ou might think that conducting

paint-weathering tests is about as

exciting as watching paint dry, only

a lot slower.

Admittedly, not too much has

changed in weather-testing coat-

ings by placing test specimens on “test

fences” at original equipment manufacturer

(OEM) or commercial “test farms.” In fact,

even those colloquial terms, test fences and

test farms, are throwbacks to the first doc-

umented paint exposure tests, begun in 1906

at the Government Agricultural Experiment

Station in Fargo, N.D.

About the only significant changes in “sta-

tic weathering” since then are that the expo-

sure racks now face toward or away from

the equator for mildew tests, rather than

east-west; and that the severe climate of

South Florida has become the standard

benchmark reference instead of Fargo.

Of course, the variety of architectural,

protective and functional coatings, as well as

the range of substrate materials, has

evolved and expanded tremendously since

those days. And while the majority of test

specimens are still coatings on metal panels

or lumber “trade panels,” a walk through a

test-farm reveals no end of specimen types,

from beams and pipes running through con-

crete and masonry walls, to products such

as outdoor furniture.

42 D+D OCTOBER 2014

Y

Coatings A to Zielnik

How Paint WeathersPaints and coatings weather in many ways,

depending on their formulation chemistry, the

substrate and the climate. Even the definition

of “failure” varies, often subjectively. For

some coatings, such as architectural and au-

tomotive, appearance properties such as color

and gloss retention are paramount. For oth-

ers, protecting the substrate is the main

criterion.

In some cases, both are required. The

Florida Department of Transportation, for ex-

ample, has much higher standards for bridge-

coating appearance than do most other

states, owing to Florida’s dependence on

tourism. After all, they have to keep up with

Disney.

So what causes paint to weather? For most

coatings, solar radiation, and particularly its

ultraviolet (UV) component, degrades the paint

film along with temperature and moisture.

These stresses are interconnected and also

vary with the natural daily and seasonal cy-

cles. Film-forming resins can photo-degrade,

resulting in surface erosion which leads to

chalking and loss of gloss, or loss of adhesion

to the substrate.

In the case of wood coatings, sunlight can

degrade the wood’s lignin and cellulose, caus-

ing adhesion loss. UV and visible sunlight can

also fade pigments, resulting in color loss.

Architects often ask me if I know a high-

chroma red that won’t fade to pink.

Yellowing of the binder or loss of a pigment

can cause hue-shift.

High temperatures can accelerate some of

the degradation chemistry, with darker colors

usually growing hotter than lighter colors.

Temperature cycles affect coating moisture

levels and cause thermo-mechanical stress on

the coating and adhesion boundary, especially

as the substrate expands and contracts.

Temperature cycles also help drive coating

moisture cycles. These, in combination with

sunlight, can cause coatings to micro-crack,

blister and lose adhesion.

It’s that aspect — high levels of solar radia-

tion and warm temperatures combined with

plenty of moisture — that makes the subtropical

southern tip of Florida so harsh on coatings —

and other organics and polymers such as plas-

tics. Arizona’s Sonoran Desert, another weath-

ering benchmark climate, is much hotter in

summer and colder in winter than Miami, and

has about 19 percent higher annual UV totals.

But with an average of only about 9 percent of

Miami’s coating “wet time” (measureable

surface moisture), we see only a fraction of

South Florida’s weathering in the dry desert.

By Allen Zielnik, Atlas Material Testing

Technology LLC

Outdoor Testing Never Lies Laboratory weather testing

of coatings has come a long way, but exposure to the elements is still king.

Coatings A to Zielnik43

This points out how important moisture is,

in balance with the other stresses of heat

and solar radiation. So is the South Florida

climate unique in the world? Clearly not; in

fact, some locations have harsher condi-

tions. But due to its long history, historical

data and easy logistics, South Florida has

become the de facto global benchmark loca-

tion for coating testing. In addition to Atlas’

South Florida Test Service, established in

1931, the location hosts several coating

OEM sites, including those of PPG, DuPont

and Valspar.

