www.ModelAviation.com May 2012 Model Aviation 129
cl aerobatics
I was finishing a new CL Stunt model
for use at the 1969 Nats. I opted to use
a lacquer-based primer as a filler coat. It
went on great and sanded extremely well,
but after I had applied the dope color
coats and the trim colors, I applied several
coats of clear model airplane dope as a
top coat. The clear reacted with the auto
body filler coat and “bled” through the
colors, ruining the finish and effectively
keeping me from flying at that Nats. That
experience soured me on experimenting
with anything other than traditional
model finishes for many years.
In the interim, lacquer-based auto paint
systems have all but disappeared. The
new basecoat/clearcoat systems are more
volatile organic compound-compliant and
seem to be much easier to apply. Now I’m
using a basecoat/clearcoat system, and I
have no worries that the auto body-type
primer will bleed through the color coat
when the clear is applied.
Auto Primer
My friend, Lou Wolgast, is an
accomplished auto body technician, and
T The response to the discussions in this column about DuPont ChromaBase paints
and how to use them in painting CL Stunt models has been overwhelming. It
seems that many modelers have been contemplating the use of either basecoat/
clearcoat car paint systems, or water-based paint systems as a replacement or alternative
to the use of model airplane dope.
I’ve received correspondence from readers, many calls from friends about the subject,
questions about the paint, and stories from those who have been experimenting with it
for years. The consensus is that there are many paint systems out there that can be used
in place of dope for finishing our models. The correspondence also suggested to me that
there is a thirst for more detailed information on the subject.
I’ve had discussions with friends who are active in the automotive painting/collision
repair industry, which have convinced me that I’ve only scratched the surface of this.
The experiences I’ve had with the ChromaBase paints have been to use them over
traditional model airplane dope-based fillers and primers. I had not used any of the auto
body-type primers or fillers, in part because of a horrible experience that I had many
years ago.
Auto body paint systems
by Bob Hunt
[email protected]
Right: The Project Hole Shot model illustrates the steps in applying
the three-part auto primer and the ChromaBase silver blocking coat.
The silver completely covers the blotchy, sanded primer.
Right: The surface quality of the
burnished silver coat is evident. Using
the ChromaBase system is a fast, light,
and easy way to finish a model.
Buddy Wieder burnishes the surface of
the ChromaBase silver paint, breaking
its eggshell-like surface and allowing it
to better accept the final color coats.
an expert builder, finisher, and CL Stunt
pilot. He showed up at the Vintage Stunt
Championships (VSC) last year with a
version of his gorgeous, original-design
Fury that was resplendent in a high-gloss
red finish.
Lou and I spoke about that model and
it turns out that it was painted using the
DuPont ChromaBase basecoat/clearcoat
system. Lou also used the DuPont Nasson
primer. I asked him why he opted to use
that primer instead of a dope-based type
and he told me something that I had
not thought of: the multipart (primer/
activator/reducer) auto primers do not
shrink! That alone is reason enough to
use them. Dope-based primers shrink
over time and reveal grain and seams, and
even promote twisting of the airframe
components. Today’s multipart auto
primers do not!
Buddy Wieder and I went to the local
auto paint store that I mentioned in my
January column and asked my technician
friend, Dean Metzger, about the DuPont
primer. He suggested that we use the
store-brand primer, which he told us was
being used by virtually all of the local
body shops. Apparently this primer has all
the properties of the higher-priced types,
but at substantial savings.
Dean has not yet led me wrong, so
we took his advice and bought a gallon
of the proprietary three-part primer. It
was to be mixed as four parts primer to
one part activator to one-to-two parts
reducer. Dean told us that if we had a
well-prepared and flaw-free base that we
could use more reducer (up to two parts)
and achieve a more even flow out of the
product and obtain a thinner and lighter
result.
Dean was again on the money. Buddy
and I mixed 6 ounces of material and
painted my new Classic model, a Gene
Schaffer-designed Oosa-Amma. The
primer was applied using an inexpensive,
siphon-feed spray gun, and it went on
beautifully. The directions said to let it
cure for at least three hours, and we let it
sit for roughly six.
