This article appears in the May 2017 issue of Sign Builder Illustrated.
What
makes painting a challenge for sign makers, compared to vinyl application, are
all of the variables. And with each variable the chance that what can go wrong
increases. In fact, it seems that that guy Murphy has stacked the odds against
us. Our only recourse is to identify the causes of our failures and learn how
to avoid mistakes in the future.
Note
that I stipulated “our mistakes”. As much as we would like to blame the
manufacturer for all paint failures, the fact is that in a modern manufacturing
facility with strict process controls, production related problems are
generally less than 1% of material produced. Don’t get me wrong. I don’t
absolve manufacturers of their responsibility. In some rare instances, the
paint itself is out of spec and is the root cause.
The
mistakes that painters are responsible for usually fall into a handful of
categories that I will describe in detail in this article. Often paints fail
because the painter takes a shortcut in surface preparation or is careless in
application. Selecting the wrong product
for a job is another reason paints fail. Extreme environments can also cause
premature failure.
In
troubleshooting paint failures, it is important to thoroughly collect as much
background information as possible. If you keep detailed production records for
each job, many of the answers to your questions should be at your fingertips. Good
photography, careful collection of paint samples and a detailed written
narrative are also critical in documenting problems, when you submit a
complaint to a manufacturer.
While
a sign maker can determine the causes of many coating failures, there is only
so much that he or she can do in the field. A manufacturer has a number of
scientific instruments in their lab that can accurately analyze any samples
that you provide. That’s where the tech people can help. The information that
you provide a manufacturer will help them in making recommendations.
Most
of the problems that you might encounter fall into a handful of categories. Understanding
these primary causes can help you identify the likely reasons for the failure
so you can avoid problems in the future.
Substrate Preparation.
The foundation for a durable paint job is surface
preparation, which includes the following three areas:
1. Cleaning
contaminants from the surface;
2. Proper use of chemicals in pretreating a surface; and
3. Physically roughing up the surface to give it some tooth.
Before
doing anything else, you must prep the substrate to remove contamination. If you
are repainting a painted metal, it is absolutely critical that you remove any
grease, oil or wax before you sand. If
you sand without cleaning, the sanding process will only drive the contaminant
into the substrate causing adhesion failure.
In
wiping a surface down with cleaners, the right way to do it is to do it is to
saturate a clean rag with solvent and wipe the substrate. Before the solvent has time to evaporate, use
a clean dry rag or paper towel to wipe the surface dry. If you just wipe the surface with solvent,
all you end up doing is moving the contaminant from one place on the substrate
to another. Always use the solvents
recommended by the manufacturer.
Failure
to properly prep a surface prior to painting causes a very high percentage of
problems. Contaminated surfaces, for example, can cause blistering. Silicones or
oils on a substrate can result in fish eyes. Contaminants can also lead to
adhesion problems.
Problems When Painting Metal.
Painting
metal is much more difficult than painting wood. What causes most of the paint
failures on metal is surface prep. Here are the usual suspects when troubles
occur:
● The metal was not cleaned properly;
● The paint primer was incompatible with the finish coat; or
● The primer was not been completely dry before the finish
coat was applied.
Painting
aluminum can be especially tricky. Failure to remove the oxidation either
mechanically or chemically prior to painting guarantees adhesion failure. Once you have removed any of the oxidation
from the surface of the metal, you have a limited amount of time before
oxidation occurs again. How much time? Some say about four hours.
To
avoid paint failures on metal or fiberglass some painters recommend using a
self-etching primer. This coating contains an acid that bites into the surface
to promote adhesion.
Paint Selection.
Many times coatings fail because either the primer and
paint were incompatible with the substrate or the wrong paint was selected for
the service environment. Sign makers work with many different types of
substrates. Each substrate has its own set of requirements, including surface
preparation, primer and paint system.
Matched Components.
For the best results and to avoid problems
such as the paint crazing or cracking, use a primer, paint, reducer and clear
coat from the same manufacturer. This ensures that the different materials are
all matched for compatibility.
