Preventing and Troubleshooting Paint Problems
By Jim Hingst
Murphy’s Law must have been written with
paint in mind. Like many other people, I learned what to do and what not to do
when painting, after experiencing paint problems or less than satisfactory results. These
painful experiences have taught me valuable lessons which I would like to pass
on to you.
Running
or Sagging Paint.
Whether you are applied
paint with a brush or a sprayer sometimes you just lay it on too thick. This can result in drip or long strokes of
paint that start to droop. This is one reason that it is always better to paint
thin coats of paint. Scuffing up the
surface a little with 220 grit sandpaper or a grey Scotchbrite® pad will also
give the substrate a little tooth, helping prevent the paint from running.
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 it is important to reduce your paint according to the
manufacturer’s instructions. If you are
shooting a urethane you should precisely measure paint, hardener and thinner.
High temperatures can also thin the viscosity of the paint, making it watery.
Blisters.
A number of conditions can cause blistering. A common cause of blisters is moisture
trapped underneath a painted substrate. This often happens, if a porous
surface, such as wood sign blank, is not thoroughly dry before it is painted. As
the moisture comes out of the wet substrate, blisters can form.
Other causes of blistering include painting in a humid
environment, moisture in the air lines when spray painting 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 moisture in the air lines
from contaminating your paint, get into the habit of draining moisture from
your compressor and air lines regularly.
Moisture isn’t the only cause of blistering. Blisters can
also result if the substrate is rusted or contaminated, or if solvent is
trapped beneath the paint. Proper substrate preparation using recommended
procedures and the appropriate solvents and chemicals is essential to rid the surface
of troublesome grease, oil and rust.
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, allow sufficient time for the
solvent to flash off.
(4) Allow enough
time for the primer to cure before painting and for the paint to cure before
clear coating.
(5) Avoid painting heavy coats of paints. Instead paint
lighter coatings and allow sufficient time between coats for the solvents to
evaporate.
Taking these precautions will help you avoid problems as
well as the time and expense required to correct them. Generally, the remedy for paint blisters
involves stripping off the paint from the area affected and repainting the
substrate.
Craters.
An important part of producing a quality
paint job depends on how well your spray gun atomizes the paint. Whereas silicone and dirt can cause fisheyes, which are
craters that form around the contaminant, tiny bubbles that are trapped in the
coating can rise to the surface and pop, while the paint is still wet, causing
craters.
Often, air is trapped in the paint, if the spray gun doesn’t sufficiently
atomize the paint. A simple remedy is to increase the air pressure. Air can
also be trapped in the paint for other reasons. These include holding spray gun
too close to the substrate and spraying at a slow rate of movement.
Cracking.
The appearance of cracked paint resembles the cracked
surface of dried mud. Common causes of cracked paint include applying too heavy
of a coating of paint; not allowing enough time for a coat of paint to flash
off before painting a subsequent coating of paint; failure to sufficiently stir
the paint before use; and failure to mix the correct ratios of paint to
hardener. One practice to reduce the occurance of cracking paint is to always
take time to thoroughly stir the paint before use.
When spray painting, spray light coats of paint,
allowing enough time between coats for the solvent in the paint to flash off.
If you run into a problem and the paint cracks, there is no quick fix. The
failed paint must be removed before repainting.
Matched Components. For the best results and to avoid
problems such as the paint crazing or cracking, the best advice is to use
primer, paint, reducer and clear coat from the same manufacturer. This ensures
that all of the components are matched for compatibility.
Mixing ingredients from
different manufacturers is often a recipe for disaster. Trying to save a few nickels on a cheaper
competitive product that is not recommended by the paint manufacturer, will
often cost you dollars later in rework and loss of customer goodwill, if the
components turn out to be incompatible.
“Test,
don’t guess.” Painting involves variables. Lots
of them. These variables include the substrate, the primer, paint, clear coat,
your procedures and your shop environment, which can vary in temperature and
humidity as the seasons change. Before
you use new materials and new techniques, play it safe and test the coatings on
a scrap piece of the substrate to ensure your success on a real job.
Whenever you paint a
substrate, keep a record of what type of primer, paint and clear coat used and
the color formulation. Maintaining this information will ensure that you can
match colors and reproduce your results on repeat orders.