Sanding was done using #400-grit wet
or dry (silicon carbide) sandpaper and a
thin foam block. The foam block ensures
that the surface will be sanded evenly
with no finger pressure points and if, while
sanding, an adjacent part is inadvertently
hit, there will be no damage. The foam
block will crush and prevent any dings or
dents. I dry sanded the primer.
I sanded all the material I could off of
the airframe. The only primer left on the
model was that which filled the minor
imperfections in the model’s surface. For
those who have sanded talcum powder
and dope filler coat in the past, I’d say that
you will find the effort required to sand
the auto primer roughly the same.
Lou reminded me to mention that
if you are spraying the primer on over
an open-bay surface with ribs and cap
strips, be sure to thin the primer slightly
more and use much less on the covered
areas. If you spray a too-thick coat over
the open bay areas, you risk cutting the
covering at the edge of a rib or cap strip
with sandpaper as you remove the primer.
A thin coat of primer will fill in any open
weave on the silkspan or Polyspan and
will be much easier to sand.
Lou told me that you can usually
purchase the primer in one of several
colors. Use the color primer that is closest
to the actual base color with which you
will paint the airplane, making it easier for
the color to cover in fewer, thinner coats.
This presupposes that you will only sand
the surface of the primer smooth and not
actually sand through to the basecoats.
Lou said that there are tints available to
allow the user to custom make a primer
color that will be as close to the eventual
color coats as possible. Primer is heavy,
and I prefer to sand it all off, leaving only
the low spots filled.
I use 0.2-ounce carbon fiber to cover
my models and I fill that with several
coats of nonshrink airplane dope, sanding
between every other coat. The carbon is
black, and when the primer is sanded off
of the model, most of the surface remains
black. That can be difficult to cover with a
light color such as white or yellow.
Blocking Coat
In the past I sprayed on a thin
“blocking” coat consisting of Polar Gray
and white model airplane dope. This
blocking coat brings the model to a color
value that is nearly white and allows
fewer coats of white paint to be applied to
achieve the desired results.
The blocking coat also allows you to
inspect the model’s surface for any minor
132 Model Aviation May 2012 www.ModelAviation.com
imperfections. These imperfections can be
filled with spot putty, sanded smooth, and
have an additional blocking coat sprayed
on to achieve a constant color over the
entire model.
My new method is to use a coat of
ChromaBase silver paint as the blocking
coat instead of the dope-based blocking
coat. It makes sense to use auto paints
as soon as possible and stay with those
products to ensure that there will be no
incompatibility problems. Additionally,
the silver paint will show off minor
imperfections in the model’s surface even
better than the Polar Gray and white
dope mix.
As I mentioned in the past two “CL
Stunt” columns, ChromaBase paints will
harden to a shell-like surface finish after
approximately 48 hours; that surface
can then be burnished with a Scotch-
Brite Ultra Fine pad before applying any
additional color or trim. In the case of the
silver ChromaBase paint, it allows you
to achieve a virtually perfect surface on
which to paint because the silver blocks
out the blotchy surface of the sanded
primer/carbon fiber and also magnifies
any microscopic imperfections.
After applying the thin coat of silver
and then burnishing it, you will be able
to fix even the most minor imperfections
by using the edge of a single-edge razor
blade to apply spot putty into the areas
that need attention. You can then block
sand the glazing compound to match the
surface, and spot in more silver to regain
the one-color look.
Before trying it on a front-line model,
Buddy and I shot the Project Hole Shot
model with the auto body three-part
primer, sanded the top of one wing panel
thoroughly, and then shot a thin coat of
ChromaBase silver paint onto the outer
half of the primed and sanded panel.
We burnished the surface of the silver
with the Scotch-Brite pad. The next step
would be to apply the finish-color coat.
I have included a couple of pictures of
the sequence on the Hole Shot to show
just how simple, quick, and effective this
system is.
Step-by-Step Finishing Procedure
Several people have asked for a stepby-
step finishing procedure for the
ChromaBase and other basecoat/clearcoat
systems. Here’s what I’ve come up with
to this point for a typical foam-wingequipped
model. I’m certain that this
procedure will be tweaked in the months
and years to come, but I’m confident that
this sequence will yield impressive, light,
and quick results.