Be
careful when adding any solvent to the paint to thin it out. Paints are carefully formulated so that all
of the ingredients are compatible with each other. Mixing an incompatible solvent with a paint
can lead to disastrous results, such as cracking and wrinkling. If you need to thin a paint, it is best to
use the manufacturer’s product. Some solvents flash off too fast, resulting
in the outer layer of paint dying before the layer below it is fully cured. By
trapping unevaporated solvents beneath the skin of the paint, the coating never
fully hardens.
You
also need to follow the paint manufacturer’s recommendations regarding
compatibility of primer, paint and clear coat. The chemistry of these
components is very complex and each part of the system interacts with the other. By
following the manufacturers guidelines, you will achieve better looking, more
durable results and encounter fewer problems.
Plastics.
While
matching the components of a paint system is critical in avoiding problems, it
is also important that the paint is compatible with the substrate, especially
when painting a plastic substrate. The surface energy of a material directly
affects paint adhesion. Solvents used in surface prep and thinning of the paint
can affect the performance of the plastic sheet.
Because
various plastics are formulated and processed differently, each can have its
own unique characteristics, requiring special consideration and treatment prior
to painting. For this reason, before
spray painting either acrylic or polycarbonate sheet, carefully read the
manufacturer’s technical bulletin and follow their recommendations regarding
surface preparation, primers, approved solvents and paints, and spraying
techniques. In thinning the painting, use the recommended solvents and never
substitute with unapproved solvents.
Strong
solvents in the paint subject the plastic sheet to a chemical stress. That chemical stress, in addition to the
mechanical stresses that are subjected upon the sheet during fabrication, can
greatly reduce its impact resistance, which can contribute to breakage.
Primer Selection.
Selection
of a paint primer, which is the foundation for a good paint job, is also critical. Contrary
to what many say, it is not just a cheap paint. It serves a couple of basic and
very important functions:
First,
when painting a porous substrate, such as drywall or wood, it seals the
surface. In some cases, it can serve as a barrier coating. For example, a latex
primer, such as Zinsser BullsEye 1-2-3 Primer is more effective than oil based
primers at blocking tannins in a wood substrate from bleeding through the
paint. Applied to an non-porous
substrate, such as high-density urethane (HDU), the thick coating can fill in
the sandpaper-like surface, transforming it to a smooth, even finish.
Primers
are also critical in anchoring or bonding the finish coat to the substrate.
That’s why selecting the right primer has a direct impact on the durability of
the paint job.
Paint Application.
Thick coatings of paint often result in problems such as
wrinkling or sagging. Heavy applications of paint can also cause mud cracking
in which the paint has the cracked appearance of dried mud. Other reasons for
cracking are not allowing enough time for a coat of paint to flash off before
painting a subsequent coating of paint or failure to sufficiently stir the
paint before use.
A
heavy application of paint, though, isn’t the only reason that paint can sag or
run. Adding too much thinner also makes a paint too runny. That’s why its important to reduce your paint
according to the manufacturer’s instructions.
High ambient temperatures can also thin the viscosity of the paint,
making it watery.
Drying and Curing.
The conditions under which a coating cures or dries can affect
the paint’s appearance and performance. In addition to its binder or resin and
its pigment, paints contain water or solvent, which evaporate during drying or
curing. When water or solvent becomes trapped within the paint or the paint
dries too quickly, problems occur. Here are some of those problems:
High
temperatures can cause solvents in a paint system to evaporate too quickly
causing pinholes.
If
any moisture is trapped in a wood substrate and does not breathe out of the
wood, the trapped moisture can cause blisters or peeling paint. Other causes of blistering include painting in
a humid environment and not allowing the substrate to dry sufficiently after
wet sanding.
To
prevent moisture related problems only paint when substrates that are
thoroughly dry. Avoid spraying when the
weather is humid. It’s usually better to wait until conditions are right. If
you are pressed for time, and are force to paint when humidity is high, add a
retarder to your paint and allow for some extra flash time.
To
prevent trapped solvents you can take a number of precautions. These
precautions include:
(1)
Only use reducers that the paint manufacturer recommends.
(2)
Always follow the manufacturer’s application guidelines.
(3) Between coats of paint, follow the manufacturer’s
guidelines regarding drying time. Also be aware that some finish paints dry so hard
that if you wait too long before painting another coat, you can have problems
with inter-coat adhesion. In some cases, if too much time is allowed,
components in the paint can bloom to the surface, which can prevent the
subsequent coat of paint from adhering to the primer coat. Top coats of paint should be applied within a
couple of weeks after the primer is applied.
