed.
The Suction Feed gun is
the paint gun we’re all used to seeing: it has a detachable paint
cup slung underneath, and operates by siphoning the paint up from the cup
and into the discharge nozzle. These are the most economical guns, and
can produce quite acceptable results. Economy versions, which are
spin-offs and near-duplicates of the top-end name-brand guns, can be found
at Buyer’s Club, Eagle Hardware, Pace Membership Warehouses, and
other hardware stores. Prices range from about $25 – $75. I have
actually painted complete cars with a $35 siphon feed generic paint gun
with outstanding results. Disadvantage of these econo-guns is that they
cannot be rebuilt (replacement parts are generally not available), you
cannot change nozzle and tip sizes (various sizes not available), and they
wear out faster than the high-end name-brand guns. I still have my $35
gun that I bought over 10 years ago, and my son is now using it to paint
his car. There are also name-brand, better-quality siphon feed guns made
by Snap-On, Devilbiss, Sharp, and others. These guns can be rebuilt
indefinitely, lots of parts are available, and they produce excellent
results. Overall disadvantage of the siphon feed guns is that not all of
the paint in the paint cup is usable: they will quit spraying while there
is still �” of paint in the cup. Also, as paint level gets low,
they will occasionally paint intermittently as the siphon tube is
uncovered during the painting process. Clean-up is a bit of a mess, as
there will be some paint to dispose of. Yet, I would recommend one of
these econo-guns to the beginner, as they will perform quite well for the
$$.
The gravity-feed gun is what is primarily used in the industry.
Most of the gravity feed guns are also what are known as “High
Volume Low Pressure,” or “HVLP.” The key characteristic
about these guns is that the paint cup is mounted on top of the paint gun
instead of underneath. This produces a very uniform flow of paint to the
discharge nozzle, allowing use of lower air pressure (and lower paint
emissions from overspray). It also allows all of the paint in the cup to
be used, and simplifies cleanup. Good, econo-versions are available, but
at a higher price than the econo-version of the siphon feed guns. All of
the major paint gun manufacturers make gravity feed guns, and they are
excellent quality. We use them exclusively at our restoration facility,
but I still use my siphon feed guns at home. If you have $200 to spend,
buy a gravity feed instead of a siphon feed.
Compressor
Here you
want something that will keep up with your paint gun and not drop off
significantly in pressure while you’re painting. This requires at
least 5 horsepower. I’ve seen guys do it with 3-horse, but it
won’t keep up continuously with a paint gun. If you have a 220-volt
outlet in your garage, go with the 220 power, otherwise you’ll have
to do with a 120-volt unit. Compressors of this size are always on sale
at the big hardware chain stores. Look for a deal. I’ve been
running a 5-horse, 120-volt Craftsman for the past 15 years with great
success. I can sure tell on my utility bill when I’m painting a
car, though…
Buffer
To finish off your paint job,
you’ll need to be able to buff it out. Don’t do this by hand:
Get an electric buffer. Your paint supply store can then sell you a good
foam pad to go on it.
Consumable Supplies
These are the basic
consumables you’ll need no matter what kind of car you’re
doing:
Econo-Grade Lacquer Thinner
For general clean-up, get at
least a one-gallon can of the econo-grade stuff. You’ll use it to
clean up your filler application tools as well as your paint gun. The
paint supply stores actually sell stuff labeled as econo-grade thinner,
and it’s cheap. Any more, I buy it in 5-gallon cans even for home
use.
Paper Towels
Pick up a three-pack: you’ll be blowing
through paper towels like you won’t believe for all your clean-up
work.
Sandpaper
You’re going to be surprised how much $$
you’ll spend on sandpaper.
First, you’ll need a few
different grits for your File Board. These are available in pre-cut
lengths in boxes with 50-or-so sheets per box. But if you want to save
about 50% on costs, you can buy the sticky-backed file sheet paper in
uncut rolls that are 2-1/2″ wide and cut it to length yourself. If
you’re as cheap as me, you go for the rolls, and steal your
wife’s kitchen scissors to cut them to length. Here’s what
you need:
1 roll 80-grit
1 roll 150 grit
1 roll 220 grit
Then
get a ream of regular 600 grit wet-or-dry and a pack of 1500 grit
wet.
Each of these items will run you at least $25, so don’t fall
over from the sticker shock…
Masking tape
Get several
rolls. I like to use both the regular �” wide stuff as well as some
of the big, 2″ wide. Don’t buy the really cheap stuff: either
it won’t stick well, or the glue will transfer to your car. I like
the 3M tape products.
Fillers
Since fiberglass flexes and
expands/contracts differently than steel, you don’t want to use just
plain ol’ “Bond-O” on your ‘Vette. There are two
products you’ll need to do a little fixin’ on your
‘Vette.