1. Finish-sand the model thoroughly using
#400 grit sandpaper and a foam block.
2. Apply two coats of Randolph Non-
Tautening butyrate dope.
3. Cover the model with 0.2-ounce-persquare-
yard carbon mat using 80% to 90%
thinned dope.
4. Sand the model’s surface smooth and
apply two coats of moderately thinned
butyrate dope.
5. Sand the surface smooth, apply two
more coats of dope, and then sand the
surface smooth one last time.
6. Apply a coat of three-part auto body
primer and let it cure.
7. Sand the primer off using #400 wet or
dry sandpaper and a foam block.
8. Apply a thin coat of ChromaBase
silver paint (I use the silver color coded
LM580K). Let this coat cure for 48 hours.
9. Burnish the surface of the silver using a
Scotch-Brite Ultra Fine pad (Part #37448).
10. Fill any minor imperfections using
3M Acryl-Green Spot Putty or a similar
product. Then block sand the putty
smooth. Recoat the putty-filled spot and
sanded areas with another thin coat of
silver then burnish those areas again with
the Scotch-Brite pad.
11. Spray on the basecoat color using
ChromaBase paint.
12. After 48 hours, you can burnish the
surface of the color with the Scotch-Brite
pad.
13. Apply trim and any surface detailing
(decals, vinyl appliqués, etc.).
14. Shoot on a coat of DuPont
ChromaClear (I prefer the G2-7779S
Multi-Mix clear) or a similar two-part
automotive clear.
15. Let the clear cure overnight, then
sand the surface dull using 2,000-grit
sandpaper and soapy water.
16. Buff the model using a fine
compound.
A few final cautions are in order. Be
sure to use only original-formula (blue)
Windex as a cleaner before using any of
the above listed products. Follow all of the
safety precautions when using any type
of catalyzed paints such as the three-part
primer and the ChromaBase clears.
I’ll report on new finishing procedures
and products as they become known and
proven. Next time we’ll get back to some
other aspects of building and flying CL
Stunt models.
Till then, fly Stunt!
Sources :
DuPont ChromaSystems Paints
http://bit.ly/omdzpr
3M/Scotch-Brite
(888) 364-3577
www.3m.com
Precision Aerobatics Model Pilots Association
www.control-line.org
cl aerobatics
Specializing in 26cc &
Larger Civilian Scale ARFsLarger ARFs
All our ARF's are laser cut balsa and
plywood. Fiberglass cowls and some
with fi berglass bodies.
Complete hardware kits.
www.TexasRCPlanes.com
936-829-2477 • 200 Judd St., Diboll Texas 75941
Edition: Model Aviation - 2012/05
Page Numbers: 129,131,132
Edition: Model Aviation - 2012/05
Page Numbers: 129,131,132
www.ModelAviation.com May 2012 Model Aviation 129
cl aerobatics
I was finishing a new CL Stunt model
for use at the 1969 Nats. I opted to use
a lacquer-based primer as a filler coat. It
went on great and sanded extremely well,
but after I had applied the dope color
coats and the trim colors, I applied several
coats of clear model airplane dope as a
top coat. The clear reacted with the auto
body filler coat and “bled” through the
colors, ruining the finish and effectively
keeping me from flying at that Nats. That
experience soured me on experimenting
with anything other than traditional
model finishes for many years.
In the interim, lacquer-based auto paint
systems have all but disappeared. The
new basecoat/clearcoat systems are more
volatile organic compound-compliant and
seem to be much easier to apply. Now I’m
using a basecoat/clearcoat system, and I
have no worries that the auto body-type
primer will bleed through the color coat
when the clear is applied.
Auto Primer
My friend, Lou Wolgast, is an
accomplished auto body technician, and
T The response to the discussions in this column about DuPont ChromaBase paints
and how to use them in painting CL Stunt models has been overwhelming. It
seems that many modelers have been contemplating the use of either basecoat/
clearcoat car paint systems, or water-based paint systems as a replacement or alternative
to the use of model airplane dope.
