Getting that Great Looking Finish
A beautiful, professional quality finish adds that
all-important final touch to your model. It's what gets
those extra stares at the field…and makes you proud ofa
job well done. Some expert builders would have you
believe that covering is an art that takes years of
experience to develop, but the truth is that you can
achieve it with some basic know-how and patience.
Understanding the materials you're working with is
vitally important, and, surprisingly, this is where many
modelers make the biggest mistakes. Each brand of
covering has unique properties. So if you learn using
one type of covering and then try using those techniques
with a different brand, it often leads to marginal
results. I've been using UltraCote exclusively for the
last 15 years. UltraCote offers several unique
properties that are advantageous over other film
coverings, making it easier for me to achieve and
maintain a professional finish. Applying UltraCote
requires its own learned techniques.
Multi-temperature, Maximum Control
UltraCote is unique in that different things happen at
different temperatures. This allows for precise control
Covering with UltraCote becomes many times easier– with
vastly improved results – when you understand what
specific temperatures do to UltraCote, and when to use
The adhesive is activated at just over 200º F. At the
recommended application temperature of 220º, the
adhesive reaches its full bonding strength. No shrinkage
of the film occurs, so no distortion of the film takes
place. Use the 220º application temperature when
applying covering and when applying UltraCote trim
pieces over UltraCote. Remember, if your iron is set at
220º, no shrinkage or distortion will occur, so there is
no risk of distorting seams, trim lines or trim pieces
and full bonding strength occurs.
Watch out for…
Don't press! Heat liquefies the adhesive, not pressure.
Let the heat do the work and avoid gouges. It's natural
to want to apply pressure, but it doesn't affect the
bonding strength. If you're using a sock (highly
recommended), it will be necessary to go more slowly
over a given area, as it takes longer for the heat to
penetrate the material. Some modelers turn up the heat
to 240º when using a sock, but I prefer to stick with
the 220º temperature and go at a slightly slower pace.
This creates fewer air bubbles.
300°F- Shrink Onset
At 300ºF, UltraCote will begin to shrink. Use this
temperature after the covering is applied to tighten it,
remove wrinkles and remove imperfections. It's amazing
how many wrinkles can be removed at this temperature,
and it's important to start removing imperfections at
this minimum shrink 300º setting. UltraCote features a
unique property that allows for a controlled shrink rate
based on the selected temperature. While it begins to
shrink at 300º, at 320º, UltraCote shrinks 18% of its
total shrink rate (see chart). It's important to use the
minimum temperature necessary to achieve a smooth
wrinkle-free finish. Most modelers don't realize that to
further shrink most brands of film covering, it must be
heated above its previously exposed peak temperature. In
other words, if a covering was already exposed to 320º,
it will be necessary to go above 320º to further shrink
the covering. Use the lowest temperature possible to
achieve a smooth wrinkle-free finish at the start and
you'll have the largest available shrink rate remaining,
should you later need to shrink the film.
Watch out for…
Stay away from seam lines and edges! Remember, 300º is
well above the adhesive activation temperature, and
seams will pull away. If you have some stubborn wrinkles
close to the seam line, try this trick. Soak a washcloth
in cold water, then fold it twice and place it on the
seam line, covering the seam but exposing the wrinkles.
With your iron at 330º, quickly apply it to the wrinkled
area (about 5-10 seconds). The washcloth will keep the
seam cool, and prevent it from pulling apart and
350°F- Maximum Shrink
At 350ºF, the maximum shrink is achieved. You won't use
this setting very often, but it's important to know the
total shrink temperature range. That's because the
amount of shrink rate you'll have left is based on the
temperature you use to shrink the covering.
For example, if you're shrinking your film using 320º,
by referring to the chart, you'll find that 82% of the
total remaining shrink is left. That's good! That means
that, if in the future you need to re-shrink the
covering, it won't be a problem. But a word of caution:
use the highest temperatures only as a last resort to
shrink wrinkles and imperfections. In most cases, if you
need to use this much heat, you'd be better off to just
replace the covering with a new piece.
Watch out for…
Stay away from seams and edges. This high temperature
can cause bubbling and blistering.
You may come to a point when you'll need to remove or
replace a piece of UltraCote.
In many cases, the covering will simply pull away, but
if you're having a tough time, use your heat gun. Lift a
corner of the covering, and then pull away while
directing heat in the area to be removed. I just
recovered the 2-year-old Reebok CAP 232 using this heat
gun technique, and it looks as good as new!
Bubbles and Blemishes
When your airplane sits out on a hot sunny day, you may
notice that the covering bubbles and wrinkles. This is
common with all brands of film covering, no matter what
the manufacturers claim. But getting rid of those
wrinkles is easy. You'll need a heat gun, a covering
mitt, a wet washcloth, and a fine straight pin.
Heat the affected area, and notice how the air
underneath the covering expands, making bubbles. As you
continue to apply heat, moving in a 6” circle, it will
release the adhesive bond. At first, several small
bubbles will appear, but as you continue to work the
area, the bubbles will join to form one large bubble.
Now pop the bubble with the pin, and immediately wipe
the area with a covering mitt to reattach the covering.
It may take several attempts, and you'll get better
after you do it a couple of times.
It's important to not stay in one place for very long
with the heat gun, especially if you're working with a
balsa-covered foam part, as warping and damage could
occur. If the affected area is close to a seam, use the
wet washcloth trick to prevent the seams from distorting
and pulling apart.
Preventing Heat Blemishes
Heat blemishes occur when the elevated temperature
causes the trapped air in the wood to expand. With
nowhere to go, the expanded air causes a bubble to form
in the covering and stretches the film. When the air
cools, the stretched covering remains. You'll notice
this happens especially with dark colors like black or
dark blue, and that this never happens on the bottom of
the wing, but only the top where the sun heats the
The solution? While several methods have been tried—like
completely painting the wood structure with thinned
white glue to prevent the air from reaching the
surface—we know of only one method of preventing this
from happening: don't leave your airplane in the sun!
Seriously, get a cover or a tent or find some shade.
Also, choosing light colors will prevent the intense
heat buildup. Last summer during our hottest days, I
measured the covering temperature on a dark blue
airplane that had been sitting in the sun at 163º. If
you keep them from getting hot, there is no problem,
but, for those times when they do, practice the
re-shrinking techniques mentioned above, and it will
only take a few minutes to bring back that pristine
by John Adams