Scalecraft & Finish
1963 American Modeler
you are a beginner looking for advice on how to tackle a good old-fashioned
dope finish on your model, this article from the March-April edition
of American Modeler is about as fundamental as it get. The author
recommends methods for operating and cleaning a spray gun, how to
properly prepare a model for painting, taping off trim lines, and
even achieving that high gloss finish that so many contest grade
models have. If you are looking for pictures, then this article
is not for you - it's all business. However, if a picture is worth
a thousand words, then the inverse must be true that a thousand
words is worth a picture. That being so, this article contains three
Scalecraft & Finish
By Paul Plecan
You want your next scale job to be slicker,
smoother, and shinier, right? It takes patience and requires effort.
In this review we will cover Ukie, R/C and F/F in
that order. Since control-line weight is not an overwhelming consideration,
we can duplicate the "average" finish seen at most contests. Most
of us may be familiar with the amateur approach - too many coats
of dope too hastily applied, insufficient drying time and improper
sanding between. Yes, there is much more of an art to "sandpapering"
than meets the eye. It quite often is the hardest skill to master.
For the usual glow-plug equipped model, we need a
fuel-proof type undercoating and pigmented dope. Naturally, there
are favorites, but this is a personal thing. What works best for
you can only be determined by Y-O-U.
Some brands can
be mixed, but formulas frequently vary and mixing of two brands
can result in a useless goo. So test first before trying unknown
combos on a model. The beginner should go the whole route with a
single brand. Only deviation we make from the one-brand rule is
to use inexpensive thinner for cleaning hands after working with
dope or lacquer. While cheap thinner will do for this do not use
it with the undercoating or pigmented dope.
the dope to the model, we need brushes. Camel-hair, ox-hair, and
sable brushes are long-time favorites - you will get the quality
you pay for. Cheap brushes shed bristles and soon come apart entirely.
A wider brush will speed up work; 1/2" wide brushes are the minimum
to consider, 3/4" and 1" widths are popular. At least four brushes
are needed: one for undercoating, the others for light, medium,
and dark work (you discover that a brush, once used with black,
can not do much of a white dope job). Between two and three dollars
is needed for the four brushes, so take care of them.
Never, never allow dope to dry on a brush. Any time you must lay
it down, dip it in thinner and lightly squeeze out the dope. A handy
way to clean brushes is to have three small (approx. 1-oz) jars
lined up, 2/3 full of thinner. Dip the brush in #1, squeeze dry
with clean rag, repeat dip-dry sequence with #2 and #3. Keep jars
lightly covered, replenish thinner when dirty. Tighten caps when
not in use to keep thinner from evaporating. To get quality brushes
you may have to go to an art supply store.
method for applying dope is with a spray gun. A unit rated at a
minimum of 3 cubic feet of air per minute is required. Forty or
fifty dollars for a new outfit.
Happily, there is
an economical alternative in the spraying department. You can get
spray cans that are easy to use, or attachments that have separate
air pressure cans and dope jars. The latter allow custom-mixing
For two to three dollars, you get a head
assembly, a 4-oz jar, and a 15-oz pressure unit (extra pressure
units are between one and two dollars). Each pressure unit can spread
almost a quart of dope. It will pay you to have separate units for
light and dark work, maybe a third unit for intermediate shades.
The reason? It takes a fair bit of thinner through the sprayer to
clear out the previous color. Two or three "rinsings" to go from
a black to white for instance. There are instructions on the label
- read and follow them! When liquid in any integral spray can unit
is depleted, always release remaining gas pressure.
item on the shopping list is sandpaper. "Bargain basement" paper
will not do. At least 6 sheets each of 260 grit and 320 grit waterproof
sandpaper. You may find grit designation will vary - 280 and 400
grit is just as good as grades listed above. If sheet size is about
9" x 11", it will be much handier if these are cut into quarters
Let's assume your model is fully assembled, all
fabric or tissue surfaces having been water-sprayed and dried to
tighten up covering. Before we start with the undercoating, clear
dope all fabric or tissue areas. Undercoating directly on fabric
would overly increase weight.
You apply undercoating with
a brush or smooth it out with your fingertips, making it sink into
the pores of the balsa. This is our main objective - to fill in
Allow the first coat 30 minutes to dry, then
very lightly skimming the surface, sandpaper away the major imperfections.
This first sanding can be done with plain sandpaper of garnet type,
no rougher than 220 grit or 6/0. Your thumb and forefinger keep
the paper from slipping away, the pressure on the work being exerted
by the four finger tips. Lightly, now. Best motion pattern is circular
or elliptical. This eliminates the sudden stops of back and forth
straight motion, where the sandpaper digs in at the ends of the
stroke. Develop an even pressure and never linger in one spot -
idea is to remove an equal amount of undercoating all over the model.