I’ve received correspondence from readers, many calls from friends about the subject,
questions about the paint, and stories from those who have been experimenting with it
for years. The consensus is that there are many paint systems out there that can be used
in place of dope for finishing our models. The correspondence also suggested to me that
there is a thirst for more detailed information on the subject.
I’ve had discussions with friends who are active in the automotive painting/collision
repair industry, which have convinced me that I’ve only scratched the surface of this.
The experiences I’ve had with the ChromaBase paints have been to use them over
traditional model airplane dope-based fillers and primers. I had not used any of the auto
body-type primers or fillers, in part because of a horrible experience that I had many
years ago.
Auto body paint systems
by Bob Hunt
[email protected]
Right: The Project Hole Shot model illustrates the steps in applying
the three-part auto primer and the ChromaBase silver blocking coat.
The silver completely covers the blotchy, sanded primer.
Right: The surface quality of the
burnished silver coat is evident. Using
the ChromaBase system is a fast, light,
and easy way to finish a model.
Buddy Wieder burnishes the surface of
the ChromaBase silver paint, breaking
its eggshell-like surface and allowing it
to better accept the final color coats.
an expert builder, finisher, and CL Stunt
pilot. He showed up at the Vintage Stunt
Championships (VSC) last year with a
version of his gorgeous, original-design
Fury that was resplendent in a high-gloss
red finish.
Lou and I spoke about that model and
it turns out that it was painted using the
DuPont ChromaBase basecoat/clearcoat
system. Lou also used the DuPont Nasson
primer. I asked him why he opted to use
that primer instead of a dope-based type
and he told me something that I had
not thought of: the multipart (primer/
activator/reducer) auto primers do not
shrink! That alone is reason enough to
use them. Dope-based primers shrink
over time and reveal grain and seams, and
even promote twisting of the airframe
components. Today’s multipart auto
primers do not!
Buddy Wieder and I went to the local
auto paint store that I mentioned in my
January column and asked my technician
friend, Dean Metzger, about the DuPont
primer. He suggested that we use the
store-brand primer, which he told us was
being used by virtually all of the local
body shops. Apparently this primer has all
the properties of the higher-priced types,
but at substantial savings.
Dean has not yet led me wrong, so
we took his advice and bought a gallon
of the proprietary three-part primer. It
was to be mixed as four parts primer to
one part activator to one-to-two parts
reducer. Dean told us that if we had a
well-prepared and flaw-free base that we
could use more reducer (up to two parts)
and achieve a more even flow out of the
product and obtain a thinner and lighter
result.
Dean was again on the money. Buddy
and I mixed 6 ounces of material and
painted my new Classic model, a Gene
Schaffer-designed Oosa-Amma. The
primer was applied using an inexpensive,
siphon-feed spray gun, and it went on
beautifully. The directions said to let it
cure for at least three hours, and we let it
sit for roughly six.
Sanding was done using #400-grit wet
or dry (silicon carbide) sandpaper and a
thin foam block. The foam block ensures
that the surface will be sanded evenly
with no finger pressure points and if, while
sanding, an adjacent part is inadvertently
hit, there will be no damage. The foam
block will crush and prevent any dings or
dents. I dry sanded the primer.
I sanded all the material I could off of
the airframe. The only primer left on the
model was that which filled the minor
imperfections in the model’s surface. For
those who have sanded talcum powder
and dope filler coat in the past, I’d say that
you will find the effort required to sand
the auto primer roughly the same.
Lou reminded me to mention that
if you are spraying the primer on over
an open-bay surface with ribs and cap
strips, be sure to thin the primer slightly
more and use much less on the covered
areas. If you spray a too-thick coat over
the open bay areas, you risk cutting the
covering at the edge of a rib or cap strip
with sandpaper as you remove the primer.
A thin coat of primer will fill in any open
weave on the silkspan or Polyspan and
will be much easier to sand.
Lou told me that you can usually
purchase the primer in one of several
colors. Use the color primer that is closest
to the actual base color with which you
will paint the airplane, making it easier for
the color to cover in fewer, thinner coats.
This presupposes that you will only sand
the surface of the primer smooth and not
actually sand through to the basecoats.
