This article appears in Sign Builder Illustrated.
Jim Hingst
painter what primers and paints he used when painting MDO. “Why would anyone
today use MDO, when you could paint on Dibond® or Polymetal™?” he responded
brusquely.
that I was expecting and I certainly didn’t need a lesson about the advantages of aluminum composite material (ACM). 30 years earlier, I had
installed Alucobond®, a construction grade composite panel, to clad the fascia of
building. These panels are lightweight, durable and easy to fabricate, using many
of the tools that you would use for carpentry. You can back rout it, bend and
join these panels as well as easily mount them using a variety of extrusions.
of aluminum composite panels are available for sign applications. Comprised of
a thermoplastic core of either polyethylene or polyurethane, these panels are
covered on either side with a coated aluminum skin. The aluminum is typically
between .01” and .012”, which is about half the thickness of the construction
grade material, which is faced with .020 aluminum.
aluminum composite panels. In the sign market, these companies include 3A
Composites, which makes Dibond; Laminators Inc., manufacturer of Omegabond; and
Nudo Products, which produces Polymetal.
panels, we covered the sheets after they were mounted with vinyl graphics. You
can also screen print these composite panels, digitally print them with a flatbed printer and, of course, paint
them.
aluminum composite panel over other substrates, such as MDO is that it is
easier to paint. You also don’t need to fill the edges prior to painting, and, in
many cases, you can paint the panels without a primer, after prepping the surface with isopropyl
alcohol and scuffing it with a Scotch-Brite® pad.
painter, you can hand paint or pinstripe aluminum composite panels with
lettering enamels, such as 1 Shot or Ronan Paints. With the right surface preparation and primer, you can also
use a wide range of other paint systems including latex house paints, lacquers,
urethanes, epoxies, water-borne airbrush paints and acrylic and oil-based paints for fine
art applications.
Surface Preparation
you must first remove the surface protection film and clean the surface. If you
don’t clean the substrate before scuffing or sanding, you can drive the
contaminants into the surface, which can compromise the adhesion of the primer
or paint.
should be sufficient to remove any contaminants. If a sheet has been laying around your shop, you may need to first wipe the surface
with a mild wax and grease remover or xylene. In prepping the surface of ACM panel, do not use any oily solvent, such as mineral spirits or turpentine.
After using a wax and grease remover, a second cleaning with IPA will remove any
residual film that the solvent cleaner will leave. Do not clean the surface
with a glass cleaner containing silicone, such as Windex. Any silicone left on
the substrate can inhibit primer or paint adhesion.
sanding or scuffing, and then clean the panel afterwards.
Isopropyl Alcohol
concentrations, such as 70% and 90%. For surface cleaning prior to painting or
vinyl application, 70% is recommended. The reason is that the higher
concentration evaporates too fast. In removing contaminants for a substrate,
you need dry the surface with a lint-free cloth, while the IPA is wet. After
the alcohol evaporates, it is too late.
As soon as the rag becomes dirty,
discard it and get a new clean rag. You should continue cleaning until you can
wipe the surface and you can no longer observe any dirt on your rag. Until
then, the substrate is still contaminated. You can buy lint-free paint prep rags at an
automotive supply store or on-line from companies, such as Eastwood (www.eastwood.com).
to clean the substrate, you also need to keep your hands clean. Frequently washing your hands prevents your skin oils from contaminating the surface of the panel.
Scuffing the Surface
It is possible to sand a surface to the point that it is too smooth. For this reason, do not use sandpaper finer than 500-grit. Paint needs enough tooth to mechanically lock into the primer.
other than maroon. Each color signifies a different grit range. For sign painting applications, two grades of pads that you should have in your shop are the maroon and the gray pads.
Use
a maroon (red) Scotch-Brite® pad to scuff the gloss or semi-gloss surface of the panel until every shiny area is dull. |
The 7447 general purpose
maroon (red) pads are equivalent to 320-400 grit. Use these Scotch-Brite pads to scuff the substrate. If you prime the substrate, use the gray pads to scuff the primer before painting. This ensures good intercoat adhesion. The 7448 gray Scotch-Brite pads are equivalent to
any residue. Using a lint-free paper towels, continue to clean the panel until
no residue show on the toweling.
NOTE: After sanding or abrading the substrate, never use an air hose to blow off any residue for a couple of reasons. First, the force of the compressed air could blow contaminants into the surface of the panel, which could affect adhesion of the primer or paint. Secondly, blowing the dust off the panel sends it airborne. Not only could you or your employees breathe paint dust, but it takes several hours for the dust to settle. If you paint the panel while the dust is in the air, the dust will likely settle on your paint job.
Clear Coating. You can also use the gray pads to scuff a painted surface prior to clear coating. Unless you are clear coating a metallic paint, these fine scratches will not be visible through the clear coat. The tooth that the scratches give to the painted panel allows the clear coat to grip the surface, preventing sagging on vertical surfaces.
Are Primers Necessary? Some of the panels can be painted directly without the
need of primers. Many sign painters have used aluminum composite panels as
substrates for pinstriping panels. Airbrush artists have also used these panels
for painting. Scuffing the panels using a maroon Scotch-Brite pad is
recommended before airbrushing.
Test, Don’t Guess
pertinent technical bulletins from the panel and paint manufacturers. While this
literature will familiarize you with the proper procedures in decorating the
surface, your responsibility as a manufacturer is to quality the compatibility
of all materials used. That means that you need to conduct your own tests.