Hurrying It Up The balance of the main weathering factors

and their natural cycles presents a dilemma in

weathering testing. As Warren Ketola, a well-

known researcher at 3M’s Weathering Re-

source Center, was fond of saying, “Outdoor

testing never lies.” The problem is that it

takes a long time to generate data, especially

in coating formulation development. Re-

searchers have tried various ways of acceler-

ating natural weathering.

For instance, the EMMA (Equatorial Mount

with Mirrors for Acceleration) Fresnel solar

concentrator was originally developed in 1958

by DSET Laboratories in New River, Ariz. It is

a solar tracker with 10 special mirrors to con-

centrate direct-beam solar radiation onto the

test specimens. It requires the dry desert air

to operate — high humidity or clouds scatter

UV in the atmosphere.

Equatorial Mount with Mirrors for Accelera-

tion with Water, or EMMAQUA, simulates the

rain and nighttime condensation of South

Florida, with custom-programmed sprays of

deionized water during the day, and at night

when the device inverts so the test specimens

Countless coatings samples face a harsh environment for prolonged times at a South Florida test site in this photo taken with a fish eye lens.Photos courtesy of Atlas Materials Testing Inc.

Weather-Ometer was an enhancement of

the textile lightfastness color Fade-Ometer

instruments used since 1919. The original

devices used one of two types of electrically

burning carbon arc lamp technologies. These

represented the best simulation of sunlight at

the time.

However, they had serious spectral mis-

matches in the UV and visible wavelengths

which could distort the underlying photochem-

ical processes and, thus, the weathering test

results. Nonetheless, the technique of artifi-

cial weathering for coatings was established,

especially for comparative purposes, though

less useful as a lifetime predictor.

The quest for a better sunlight simulator

made a major leap forward when the xenon

arc gas discharge lamp debuted in Atlas’

Xenotest instrument in 1955. With proper

optical filtering, the xenon arc lamp provides

the closest full-spectrum sunlight simulation.

The spectral match in the UV and visible por-

tions is critical for reproducing the photo-

chemical processes that occur outdoors for

the coating binder, colorants and performance

additives. The near infrared (IR) match is also

important so that specimen temperature,

which varies with IR absorptivity (e.g., coating

color), and its effect on coating moisture con-

point skyward. Special temperature controls

can provide a variety of test conditions. The

technique is subject to the varying sunlight

and weather of the seasons, but does apply

about four times Miami’s annual total ultravio-

let solar radiation on a typical 45-degree in-

clined south-facing exposure rack in one year.

A UA (ultra-accelerated)-EMMAQUA

debuted in 2014. This advanced version uses

20 specialized “cool” mirrors that reflect

solar radiation in the UV and near-visible

(<500 nm) region to increase the UV intensi-

fication factor 10 to 12 times while simulta-

neously eliminating excess heat from the

near-infrared portion of sunlight.

The U.S. Department of Energy National

Renewable Energy Laboratory and Atlas

co-developed this specialized mirror technol-

ogy. It was first used in the Ultra Accelerated

Weathering System (UAWS), which intensifies

annual Miami UV 63 times.

44 D+D OCTOBER 2014

Bringing the Outdoors InOne problematic aspect

of both natural and

accelerated outdoor

testing is that “climate

is what you expect;

weather is what you

get.” This makes com-

paring outdoor test

results from different

time periods difficult,

especially if tests

began in different

seasons.

For a more consis-

tent and reproducible

test environment,

researchers have artificially weathered sam-

ples in the laboratory since 1927. That’s when

the Weather-Ometer was introduced. The

This photo shows the inside of an artificial laboratory weather instrument or “Weather-Ometer.”The machine reproduces and accelerates the effects of full-spectrum solar radiation, temperature,humidity and rain/condensation on the racks of colored samples, but at an accelerated pace.

At a South Florida test facility, samples are angled toward the sun for maxi-mum solar radiation exposure, and are attached to a backing, increasingspecimen temperature, similar to conditions on a building.

ASTM D7869

It is being called “the most thoroughly researched weathering test procedure ever developed.”