Lou said that there are tints available to
allow the user to custom make a primer
color that will be as close to the eventual
color coats as possible. Primer is heavy,
and I prefer to sand it all off, leaving only
the low spots filled.
I use 0.2-ounce carbon fiber to cover
my models and I fill that with several
coats of nonshrink airplane dope, sanding
between every other coat. The carbon is
black, and when the primer is sanded off
of the model, most of the surface remains
black. That can be difficult to cover with a
light color such as white or yellow.
Blocking Coat
In the past I sprayed on a thin
“blocking” coat consisting of Polar Gray
and white model airplane dope. This
blocking coat brings the model to a color
value that is nearly white and allows
fewer coats of white paint to be applied to
achieve the desired results.
The blocking coat also allows you to
inspect the model’s surface for any minor
132 Model Aviation May 2012 www.ModelAviation.com
imperfections. These imperfections can be
filled with spot putty, sanded smooth, and
have an additional blocking coat sprayed
on to achieve a constant color over the
entire model.
My new method is to use a coat of
ChromaBase silver paint as the blocking
coat instead of the dope-based blocking
coat. It makes sense to use auto paints
as soon as possible and stay with those
products to ensure that there will be no
incompatibility problems. Additionally,
the silver paint will show off minor
imperfections in the model’s surface even
better than the Polar Gray and white
dope mix.
As I mentioned in the past two “CL
Stunt” columns, ChromaBase paints will
harden to a shell-like surface finish after
approximately 48 hours; that surface
can then be burnished with a Scotch-
Brite Ultra Fine pad before applying any
additional color or trim. In the case of the
silver ChromaBase paint, it allows you
to achieve a virtually perfect surface on
which to paint because the silver blocks
out the blotchy surface of the sanded
primer/carbon fiber and also magnifies
any microscopic imperfections.
After applying the thin coat of silver
and then burnishing it, you will be able
to fix even the most minor imperfections
by using the edge of a single-edge razor
blade to apply spot putty into the areas
that need attention. You can then block
sand the glazing compound to match the
surface, and spot in more silver to regain
the one-color look.
Before trying it on a front-line model,
Buddy and I shot the Project Hole Shot
model with the auto body three-part
primer, sanded the top of one wing panel
thoroughly, and then shot a thin coat of
ChromaBase silver paint onto the outer
half of the primed and sanded panel.
We burnished the surface of the silver
with the Scotch-Brite pad. The next step
would be to apply the finish-color coat.
I have included a couple of pictures of
the sequence on the Hole Shot to show
just how simple, quick, and effective this
system is.
Step-by-Step Finishing Procedure
Several people have asked for a stepby-
step finishing procedure for the
ChromaBase and other basecoat/clearcoat
systems. Here’s what I’ve come up with
to this point for a typical foam-wingequipped
model. I’m certain that this
procedure will be tweaked in the months
and years to come, but I’m confident that
this sequence will yield impressive, light,
and quick results.
1. Finish-sand the model thoroughly using
#400 grit sandpaper and a foam block.
2. Apply two coats of Randolph Non-
Tautening butyrate dope.
3. Cover the model with 0.2-ounce-persquare-
yard carbon mat using 80% to 90%
thinned dope.
4. Sand the model’s surface smooth and
apply two coats of moderately thinned
butyrate dope.
5. Sand the surface smooth, apply two
more coats of dope, and then sand the
surface smooth one last time.
6. Apply a coat of three-part auto body
primer and let it cure.
7. Sand the primer off using #400 wet or
dry sandpaper and a foam block.
8. Apply a thin coat of ChromaBase
silver paint (I use the silver color coded
LM580K). Let this coat cure for 48 hours.
9. Burnish the surface of the silver using a
Scotch-Brite Ultra Fine pad (Part #37448).
10. Fill any minor imperfections using
3M Acryl-Green Spot Putty or a similar
product. Then block sand the putty
smooth. Recoat the putty-filled spot and
sanded areas with another thin coat of
silver then burnish those areas again with
the Scotch-Brite pad.
11. Spray on the basecoat color using
ChromaBase paint.
12. After 48 hours, you can burnish the
surface of the color with the Scotch-Brite
pad.