Fisheyes.
Spraying a substrate, which has been contaminated
with silicone, oil or grease, is the usual suspect, when fisheyes occur. To
prevent contaminants from causing problems, surfaces should be cleaned
thoroughly before painting according to the recommendations of the substrate
and paint manufacturers.
When prepping surfaces, never use a substitute
for the cleaners recommended and always wipe the surface dry with clean rags or
plain white paper toweling. Oil in the air lines can also result in fisheyes.
To ensure that the air that reaches your spray gun is clean and dry, you will
need to install filters in the supply line to remove moisture, oil and
dirt. As part of your maintenance
program, you should drain and clean the air lines regularly and periodically
change the filters.
Adding a fisheye eliminator, such as
Marson’s Smoothie, to your paint can help prevent fisheyes. An 8oz. bottle of
Smoothie costs between $15 and $20. It
is ironic, though, spraying a previously painted substrate that has some fisheye
eliminator residue on it can also cause fisheyes. When painting a vehicle
substrate, paint companies generally recommend against adding fisheye
eliminator to base coats. If fisheyes appear in a painted surface, there’s not
much that you can do other than sand the affected surface until the little
craters disappear.
Orange Peel.
The term “orange peel” is used to describe a painted surface with a texture
that looks like the skin of an orange. Orange peel can result from a number of
causes. One reason this problem can occur is that the viscosity of the paint is
too thick, which inhibits the coating from adequately flowing out onto the
substrate.
Thinning the paint to the consistency of milk, faithfully following the
manufacturer’s instructions and only using recommended thinners can help prevent
orange peel. Shop environment will often determine which thinner or reducer you
will want to use. Using a thinner that evaporates too fast can also contribute
to orange peel. In selecting a thinner which will be suitable for the
conditions in your shop (temperature, humidity, etc.), follow the advice in the
product bulletin of the paint manufacturer.
Other reasons for orange peel
include low air pressure. Air pressure settings will vary depending on the viscosity
of the paint. You will need to spray a test pattern and adjust your gun
accordingly, prior to painting, to adequately atomize the coating. Always use
the fluid tip, needle and air cap recommended for the particular coating that
you are spraying.
Poor painting technique can also cause orange peel. Spraying on an
overly thick coating of paint can result in an orange peel texture. When you
are painting, concentrate on what you are doing and adjust your spraying
technique based on the results that you are producing. This may mean altering
the speed at which you are spraying or the amount of paint overlap.
Wrinkling.
When spraying a surface, it is better to apply thin coats of
painting than laying it on thick. Spraying excessively thick layers of paint
can cause the paint to shrivel up like the skin of an alligator. Other causes of wrinkling include: (1) using
a very hot solvent to thin a paint; (2) using a clear coat that is incompatible
with the paint; (3) painting in a hot, humid environment or exposing a newly
painted surface to high heat. To remedy a paint finish that has wrinkled, usually
requires sanding the affected area.
Each paint system is little different
from the rest. For that reason, you need
to pay strict attention to the manufacturer’s instructions. Always read the
technical bulletins that pertain to the coating, before you use it. It doesn’t do you much good to screw up a
job, and the try to figure out where you went wrong. You certainly will
remember and learn from your painful mistakes. But I just think that it’s
better to avoid problems, when you can.
Paints, which are clear coated, can
wrinkle for a variety of reasons. Some paints can wrinkle, if the paint cures
too long before clear coating. The recommended procedure for spraying their
urethane paints is to apply a color coat, let the solvents flash off, then
shoot the next color coat. The first
coat should still be tacky, not hard, when you apply the subsequent coat. You
should not sand the painted surface between coat.
After spraying the urethane color, you
should spray the clear coat before the color coat completely hardens. This
ensures that as the color coat finishes its curing process, it chemically bonds
with the clear coat.
After the first coating of clear coat
cures for 24 hours, the surface should be wet sanded with 600 grit sandpaper or
finer, and then sprayed with a second coat.
Spraying a second coat of clear coat on a first coating which has not
fully cured can result in problems, such as delamination.
Delamination of the clear coat from the
base coat can occur if you don’t wait long enough for the solvents to flash
off. I realize that this sounds like a contradiction of what I said earlier.
You can’t wait too long before you clear coat, but you must wait long enough.