Attend a free webinar and get your free copy, compliments of Q-Lab:

for automotive, railway, aerospace, and

other transportation coatings

www.q-lab.com/newASTM

It is being called “the

It is being called “the weathering test procedure ever developed.”

It is being called “the oughly researched most thorweathering test procedure ever developed.”

oughly researched weathering test procedure ever developed.”

oughly researched

ASTM D7869for automotive, railway

other transpor

ASTM D7869, aeros otive, railway y, aerospace, and

tation coatings

ASTM D7869, aerospace, and

tation coatings

Attend a

Attend a free webinar and get your

other transpor

webinar and get your free copy

tation coatingsother transpor

, compliments of Q opy y, compliments of Q-Lab:

tation coatings

, compliments of Q-Lab:

.q-lab.comwwww.q-lab.com/newASTM

.q-lab.com/newASTM

Click our Reader e-Card at durabilityanddesign.com/ric

46 D+D OCTOBER 2014

tent and secondary chemical reactions are

also correct.

Xenon arc artificial weathering combines

the stresses of full spectrum solar radiation,

relative humidity, water sprays and elevated

temperatures under either steady-state or

cyclic conditions, depending on the test proto-

col used. It offers the ability to alter the indi-

vidual parameters to probe the coating for

individual or combined stress sensitivities.

With the proper choice of conditions, it can,

within limits, simulate various climates.

Researchers use Xenon arc artificial weather-

ing for relative comparisons under prescribed

conditions, or to determine failure modes and

estimate the service lifetime of coatings,

although the latter is complex and only in

its infancy.

UV emission at 313 nm. The other is the UVA-

340 which peaks at 340 nm. Both lack the

higher visible and near infrared wavelengths

of sunlight.

The UVB lamp has wavelengths well below

that of natural sunlight and was once popular,

since some researchers believed that the

extra UV would increase test acceleration.

However, given the possibility of radically

altering the natural photo-degradation path-

ways, and producing different but not neces-

sarily faster results, its use is now widely not

advised in the governing standards.

Although the UVA lamps’ lack of higher UV

and longer wavelengths can result in photo-

degradation differences compared to sunlight

for some coating chemistries, the overall

coating industry experience with it has been

good. However, it is rarely used to test high-

performance coatings such as automotive

paint systems. The UV test generally isn’t

considered a true weathering test, but rather

a useful screening tool.

A New Model for Artificial Weathering TestsLaboratory artificial weathering instruments

have various adjustable parameters which

control the spectral and irradiance charac-

teristics of the solar simulation, mode and

quantity of moisture delivery, temperatures

and their cycles. One criticism of artificial

weathering is that correlation to field expo-

sure, such as South Florida, can be lacking,

either universally or for specific coating test

specimens because many of the test cycles

which are used in these devices are inade-

quate. For example, many of the most com-

mon test cycles go back to the carbon arc

heydays of the 1930s and 1940s and are still

used today with xenon, even though they

were never designed to match South Florida.

The situation is gradually improving, however.

A consortium of companies has worked on

developing a xenon arc test method with

greatly improved South Florida correlation

for high-performance automotive and aero-

How to Test the BinderIn coating formulation development, the binder

performance is of primary interest. The binder

fundamentally determines coating perform-

ance and lifetime. This includes mechanical

and other physical properties such as hard-

ness, erosion- and embrittlement-resistance,

and adhesion.

As lower wavelength UV and moisture expo-

sure most commonly affect binder properties,

another laboratory technique alternating expo-

sure to UV fluorescent lamps and moisture

condensation was developed in the 1950s. The

QUV and UVTest instruments are widely used

for high-throughput, low-cost comparative

screening of coating resin formulations.

The test uses one of two types of UV fluo-

rescent lamps. One is the UVB-313 with peak

The Equatorial Mount with Mirrors for Acceleration with Water or EMMAQUA focuses sunlight onto a rackof samples with 10 first-surface reflective mirrors as it tracks the sun across the sky. Water spraysduring the day provide thermal shock.