13. Apply trim and any surface detailing
(decals, vinyl appliqués, etc.).
14. Shoot on a coat of DuPont
ChromaClear (I prefer the G2-7779S
Multi-Mix clear) or a similar two-part
automotive clear.
15. Let the clear cure overnight, then
sand the surface dull using 2,000-grit
sandpaper and soapy water.
16. Buff the model using a fine
compound.
A few final cautions are in order. Be
sure to use only original-formula (blue)
Windex as a cleaner before using any of
the above listed products. Follow all of the
safety precautions when using any type
of catalyzed paints such as the three-part
primer and the ChromaBase clears.
I’ll report on new finishing procedures
and products as they become known and
proven. Next time we’ll get back to some
other aspects of building and flying CL
Stunt models.
Till then, fly Stunt!
Sources :
DuPont ChromaSystems Paints
http://bit.ly/omdzpr
3M/Scotch-Brite
(888) 364-3577
www.3m.com
Precision Aerobatics Model Pilots Association
www.control-line.org
cl aerobatics
Specializing in 26cc &
Larger Civilian Scale ARFsLarger ARFs
All our ARF's are laser cut balsa and
plywood. Fiberglass cowls and some
with fi berglass bodies.
Complete hardware kits.
www.TexasRCPlanes.com
936-829-2477 • 200 Judd St., Diboll Texas 75941
Edition: Model Aviation - 2012/05
Page Numbers: 129,131,132
www.ModelAviation.com May 2012 Model Aviation 129
cl aerobatics
I was finishing a new CL Stunt model
for use at the 1969 Nats. I opted to use
a lacquer-based primer as a filler coat. It
went on great and sanded extremely well,
but after I had applied the dope color
coats and the trim colors, I applied several
coats of clear model airplane dope as a
top coat. The clear reacted with the auto
body filler coat and “bled” through the
colors, ruining the finish and effectively
keeping me from flying at that Nats. That
experience soured me on experimenting
with anything other than traditional
model finishes for many years.
In the interim, lacquer-based auto paint
systems have all but disappeared. The
new basecoat/clearcoat systems are more
volatile organic compound-compliant and
seem to be much easier to apply. Now I’m
using a basecoat/clearcoat system, and I
have no worries that the auto body-type
primer will bleed through the color coat
when the clear is applied.
Auto Primer
My friend, Lou Wolgast, is an
accomplished auto body technician, and
T The response to the discussions in this column about DuPont ChromaBase paints
and how to use them in painting CL Stunt models has been overwhelming. It
seems that many modelers have been contemplating the use of either basecoat/
clearcoat car paint systems, or water-based paint systems as a replacement or alternative
to the use of model airplane dope.
I’ve received correspondence from readers, many calls from friends about the subject,
questions about the paint, and stories from those who have been experimenting with it
for years. The consensus is that there are many paint systems out there that can be used
in place of dope for finishing our models. The correspondence also suggested to me that
there is a thirst for more detailed information on the subject.
I’ve had discussions with friends who are active in the automotive painting/collision
repair industry, which have convinced me that I’ve only scratched the surface of this.
The experiences I’ve had with the ChromaBase paints have been to use them over
traditional model airplane dope-based fillers and primers. I had not used any of the auto
body-type primers or fillers, in part because of a horrible experience that I had many
years ago.
Auto body paint systems
by Bob Hunt
[email protected]
Right: The Project Hole Shot model illustrates the steps in applying
the three-part auto primer and the ChromaBase silver blocking coat.
The silver completely covers the blotchy, sanded primer.
Right: The surface quality of the
burnished silver coat is evident. Using
the ChromaBase system is a fast, light,
and easy way to finish a model.
Buddy Wieder burnishes the surface of
the ChromaBase silver paint, breaking
its eggshell-like surface and allowing it
to better accept the final color coats.
an expert builder, finisher, and CL Stunt
pilot. He showed up at the Vintage Stunt
Championships (VSC) last year with a
version of his gorgeous, original-design
Fury that was resplendent in a high-gloss
red finish.