First, for filling missing chunks and major nicks (damage
that extends through the gelcoat and into the ‘glass structure), you
want to pick up a quart of 3M Short Strand Fiberglass Reinforced Filler,
part number 051131-05815. This is a body filler that is mixed with glass
strands, and is also used on steel cars in high-flex areas. It will do
the major structural filling, but will not produce a fine, closed-cell
surface finish. So for general smoothing and filling, like finishing off
the Fiberfill and for filling the defects caused by the last body shop
when they sanded the whole car with a D/A sander, use the filler product
line by Evercoat. Evercoat makes a product line for fiberglass cars
called “Plasticworks.” Evercoat 870 is the part number for
the quart can. 880 is the gallon container. It’s pretty cheap,
actually, so I buy it by the gallon. If you need to bond any Corvette
panels for repair or modification, they also make what they call a Vette
Panel Adhesive: The Type 1 adhesive is for the FRP cars. Type 2 is for
SMC or when bonding FRP to SMC. Check with your paint supply store: they
can give you the exact details and applications for the product line. If
you choose other product lines, just make sure that the filler products
are intended for use on, and compatible with, FRP and/or SMC.
Tack
Cloth
A sticky little rag, these are available in packs at your paint
supply store. You only need one.
Polishing Compounds
To get the
nice finish, you’re going to have to rub it out after its painted.
3M makes a nice set of compounds. You’ll need a quart bottle of 3M
rubbing compound, and a quart of “Perfect It II” finishing
compound.
Rubber Gloves
Get a good, heavy duty pair of rubber
gloves and use them anytime you’re working with the filler or the
paint products: the more you can keep off your hands, the better off
you’ll be.
Safety Goggles/Glasses
Any time you’re
working with power equipment, like an electric buffer, you’ll want
to protect your eyes.
Scotchbrite
Finally, you’ll need a
couple of sheets of Scotchbrite pads. Scotchbrite pads come in different
colors to designate the “grit” of the pad: red, green and
grey are the most common. Pick up two sheets of the grey
stuff.
Degreaser
Buy a gallon of PPG DX330 wax and grease
remover. You’ll use it throughout the refinishing
process.
Primer & Paint
Volumes of books have been written on
this subject, and you can buy them at any bookstore if you’d like to
become an expert. But for what we’re going to do in our garage,
we’ll keep it simple: we need a system that will be relatively easy
to apply, and something that will dry fast (so the dust and bugs
don’t get into it while it’s wet).
Here’s the
object:
1. We need to be able to “seal” the surface
we’re working on. Fact is, a lot of our cars have had some
questionable work done to them, and we don’t know exactly what
materials have been applied. We need to be able to seal up whatever is
already there to make sure it doesn’t adversely react with the new
materials & paints we will be applying. The sealer should also provide a
good adhesion base for the work we will be doing. Epoxies work well as
sealers.
2. We need a good, thick primer/surfacer that will go on
easily, dry quickly, fill minor defects, and be easily sandable to produce
a perfectly smooth surface. Catalyzed urethane primers fit this bill
perfectly.
3. We want a basecoat/clearcoat system for our topcoat.
Basecoat paints dry extremely fast; almost as fast as you spray them.
They can be applied fairly “dry.” This eliminates runs & sags,
and greatly reduces the amount of dust and bug defects in the finish. The
clearcoat that gets applied over the basecoat dries much slower, but any
defects in the clear can simply be sanded out and buffed to produce a
perfect finish.
Every body-guy has his favorite paint supplier.
The most popular ones are PPG, Dupont, and Sherwin Williams. Recently,
some good foreign suppliers have entered the US market, like Standox. All
of these suppliers produce excellent products, and I wouldn’t
hesitate to use any of them. At our Shop facility, we use the top-end
Standox products. For home use, I use PPG. Due to its general
availability, I’ll discuss the PPG products here. All of the other
manufacturers have similar product lines, so use what’s available to
you in your area.
1. Primer/Sealer
An outstanding product to
seal the underlaying surface, create excellent adhesion, and to provide
very good corrosion protection (in the case of steel substrates) is the
PPG “DP” series primer. This primer can be applied directly
to bare steel, aluminum or fiberglass. It is available in a variety of
colors, but I recommend staying with the light colors, either light grey
or white, to assure uniform coverage of your subsequent topcoat
color:
DP 40LF Grey-green
DP 48LF White
DP 50LF
Grey
DP 74LF Red-brown
DP 90LF Black
It’s mixed 2:1
with a catalyst, part number DP401LF (regular) or DP402LF (fast). I use
the fast 402 catalyst when working at home to keep the dust out of the
primer. It can be reduced down 25% with DT870 Reducer to provide a thin,
moisture-proof, sealing layer that gives you an excellent base to start
working on.