(4) Avoid painting heavy coats of paints. Instead paint
lighter coatings and allow sufficient time between coats for the solvents to
evaporate.
Environmental Damage.
Prior to manufacturing, survey the application and make
sure that you thoroughly understand the conditions to which the sign will be
subjected. This will help you select the right paint primer and finish paint for the job. Some of
the environmental extremes that cause paint problems are UV light, heat, cold
and moisture.
In
some regards we are at the mercy of the weather. Is there anything that we can
do other than complain? The answer is yes! The purpose of a site survey is to
identify the potential problems and select the materials that prevent premature
deterioration.
Temperature
extremes, especially high temperatures, can prematurely age both painted and
applied graphics. Intercoat peeling can also occur, if the undercoat of paint
was not properly prepared. Sanding
between coats can give the undercoating some tooth, which will promote and
ensure good adhesion between layers of paint.
Moisture
causes countless problems with wood signs. Many of these problems start at the
edges of the sign, where moisture can enter. See the photo below. To avoid deterioration at the
edges you should fill any gaps in the wood and use a round over bit to smooth
the sharp edges, which are prone to chipping and splintering.
Conclusion
Properly
applied, a painted sign can provide up to 10 years of service life or more. To ensure
the maximum durability from your paint job and to avoid problems here is a summary
of my suggestions:
1. Read the Manufacturer’s Technical Information.
I started this article,
stating that what made painting so difficult were all of the variables that
increased the odds of making mistakes. Put the odds in your favor by doing your
homework. Read the manufacturer’s literature and follow their guidelines.
2. Ask for Help.
No one has all of the answers. You just need to know
where to find them. I have been lucky enough to make friends with some of the
most experienced sign painters in the business, who can provide me with
reliable advice, when I have a question.
3. Ask Better Questions.
To paraphrase self-help guru, Anthony Robbins, if you want better
answers, ask better questions. This is especially true when you are
troubleshooting a problem. In asking questions, remember the Rudyard Kipling’s six
honest serving men who taught him everything he knew: who, what, why, when,
where and how.
4. Test, Don’t Guess.
Albert Einstein said that “a person who never made a
mistake never tried anything new.” You should keep your mind open to new products,
new ideas and new ways of doing things. However, I would much rather avoid
mistakes altogether. That’s why I suggest that if you are trying out something
new a new, test it first.
Before
production, test the paint on the substrate for good adhesion by performing a
simple tape test or a cross hatch test. When spray painting it is also a good idea to spray some test panels habit, just to check whether the paint
is thinned to the right viscosity or to check your air pressure settings are
correct.
5. Document Your Paint Processes.
Sometimes when you are making something new for the
first time, you have to learn how to do it right. As you are going through your
learning process, document what you did, so you can reproduce your results.
6. Stick with What Works.
As you can tell, I believe in trying new products, and
new paint processes. But as one of my friends in the industry told me, “if it works,
continue to do it. If it doesn’t, then try something else.”
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About Jim Hingst: After fourteen years as Business Development Manager at RTape, Jim Hingst retired. He was involved in many facets of the company’s business, including marketing, sales, product development and technical service.
Hingst began his career 42 years ago in the graphic arts field creating and producing advertising and promotional materials for a large test equipment manufacturer. Working for offset printers, large format screen printers, vinyl film manufacturers, and application tape companies, his experience included estimating, production planning, purchasing and production art, as well as sales and marketing. In his capacity as a salesman, Hingst was recognized with numerous sales achievement awards.
Drawing on his experience in production and as graphics installation subcontractor, Hingst provided the industry with practical advice, publishing more than 150 articles for publications, such as Signs Canada, SignCraft, Signs of the Times, Screen Printing, Sign and Digital Graphics and Sign Builder Illustrated. He also posted more than 450 stories on his blog (hingstssignpost.blogspot.com). In 2007 Hingst’s book, Vinyl Sign Techniques, was published. Vinyl Sign Techniques is available at sign supply distributors and at Amazon.
© 2017 Jim Hingst
Thanks for sharing this info!
ReplyDeleteThat was quite illuminating
Elcometer