Lou and I spoke about that model and
it turns out that it was painted using the
DuPont ChromaBase basecoat/clearcoat
system. Lou also used the DuPont Nasson
primer. I asked him why he opted to use
that primer instead of a dope-based type
and he told me something that I had
not thought of: the multipart (primer/
activator/reducer) auto primers do not
shrink! That alone is reason enough to
use them. Dope-based primers shrink
over time and reveal grain and seams, and
even promote twisting of the airframe
components. Today’s multipart auto
primers do not!
Buddy Wieder and I went to the local
auto paint store that I mentioned in my
January column and asked my technician
friend, Dean Metzger, about the DuPont
primer. He suggested that we use the
store-brand primer, which he told us was
being used by virtually all of the local
body shops. Apparently this primer has all
the properties of the higher-priced types,
but at substantial savings.
Dean has not yet led me wrong, so
we took his advice and bought a gallon
of the proprietary three-part primer. It
was to be mixed as four parts primer to
one part activator to one-to-two parts
reducer. Dean told us that if we had a
well-prepared and flaw-free base that we
could use more reducer (up to two parts)
and achieve a more even flow out of the
product and obtain a thinner and lighter
result.
Dean was again on the money. Buddy
and I mixed 6 ounces of material and
painted my new Classic model, a Gene
Schaffer-designed Oosa-Amma. The
primer was applied using an inexpensive,
siphon-feed spray gun, and it went on
beautifully. The directions said to let it
cure for at least three hours, and we let it
sit for roughly six.
Sanding was done using #400-grit wet
or dry (silicon carbide) sandpaper and a
thin foam block. The foam block ensures
that the surface will be sanded evenly
with no finger pressure points and if, while
sanding, an adjacent part is inadvertently
hit, there will be no damage. The foam
block will crush and prevent any dings or
dents. I dry sanded the primer.
I sanded all the material I could off of
the airframe. The only primer left on the
model was that which filled the minor
imperfections in the model’s surface. For
those who have sanded talcum powder
and dope filler coat in the past, I’d say that
you will find the effort required to sand
the auto primer roughly the same.
Lou reminded me to mention that
if you are spraying the primer on over
an open-bay surface with ribs and cap
strips, be sure to thin the primer slightly
more and use much less on the covered
areas. If you spray a too-thick coat over
the open bay areas, you risk cutting the
covering at the edge of a rib or cap strip
with sandpaper as you remove the primer.
A thin coat of primer will fill in any open
weave on the silkspan or Polyspan and
will be much easier to sand.
Lou told me that you can usually
purchase the primer in one of several
colors. Use the color primer that is closest
to the actual base color with which you
will paint the airplane, making it easier for
the color to cover in fewer, thinner coats.
This presupposes that you will only sand
the surface of the primer smooth and not
actually sand through to the basecoats.
Lou said that there are tints available to
allow the user to custom make a primer
color that will be as close to the eventual
color coats as possible. Primer is heavy,
and I prefer to sand it all off, leaving only
the low spots filled.
I use 0.2-ounce carbon fiber to cover
my models and I fill that with several
coats of nonshrink airplane dope, sanding
between every other coat. The carbon is
black, and when the primer is sanded off
of the model, most of the surface remains
black. That can be difficult to cover with a
light color such as white or yellow.
Blocking Coat
In the past I sprayed on a thin
“blocking” coat consisting of Polar Gray
and white model airplane dope. This
blocking coat brings the model to a color
value that is nearly white and allows
fewer coats of white paint to be applied to
achieve the desired results.
The blocking coat also allows you to
inspect the model’s surface for any minor
132 Model Aviation May 2012 www.ModelAviation.com
imperfections. These imperfections can be
filled with spot putty, sanded smooth, and
have an additional blocking coat sprayed
on to achieve a constant color over the
entire model.
My new method is to use a coat of
ChromaBase silver paint as the blocking
coat instead of the dope-based blocking
coat. It makes sense to use auto paints
as soon as possible and stay with those
products to ensure that there will be no
incompatibility problems. Additionally,
the silver paint will show off minor
imperfections in the model’s surface even
better than the Polar Gray and white
dope mix.