Over a Decade of Quality Painting Leads

COMMERCIAL PAINTINGLEADS ON DEMAND

Scan this barcode with your smartphonefor a FREE trial

Find work faster with Paint BidTracker, the only lead servicedesigned for the coatings industry. Try it for FREE today, visit www.paintbidtracker.com/trial to claim your 5-day trial.

Contact Howard Booker at hbooker@paintbidtracker.com or1-800-837-8303 x 157.

• Targeted painting leads sent right to your inbox • Searchable database • Plans and specifications

P

48 D+D OCTOBER 2014

space coatings. Their efforts focused on get-

ting an even better sunlight spectral match,

and cycling irradiance levels and specimen

temperatures consistent with Miami daylight.

Further, they based moisture delivery and

timing on actual coating behavior (rates and

cycles of moisture uptake and desorption)

in Miami.

The new test cycle, published in 2013 after

a decade of work, is ASTM D7869 Standard

Practice for Xenon Arc Exposure Test with

Enhanced Light and Water Exposure for

Transportation Coatings. The test serves as

a model of how to develop weathering test

conditions.

In addition to greatly improved South

Florida correlation, the test is 40 percent

more accelerated than the previously

employed test. Although not yet validated for

other coating systems, the standard is being

Hundreds of thousands of paint samples face the weather at a South Florida test site. Some are rela-tively short one- to two-year exposures for evaluating formulations in development. Others are longerfive- to 10-year tests to establish warranty and service life. Some specimens have weathered for morethan 30 years and haven’t yet failed.

Click our Reader e-Card at durabilityanddesign.com/ric

he specializes in the

weather durability testing

of materials and products.

A frequent speaker at

various worldwide techni-

cal symposia, he is the

author of more than 120

Coatings A to Zielnik49

Scan this QR code withyour smartphone to

learn more.

WWW.DURABILITYANDDESIGN.COM

Building Performance & AestheticsOnline • In Print • Daily eNewsletter

A Technology Publishing Co. Product

With the Durability + Design Digital Edition• Content optimized for all smartphones and tablets

• Fully downloadable to Mac or PC desktops and laptops for offline viewing

• Fully searchable and printable

• Articles shareable via email, Facebook, Twitter & Google+

DURABILITY + DESIGN GOES WHERE YOU GO

evaluated by many coatings researchers to

speed product development. It is under the

jurisdiction of ASTM subcommittee D01.27 on

Accelerated Testing.

The Outdoor Test is Always RightThe reality of weather durability testing is

that the outdoor test is always right. Any

accelerated test invariably alters the natural

ratio and cycles of the key weathering

stresses, which can introduce error. Labora-

tory artificial weathering can minimize the

variability of outdoor exposures, but test con-

ditions must be appropriate for both the coat-

ing chemistry and the intent of the test, such

as a match to South Florida results. With the

proper selection of testing technique and

parameters, coatings manufacturers can

increase their confidence in and reliance on

accelerated weathering to make decisions

about coating formulations. Often this

requires a break from past methods. Ulti-

mately, the results of any laboratory test

must be validated with real-world, real-time

exposures.

To help facilitate this, researchers created

the Worldwide Exposure Network to include

major global climates and geographies.

As coatings become more durable and long-

lived, the need for reliable accelerated testing

increases, and new tools and techniques have

already emerged. It’s an exciting time in dura-

bility testing, certainly better than sitting

around watching paint panels slowly weather

on a test fence.

NotesEMMA, EMMAQUA, UA-EMMAQUA, Xenotest,

Weather-Ometer, Fade-Ometer and UVTest

are trademarks of Atlas Material Testing

Technology. QUV is a trademark of Q-Lab

Corporation.

About the Author Allen Zielnik is senior consultant-weathering

science in Atlas Material Testing Technology

LLC’s global Consulting Solutions group, where

publications and conference presentations. He

has degrees in electronics engineering and ana-

lytical chemistry, and since 1994, he has been

involved with natural and accelerated weather-

ing technology and solar simulation with Atlas

Material Testing Technology. D+D

Click our Reader e-Card at durabilityanddesign.com/ric