2. Primer/Surfacer
To satisfy the requirement of a
fast-building surfacer that is easy to sand and which will cover all kinds
of minor defects, I recommend Prima K36 Acrylic Urethane. This light grey
primer looks like eggnog with baby powder added to it: it’s pretty
thick, and when properly mixed and sprayed, it’s like spraying on a
thin coat of body filler. And that’s what we want: a nice layer of
sandable material to work with. The K36 is mixed in a ratio of 5:1:1 with
K201 hardener and the same DT870 reducer you used for the DP sealer
(amazing how the products all work together, huh?).
3.
Basecoat
The Basecoat is your color coat. Your paint supply store will
custom mix the color for you. The product line is called Deltron, or
“DBU,” and it gets mixed with a reactive reducer, DRR1170
(1170 is a fast-dry reducer, great for use in the garage. DRR1185 and
1195 are slower drying, and better suited for use in a paint booth). A
gallon of DBU, once reduced, is enough to paint a mid-sized car like a
Chevelle: it gets mixed 1 part color to 1-1/2 parts reducer, so you get a
lot of paint out of a little color. A quart will do the front clip on a
‘Vette.
4. Clearcoat
Again, a lot of products are
available, but for our home-use purposes, I would use the Concept 2021.
This is a urethane clear that dries very glossy and very hard, producing
excellent long-lasting results. It is mixed in a ratio of 4:1:1 with the
DT reducer and DCX61 hardener.
Technique
Now that we
have a list of all the tools, materials and products, it’s time to
do some work. So here’s the technique:
Paint
Stripping
There is seldom a need to strip a ‘Vette down to
“bare” glass or gelcoat. You need to remove oxidized,
flaking, and non-adhering paint, but you don’t need to go any
further of you’re using a good sealer (which we are).
Chemical Strippers
Never use “Aircraft Stripper” on
a ‘Vette. Remember the movie “Alien” when they cut the
Alien’s knuckle and the “blood” ate its way right
through the floor and didn’t stop going? That’s what Aircraft
Stripper will do to your FRP or SMC panels: you can’t get it to stop
“eating.” We once spent 2 days with a Hotsie, steamcleaning
and solvent wiping a ‘Vette that a customer had tried to
“strip,” before we were able to get the stuff to quit eating
away the body. There are other chemical products out there intended for
‘Vettes, but I’ve never trusted them enough to use
them.
Media Blasting
The other method of stripping that creates
lots of work for us at the shop is when a customer takes his ‘Vette
to a place and has it blasted. Even the plastic bead blasting and walnut
shell blasting will erode the surface of the FRP and SMC panels. This
creates lots of work to restore the surface to a smooth, paintable
condition. There are people out there who specialize in this and who can
get good results. I’ve just never seen one.
Sanding
Yup,
you guessed it, Vern. If you want sure-fire, good results, and you
don’t want to screw anything up, you’re gonna’ be
sanding. For rough, damaged, or filled areas, you can load up your
16″ file board with a sheet of 80-grit and block sand the area to
shape. For the rest of the car and panels, 150-grit works well to remove
paint oxidation and to blend and smooth minor defects.
Repair
Process
As an example, let’s assume we have a ‘Vette hood
with oxidized paint and a couple of chips and gouges. Here’s the
step-by-step fix:
Prep:
Wash the surface to be worked to get rid
of the “big chunks” of dirt and grime. Then wipe everything
down liberally with the DX330 wax and grease remover: you don’t
want to “grind in” surface contaminants with your sandpaper,
so you have to have a clean surface before you do any sanding. Also, if
you suspect that any silicone products, like “Armor All” or
“Son of a Gun” have been used anywhere near the car or on the
tires, you’ll want to wipe everything down with a good silicone
remover. If you don’t, your paint, when applied, will
“fish-eye” like crazy, no matter how much sanding you do to
the car. DX440 can be used as a one-step wax/grease/silicone
remover.
1. Load up your file board with a sheet of 150. Using a
criss-cross pattern, and a slightly sideways motion to the board, sand the
entire hood area down to remove all loose and oxidized paint. Sand and
rough up the gouge areas. While sanding like this, any other defects in
the hood will become very visible.
2. Seal the entire thing with
your DP epoxy primer/sealer. Set your air pressure to 40 – 60
pounds and give it a couple of coats to make sure you have it all sealed
up. This layer of epoxy will prevent your topcoat layers from adversely
reacting with anything that has been previously applied to the surface,
and provides adhesion to the base material. Your filler, applied next,
will stick like you won’t believe to the DP epoxy sealer, providing
a solid, long-lasting repair.
3. Use your 3M Short Strand Filler
to build up the damaged areas and allow it to set up. Once hardened, load
up your board with a piece of 80-grit and shape and blend the repaired
area into the rest of the curves. Smooth it out with 150.