As I mentioned in the past two “CL
Stunt” columns, ChromaBase paints will
harden to a shell-like surface finish after
approximately 48 hours; that surface
can then be burnished with a Scotch-
Brite Ultra Fine pad before applying any
additional color or trim. In the case of the
silver ChromaBase paint, it allows you
to achieve a virtually perfect surface on
which to paint because the silver blocks
out the blotchy surface of the sanded
primer/carbon fiber and also magnifies
any microscopic imperfections.
After applying the thin coat of silver
and then burnishing it, you will be able
to fix even the most minor imperfections
by using the edge of a single-edge razor
blade to apply spot putty into the areas
that need attention. You can then block
sand the glazing compound to match the
surface, and spot in more silver to regain
the one-color look.
Before trying it on a front-line model,
Buddy and I shot the Project Hole Shot
model with the auto body three-part
primer, sanded the top of one wing panel
thoroughly, and then shot a thin coat of
ChromaBase silver paint onto the outer
half of the primed and sanded panel.
We burnished the surface of the silver
with the Scotch-Brite pad. The next step
would be to apply the finish-color coat.
I have included a couple of pictures of
the sequence on the Hole Shot to show
just how simple, quick, and effective this
system is.
Step-by-Step Finishing Procedure
Several people have asked for a stepby-
step finishing procedure for the
ChromaBase and other basecoat/clearcoat
systems. Here’s what I’ve come up with
to this point for a typical foam-wingequipped
model. I’m certain that this
procedure will be tweaked in the months
and years to come, but I’m confident that
this sequence will yield impressive, light,
and quick results.
1. Finish-sand the model thoroughly using
#400 grit sandpaper and a foam block.
2. Apply two coats of Randolph Non-
Tautening butyrate dope.
3. Cover the model with 0.2-ounce-persquare-
yard carbon mat using 80% to 90%
thinned dope.
4. Sand the model’s surface smooth and
apply two coats of moderately thinned
butyrate dope.
5. Sand the surface smooth, apply two
more coats of dope, and then sand the
surface smooth one last time.
6. Apply a coat of three-part auto body
primer and let it cure.
7. Sand the primer off using #400 wet or
dry sandpaper and a foam block.
8. Apply a thin coat of ChromaBase
silver paint (I use the silver color coded
LM580K). Let this coat cure for 48 hours.
9. Burnish the surface of the silver using a
Scotch-Brite Ultra Fine pad (Part #37448).
10. Fill any minor imperfections using
3M Acryl-Green Spot Putty or a similar
product. Then block sand the putty
smooth. Recoat the putty-filled spot and
sanded areas with another thin coat of
silver then burnish those areas again with
the Scotch-Brite pad.
11. Spray on the basecoat color using
ChromaBase paint.
12. After 48 hours, you can burnish the
surface of the color with the Scotch-Brite
pad.
13. Apply trim and any surface detailing
(decals, vinyl appliqués, etc.).
14. Shoot on a coat of DuPont
ChromaClear (I prefer the G2-7779S
Multi-Mix clear) or a similar two-part
automotive clear.
15. Let the clear cure overnight, then
sand the surface dull using 2,000-grit
sandpaper and soapy water.
16. Buff the model using a fine
compound.
A few final cautions are in order. Be
sure to use only original-formula (blue)
Windex as a cleaner before using any of
the above listed products. Follow all of the
safety precautions when using any type
of catalyzed paints such as the three-part
primer and the ChromaBase clears.
I’ll report on new finishing procedures
and products as they become known and
proven. Next time we’ll get back to some
other aspects of building and flying CL
Stunt models.
Till then, fly Stunt!
Sources :
DuPont ChromaSystems Paints
http://bit.ly/omdzpr
3M/Scotch-Brite
(888) 364-3577
www.3m.com
Precision Aerobatics Model Pilots Association
www.control-line.org
cl aerobatics
Specializing in 26cc &
Larger Civilian Scale ARFsLarger ARFs
All our ARF's are laser cut balsa and
plywood. Fiberglass cowls and some
with fi berglass bodies.
Complete hardware kits.
www.TexasRCPlanes.com
936-829-2477 • 200 Judd St., Diboll Texas 75941