These tests range from a simple thumb nail test, in which you use your thumb
nail to scratch the paint or primer from the surface to a cross-hatch test.
to the substrate. You can also use this test to evaluate the intercoat adhesion
between two layers of coatings, such as the adhesion between the primer and
paint.
printed ink sample or paint sample eleven times with an X-Acto® knife and then
scoring the ink again the same number of times over the first set of lines at a
90° angle, forming a grid. The cross hatch pattern of parallel lines should be approximately
1/8” (.32 cm) apart.
burnish an aggressive tape, such as 3M Brand #600 clear tape, over the scored cutlines. The tape is then pulled off 180° against
itself, in one quick motion. If any of the paint comes off, the adhesion of the
ink to the substrate is insufficient. Coatings, which have not formed a strong
bond, are prone to peeling.
Primers
and paints in decorating ACM panels. In the sign industry, many old timers would
use XIM UMA Bonder Primer, when repainting the slick surface of porcelain
signs.
UMA® is a fast-drying, water-based, low VOC primer suitable for either indoor or outdoor applications. It is a great primer for hard-to-stick to surfaces, such as glass, glazed block, tile,
fiberglass and most plastics. Sign makers and artists also use this primer for aluminum composite panel.
Bonder Primer, you can apply a finish
coating using latex paint, waterborne airbrush paint, lettering enamels,
lacquers, epoxies and urethanes.
outdoor applications. You can use it with a variety of paints from lettering
enamels for sign applications to water-borne paints for indoor applications,
such as wall murals. If you are an artist, you can also use this primer instead of a gesso coat.
When priming with a brush, use one with synthetic
bristles. In applying the primer, thin coatings, applied in multiple directions, are much better than applying heavy coats.
One feature of this primer that you should like is that it levels out very nicely. Nevertheless, you should apply a second coat of primer. If the surface is not as smooth as you would like it, you should lightly sand between coats using 320-grit sandpaper or scuff with a gray Scotch-Brite pad.
To aid the primer to level out, you can also add a paint extender to the mixture. To thin UMA add two ounces of XIM Latex X-Tender per gallon.
This primer is usually dry to the touch after an hour and can be
recoated after three hours. Drying times for any primer or paint will vary
depending on ambient temperature and relative humidity.
Allow at least 24 hours for the primer before lightly sanding the surface and painting. When temperatures are
below 70°F and humidity above 50%, allow more time for drying.
Tinting the Primer. Some professional painters advise against adding anything to a primer. As a rule of thumb, primers are generally loaded with the maximum amount of pigment. Attempting to tint a primer changes the ratio of pigment to binder.
If you feel that you need to tint the primer so you can easily see what you have and have not coated, use a universal colorant according the manufacturer’s instructions.
Painting the Graphics. XIM
UMA dries to a really hard finish. Before applying a top coat, you can scuff
the primed surface with a gray Scotch-Brite pad. After scuffing, clean the
surface with IPA. As I began painting the panel, I coated the surface with a
background color. Depending on the paint used and your shop temperature, it
will dry enough to handle in about five hours. After the background paint
cures, you can lay out you job and start painting the graphics, after the paint is fully cured.
you plan to paint a second coat for the background color, you can lightly sand
between the coats. This produces a smoother finish, minimizes an orange peel finish
and promotes good intercoat adhesion. Before applying the second coat, allow
the first coat to dry for at least 24 hours.
Using 320-grit wet/dry sandpaper with a rubber sanding block, you can wet sand the surface by hand. The water helps lubricate the sandpaper so it easily slides over the surface of the paint. The water also prevents the paint from balling up and clogging the sandpaper.
After priming the panel, you can paint the background colors using 1 Shot (http://www.1shot.com) lettering enamels. |
paint mask for this part of the job. The lettering enamel will tack up in about
20 minutes. At this time, you should remove the masking with care, making sure
that no part of the mask touches the wet paint. Do not wait for the paint to
dry or you could tear up some of your newly painted lettering.
In lettering the project, I used 1 Shot lettering enamel. |
Aluminum Composite Panel for Fine Arts.
This panel was primed with two coats of XIM UMA primer. For the painting, I used Golden acrylic paint. |
The advantages of aluminum composite panels for fine arts painting include:
Cutting Aluminum Composite
Panels
composite panels to your size specifications. You can also easily cut it yourself in a number of ways. Cutting on table saw produces a straight
cut. You can also clamp a straight edge to the panel and cut it with a utility
knife.
you should begin with a few light cuts and then continue until you break
through the aluminum skin. This method requires a sharp knife and as many as
fifteen passes. Flip the panel over and cut the opposite side, obviously at the
same location as you first cut.
the panel, the edges can be sharp or have some burrs. To prevent cutting
yourself, deburr the panel by running a flat or mill bastard file over the
edges. Single cut mill files have just a single row of teeth and are sufficient
for smoothing rough edges. Using long strokes with the file, pushing in one direction away from you, this should only
take a couple of light passes. In case the term “bastard” offends you, all it
means is that it is neither medium nor smooth in coarseness, but somewhere in
between.
Conclusion
If you have a paint failure, it is highly unlikely that
the paint itself is the cause. Problems with paint jobs often trace back to the
following factors: substrate preparation; selecting the wrong materials for the
application, incompatibility of raw materials, and finally paint application. To
avoid problems, follow these basic rules, which I have summarized below:
supplies just to save a few dollars never pays.
take the time to follow the procedures recommended in the technical bulletins.
clear coat, always test the materials on the substrate for compatibility.
colors used as well as listing the procedures followed. Include color swatches
in the job folder, as well as any pertinent information, such as contract,
estimate and labor tickets. Good record keeping ensures that if you do the same
or similar job in the future, that you can reproduce your results.
Documentation also can help you, if you need to troubleshoot a problem.