In case anyone is confused, the term "undercoat" here means
any of the items known as primer surfacer, primer sealer, sanding
sealer or balsa fillercoat. A second coat of undercoating applied
is allowed 40 minutes to dry before sanding. Use the 260/280 grit
waterproof paper from now on - whether you dip it in water or use
it dry is not too important. Damp or wet usage is preferred. With
the application of the third coat of undercoating, it is a good
rule to allow even more drying time ... 50 minutes or more is a
necessity. From this point on, use the paper thoroughly wet. A dish
partly filled with water should be near at hand. Dip the paper into
it as soon as you feel it "drag" when sanding. You, should find
the balsa-dust and talc floating away from the paper each time you
dip it in the water. If it tends to clog up and lose its "bite,"
then the finish has not been allowed sufficient time to dry. Butyrate
type dope seems to take longer to dry thoroughly and tends to clog
the sandpaper quicker, but remains more flexible, even over a long
period of time, resulting in less "crazing" or splitting. This probably
is due to the use of more plasticizer (castor oil, etc.) in the
The sanding of the third coat should continue
until you can see that most of the surface coating has been removed
and you are sanding the model again. But there will be a great difference
now - if you hold the model near a strong light and look lengthwise
at any area, its surfaces should be quite slick. There is a chance
that the pores of the wood can still be detected. If a top-grade
finish is desired, another coat is called for (plus sanding).
When "three or four" coats of undercoating are specified
for a particular airplane, we must remember the biggest "variable"
of all is the model-builder. One reads the can labels, shakes and
stirs the solution well. Another just zips along, paying slight
attention to article, label, or well-meaning friends. This is the
guy who needs the extra coat. Maybe more, if he applies it with
a skimpy type technique.
By this time you should be
some sort of judge on drying times, sandpaper pressure, number of
coats. And your handiwork should reflect more truth when the word
"workmanship" is bandied about. Use of waterproof sandpaper should
not mean that the model stays wet continually. Once sanded, wipe
dry with a cloth or crumpled tissue. And even though dope tends
to sink in (undercoating, too) when the first few coats are applied,
you can sand too deep. If you do, this may let a bit of water penetrate
under the doped surface. You'll know when it happens, as just a
little water in the balsa wood will cause a blister or puffing up
to occur right where the water seeps through. Once this happens,
there is almost nothing one can do to correct it in a hurry. A series
of punctures with a very sharp X-actro blade or pin in the vicinity
of the blister will aid in letting the moisture escape, as will
leaving the model in any well-heated dry area. About a foot away
from a furnace, or even farther away if placed near a stove. Check
the damage within 20 minutes, as you may place the model too close
and the finish may blister from heat. Safer to let it dry overnight,
not too close to any very hot surface.
You should have a
model now that looks great even without color. But the pigments
are what we are after in any paint job. Before you proceed with
the color dope here's a tip for the "all-out" slick finish fans.
To be doubly sure of smooth surfaces, a coat of silver dope at this
point will reveal all the dimples, low points, slight pore effect
or other blemishes. Nothing else will more critically highlight
the slightest imperfections ... unless you want to use a microscope!
On with the colors. Always apply colored dope in smooth strokes
of the brush, flowing the liquid on with a minimum of "stroking."
This minimizes streaking and gives more even coverage. Keep a well-thought-out
program in mind; start with nose, left side, then right side of
fuselage. Top left wing panel, then bottom. Repeat for right wing.
Repeat wing sequence for horizontal tail surfaces. Left, then right
sides of rudder; lay aside to dry. Somewhere along the way now you
will realize that each succeeding coat of dope traps all the rest
under it. If any previous phase was rushed through, the dope remains
"wet" in actual truth even overnight. It is for this reason that
overnight drying is desired. The sanding goes that much easier,
and less clogging takes place too. You can almost pose as an expert
Certain colors have more "body" and hiding power than
others. Well-mixed black dope will cover most any previous color
in two coats. White takes more than six coats to effectively cover
black. So it depends on the particular color scheme as to how many
coats are required. If you choose a model with a light-colored paint
job, you will find that it takes four coats of light yellow or white
to achieve a solid body of color, without faint streaks or blotches.
Dark stripes or other trim should effectively cover the light areas
with two coats - three at most. If you aren't getting effective
coverage, you've let the dope settle too long after stirring or
shaking. You'll hardly ever need to change brands, as a poor paint
job reflects mostly the model-builder's lack of "know-how" more
than the quality of the dope used. There is a limit as to how much
you can learn by the "book" - you just have to get your hands dirty.
Which brings us to a minor matter - clothing. Cultivate
the habit of wearing your old tattered shirts and slacks when painting.
It only takes a drop or two to mess up some of your favorite threads.
And getting the pigment entirely out is only a matter of opinion
(you'll wind up with some sort of spot in any event). We don't usually
notice the spot until the dope has dried to some extent - it's too
late then. Shoes can be a problem too, but if you keep them shined,
the wax generally keeps the dope from actually getting into the
leather. Note that we said "generally."
light colors go on first. With white, six coats are needed. Most
other light colors. four coats. Dark covering coats, three. In extreme
cases; you could add two additional coats to each of above.
The use of rubbing compounds is recommended on the "museum piece,"
U-control stunt or scale or an R/C model that you have invested
in heavily, money-wise. Along with the rubbing compound, you'll
want to use gloss wax. Read the instructions on the can and use
plenty of elbow-grease.