4.
Give the repaired area, and any minor dings and imperfections, a coat of
your Evercoat Plasticworks filler. Rough shape it if you need to with the
80-grit, then finish smoothing, shaping, and blending with your 150.
Always use your board in a criss-cross action to completely blend in the
repaired area.
5. Mix up a batch of K36 primer/surfacer and give
the whole thing a couple of good, wet coats at about 60 pounds of
pressure. Let it dry overnight.
6. Shoot a “guide
coat” on the K36. A guide coat is a VERY light, splotchy coat of
contrasting color. You can use a can of black spraypaint, hold it well
away from the surface, and very quickly wave it back and forth just enough
to get a little black overspray onto the K36. I have some cheap, black
lacquer that I load up in my paint gun, and just quickly
“mist” onto the surface.
7. With a piece of 150 on
your board, lightly sand the surface. Again, work the board in a diagonal
motion, sliding it slightly sideways. Then reverse the action and
cross-hatch back the other way. You can even work the board completely
sideways first one way, then the other, until the guide coat is removed.
The guide coat, by its presence, will show you any low spots and other
defects that need more sanding. Once you have sanded enough to remove all
of the guide coat, you will have a perfectly smooth, uniform body panel
with no ripples or defects.
8. Shoot another coat of K36 onto the
whole thing, and guide coat it again. This process is called “block
and re-prime,” and is your assurance of very straight
panels.
9. What I now like to do is to load up a sheet of 220 on
my board and lightly go over the entire surface again, looking for any
defects and blocking down any significant high spots. I don’t
remove all of the guide coat: just enough to assure myself that there are
no defects and that the panel is smooth and straight. I then give this
surface a very light, fresh guide coat.
10. Get a bucket of warm
water and put a couple of drops of dish soap in it. The soap will act as
a lubricant as you sand, preventing your sandpaper from catching or
sticking to the surface being sanded. Also, it will give you soft, subtle
hands, so your wife and/or girlfriend will want you to touch her when
you’re all done sanding….(one of the few fringe benefits of
doing body work). Tear a few pieces of your 600-grit paper in half, and
let them soak in the water until they curl up. Then wrap a piece of 600
around your rubberized sanding block and sand the entire surface in long,
cross-hatching motions until all of the guide coat is gone. It takes some
time. Once completed, you’ll actually have a perfectly smooth,
near-gloss surface that’s smoother and flatter than the factory ever
made it.
11. Touch-up any areas where you have sanded through the
K36 with a little DP just to seal it up.
12. Hose down your garage
floor with a water hose. The wet floor will “capture” dust
and dirt in the air and will give you a better finish.
13. If the
K36 and/or DP has been on the car for a while, scuff it down good with
your grey Scotchbrite pad. This will open up the pores in the surface and
promote better adhesion of your color coat. Go over the entire surface
with your DX330 wax and grease remover.
14. After drying and
wiping down the surface, masking the car off, and going over it with a
tack cloth, mix and shoot your basecoat. Basecoat naturally goes on a
little dry, and it does not have a shine to it, so don’t succumb to
the temptation of laying it on too wet. After the first coat, wait about
20 minutes, then apply a second coat. After the second coat, I like to go
over the entire surface with light, diagonal, crosshatching coats. This
will eliminate any “tigerstripe” effects in your metallic
paint.
15. After 30 minutes, mix and apply your clear. I like to
lay on a slightly dry coat first, or a “tack coat.” Then put
down a nice wet layer, wait half an hour, and lay on a second wet layer.
If you get a little run, or some dust gets in it, don’t worry about
it.
16. Let it all dry for a day. Then throw a few sheets of
1500-grit into your warm water and soap bucket, wrap the 1500 around your
rubber pad, and wet-sand the clearcoat down to a smooth, defect-free
surface. This is known as “color sanding.” Stay away from
edges and raised features, as the clearcoat will be very thin in these
areas: you don’t want to sand through the clear. As the surface
dries, and you wipe it clean with a towel, you’ll be able to see the
areas that need more sanding to eliminate any “orange peel”
effect. With a bit of work, you can get the surface as smooth as a piece
of glass.
17. Rub the whole thing out with your electric polisher
and a foam rubber pad. Wear your safety goggles, because the rubbing
compound will really splatter around, including into your face. Also,
it’s a good idea to wear a protective apron of some sort to protect
your clothing, as the compounds will stain your clothes. Start with the
Rubbing Compound, and keep the polisher moving with long, smooth motions.
Rub until all of the dullness from the sanding is gone, and the surface
looks nearly like a mirror. Then switch over to the
“Perfect-It” finishing compound and do it again. When
you’re done, you’ll be able to see the second-hand on your
watch from 10 feet away in the reflection (no…you can’t do
this if you own a digital watch).