It sounds like double talk, but it’s not.
It’s like hitting a baseball. If you swing too soon or swing too late,
you’ll wiff. The timing has to be just right.
Chalking.
Chalking is the white powder that appears on the surface of old,
oxidized paint. On vehicle surfaces, you can minimize chalking from
accumulating by regularly washing the vehicle.
These washings will remove the powdery residue as it starts to
accumulate. Using a polishing compound
can also remove some of the chalking.
But if it gets out of control, the only remedy is to use a Scotchbrite
pad or sandpaper to remove the weathered paint.
While chalking results as any paint weathers, poor spraying application
of the paint can contribute to this condition.
As paint
weathers in sunlight (UV light attacks and degrades the resin that binds the
paint ingredients), it oxidizes and gradually erodes, leaving a powdery residue
of pigment on the surface of the substrate. Chalking is actually a quite common
and natural occurance with lighter colors, especially if you have used a lower
quality oil-based paint.
Chalking should not cause alarm — it is
the result of the normal aging process. All oil-based paints chalk. Chalking
doesn’t occur overnight. Generally, it
takes years before the resin degrades and chalk appears. High temperatures and overexposure to ultra-violet
light, however, will accelerate the aging and fading process.
Over thinning a paint can also cause
premature and excessive chalking. The lesson to learn is to only use reducers,
which are compatible with the paint system, and always thin paint according to
the manufacturer’s instructions. Very light coats of paint and lower quality
paints are also more prone to excessive chalking. The best practice is to
invest in the best paint that you can afford. Remember that there are no
shortcuts to quality and value. If you buy a cheap paint and it fails, you
haven’t saved any money.
Whether
you are painting graphics or applying vinyl graphics, any chalking must be
removed before you start decorating the surface. I can guarantee you, that if
you fail to clean chalking from the substrate, the graphics will fail. The
reason is that the chalk will form a barrier preventing either the painted
graphics or the pressure-sensitive adhesive on the vinyl from adhering.
The degree
of chalking and the substrate’s condition will differ from one substrate to
another and for this reason strict rules for substrate preparation don’t exist.
That’s why chalking removal may require experimentation.
Some
experts suggest using a power washer to flush the surface with clean, warm
water, while others contend that even high-pressure power washing only removes
a minimal amount of residue.
If you opt
to use a power washer, exercise extreme caution. Excessive water pressure can
literally blow the existing paint off a substrate. Be sure to keep the tip of
the washing wand at least one foot from the surface.
Don’t try
to wash chalk away with a solvent cleaner, especially a petroleum-based product
such as Prep Sol™. A chalky surface is a layer of dead paint, which will absorb
the solvent like a sponge. Rather than cleaning the surface, the solvent will
turn the white powder into a white paste, which will merely smear around the
paint surface. Some chalk and dirt will be driven back into the paint, and the
chalk will eventually float back to the surface causing problems at a later
date.
Abrading
the surface is often the best — although certainly not the easiest — solution
for cleaning a chalky substrate. Many painters and decal installers use
Scotchbrite® pads, which is similar to a kitchen scouring pad, and water to
clean the surface. Cleaning with these pads will require plenty of elbow grease
and clean rags to mop up the considerable mess.
Scouring
pads effectively abrade chalk from the substrate, but they will also scratch
the surface. When refurbishing a sign,
you will usually need to repaint the background. If you are decorating a vehicle surface, such
as a trailer, this may not be practical.
In most cases, the scratches on the substrate should be acceptable. On a truck surface, they certainly won’t look
any worse than the chalking did.
In the
past, some sign makers have used polishing or rubbing compounds to remove
chalking. Be sure to select one without wax, because such cleaners leave a
residue that can compromise the adhesion of anything painted or applied to the
surface.
For a
lightly chalked surface, I suggest using powdered cleaners with mild abrasives.
In addition to removing the dead paint, these cleaners will scuff the paint,
providing more surface area for the painted graphics to adhere to.
About Jim Hingst: Sign business authority on vehicle wraps, vinyl graphics, screen printing, marketing, sales, gold leaf, woodcarving and painting.
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 190 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 500 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.
© 2019 Jim Hingst, All Rights Reserved.
Tidak ada komentar :
Posting Komentar
Leave A Comment...