After flying, the sooner you clean
your model, and the less time you leave spilled fuel on your model,
the better. Pactra's Plane Kleener or rubbing alcohol will cut into
the exhaust sludge that streaks the engine cowl and the bottom of
the fuselage. Store models in an unheated area of the house, as
the average "indoor" portion of most houses is too dry, causing
the finish to "craze" in short irregular cracks that generally cover
the entire model. With the passage of time, cracks sometimes enlarge
so the darker areas split enough for the lighter coats to be seen.
This condition can be prevented on your next painting job
by adding a drop of castor oil to each ounce of dope that is used.
Castor oil slows down the drying of the dope, calling for a longer
wait before sanding. With even an overnight drying period. you will
find the sandpaper loading up more more quickly (so you will need
about double the usual requirements).
who uses a spray gun should follow manufacturer's instructions -
and always keep the gun in motion. Maintain an even rate of rotary
motion for even coverage, working at a constant distance from the
painted surface. You soon learn the vital importance of snug masking
and air-tight "cocooning" of lighter areas when working with dark
colors. The merest hole will allow some of the darker mist to penetrate
to mess up the job.
Unless you have a large work area that
is both heated and well ventilated, forget spraying. A warm area
(65 to 70°) is needed to get proper atomization and ventilation
(through-wall fan duct) is needed to carry off fumes. Without proper
ventilation, an average spray session will leave droplets all over
you and everything in the spray room. An open door to the rest of
the house will mean a dope-mist on drapes and furniture. Always
have all the preparatory work finished before loading your spray
gun. You don't want the pigments to settle before you get into action.
By loading and being ready to spray, you get those pigment particles
onto the model, where they belong.
For R/C .models, the
same general instructions apply. Do not overload such planes with
too much pigmented dope. You already have enough payload in the
form of R/C equipment. And on the larger models, weight builds up
very rapidly. A model doubled in size has four times the area to
paint ... tripling the size multiplies the surface area nine times.
Get the dope onto the model right after the pigments have been agitated
into suspension; allowing them to settle calls for extra coats that
otherwise would not be needed.
For free-flight scale, the
old style colored tissue model with tissue trim or numbers cut from
contrasting colored tissue and doped on appears dead as a dodo.
A full paint job is the order of the day, with flying performance
suffering appreciably. Lucky for us, the engine makers have not
been sleeping; we can still haul the deluxe paint jobs around effectively.
Due to the greater shock hazards inherent in F/F, it is recommended
that you plasticize the dope even more than for Ukie jobs. Two drops
of castor oil per ounce of pigmented dope for tissue-covered models.
So on the flights where the model whacks a pole, tree-trunk or brick
wall there is less chance of splits in the tissue covering. Silk,
being more resistant, will not need heavily plasticized dope ...
no more than 1 drop per ounce.
Weight being an important
factor in F/F scale, you want the maximum pigment coverage with
the minimum number of coats. Since it takes so many coats of white
or other very light shades to "cover," stay away if possible from
designs that call for light paint schemes. Good pigment coverage
is had with red, blue, olive drab and other middling-to-dark shades.
Silver covers very well in just one or two coats. But it accentuates
every wrinkle and scratch in the surface of the model.
to pull masking tape away from a paint job without tearing the covering
or "lifting" the edge of the paint job? When using a brush to apply
pigmented dope along the edge of masking tape, try to avoid painting
the tape. Paint only to the edge if you can. Naturally, you will
"miss" some of the time. Second, don't overdo the number-of-coats
bit. With two dozen coats, you've practically bonded the tape to
the model. On many coats, peel off early, when dope is comparatively
pliable. On few coats, peel late, dope can be quite dry. Pull tape
off with it doubled back running along on itself 180 degrees. This
gives the maximum shearing action where the tape is parting company
with the model. And pull in a slightly side-wise manner, away from
the doped area. The worst you can do is pull at right angles to
the work surface - then you are trying to peel the tissue off too,
to some extent.
To mask off long sweeping curves, a template
is needed, to be sure that the curve is the same on both the left
and right sides of the model. On intricate or small lettering or
trim jobs a steady hand is called for.
Where lettering or
trim exceeds 1/4 to 1/2", a patch of masking tape is laid on glass,
the design then cut into the masking tape with a frisket knife with
point razor-sharp. Granted, it is a major problem just lifting the
masking tape "stencil," aside from properly positioning it on the
model. But the results are worth the effort. It is the only way
a design can be painted on a concave or convex area. A decal will
not lay flat in such an application. On flat surfaces, there is
no problem. Fuel proof decal sheets are available in almost any
color and can be cut to almost any required shape.
with care. A poor construction job can not be hidden under the best
paint job. When the model is built well, when high quality finishing
ingredients are used, the result is a delight to the eye.
Posted December 30, 2012
(Seize the Day!)
Even during the busiest times of my life I have endeavored to maintain some form of model building activity.
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which all began in Mayo, MD. There
is a lot of good information and there are lot
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