coating failures 2005-06

8/4/2019 Coating Failures 2005-06

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34 June 2005 CleanerTimes

hy are we talking about paint

failures in this magazine? Many companies

doing pressure washing and waterjetting

also do paint application. They deal with

decks, garages, exteriors of houses, metal

buildings, and for the most part, leave the

large commercial jobs to painting contrac-

tors. Pressurized water is an excellent tool

to clean surfaces and remove old paint and

rust and debris prior to repainting.Historically, the most common cause of

paint failure is the preparation of the surface.

What is a paint failure? When a guarantee is

given, a paint failure must be defined care-

fully. For example, are sags, blisters, peeling,

color change, or cracking to be expected? If

so, how much, if any, can be tolerated?

Let me borrow from Driskos terms:

Afailure of coating is the loss of a coat-

ings function or purpose, i.e. when it no

longer protects the substrate, provides

an attractive appearance, or serves some

other function such as a non-slip. The time

of failure is considered to occur when some

action is needed to restore its properties to

the level necessary to again provide its

intended purpose.

Catastrophic coating failure is very sud-

den, very dramatic, and serious.

A defect is a film or surface flaw, deficien-

cy, or incompleteness that deviates from a

specification or industry-accepted condition.

VIEWPOINT

Coating Failuresby Lydia Frenzel, Ph.D.

W


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CleanerTimes June 2005 35

Degradation is a gradual loss of

coating and/or properties result-

ing from service condition and

weathering.

A premature failure occurs sig-

nificantly before the end of a coat-

ings life expectancy.

The service life of a coating is the

period of time during which a coat-ing provides its intended function.

This time will vary with different

exposures and services.

We typically think of premature

catastrophic coating failures as the

criterion for a warranty. However,

sometimes just the loss of gloss in

an area that is cosmetic is a serious

coating failure, even though it does-

nt affect the protective property

or lifetime. In any event, if the coat-

ing is expected to last 10 years in thatparticular service, you dont want

to have to repaint after six months.

Coatings are made different-

ly for interior or exterior use. Coat-

ings are formulated differently for

wood, concrete, plastic, drywall,

and steel or other metals. Coatings

are made differently for dry, hot

services as compared to damp,

cool surfaces (such as a bathroom).

Proper selection of coating is ex-

tremely important.We can break coating failures

down into problems associated with

the coating itself, problems between

the old coating (or substrate) and the

new coating, problems arising from

improper coating application, and

problems from poor surface prepa-

ration. More and more, power wash-

ing and waterjet cleaning are used

in surface preparation. Incompati-

bilities between coatings or coat-

ings and substrates and improper

coating application cannot be re-

medied by surface preparation.

I am working on my old house

and an old, old rental house. Here

are the problems that I am seeing:

chalking, discoloration, fading, loss

of gloss, adhesion failure, cracking,

organic growth (mildew, mold, and

algae), blistering, delamination,

peeling, flaking, and heavy, sagging

coats. There is nothing extraordi-

nary about this list.

As we work on cleaning surfaces,

stripping paint and putting on new

paint, I know that we have to take spe-

cial precautions around crevices,

areas where water can trap on the sur-

face, sharp edges, edges where bolts

or rivets have been placed (faying sur-faces), and limited access areas. There

are corners that we cant get into

and areas under sinks and tubs that

have been wet for years. Paints will

cut at the sharp edges, so we have to

grind or sand edges. Paints that

cover crevices, water pockets, bolts,

and limited access areas (I am lucky

to get any paint on some of the

places) will fail rapidly by cracking,

blistering, lifting, peeling, or flak-

ing and will allow bad things to hap-

pen under the paint.

The exterior coatings are sub-jected to the suns radiation, tem-

perature changes, and erosion. Some

failures come from causes inherent

to the specific formulation within the

coating itself.

For information circle 221


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Chalking is the formation of loose powder on the

surface to give a dull finish. This normally happens

outside. How fast paint will chalk depends on the

formulation. Often, you can restore the gloss with a

pressure wash. However, if the formulation is not cor-

rect, the chalking will come back. A chalked surface that

has been cleaned with power washing is often considered

satisfactory for a new paint.

Erosion is the gradual loss of paint by wear and

weathering. This can happen inside, for example, when

you scrub on flat latex all the way through to the wall,

or outside. Erosion is a natural process; it is a failure if

it occurs very fast.

Discoloration is a change in the initial color after

application. Usually this is caused by exposure to

chemicals or to heat.

Fading is the reduction of color intensity, usually

by sunlight.

Loss of gloss is often associated with chalking,discoloration, and fading. Loss of gloss is cosmetic.

Mildew defacement (or algae growth) is caused

by growth of organisms. It is not only unsightly, but

could be a health problem. Growth of organisms can

be controlled by using EPA-approved biocides. Cleaner

Times has published articles on cleaning organic

growth. Organic growth normally doesnt affect

coating properties.

Brush marks can occur in coatings that have insuffi-

cient leveling for the wet film to flow together. Areas

with less film thickness will always deteriorate before

areas with greater film thickness.Adhesion failures are very common and can be

catastrophic. Typical failures are blistering, peeling,

and flaking.

Blistering can be caused by painting over salts, using

coatings with water-soluble components, and covering

a coating that is still trying to dry, thereby trapping

little pockets of solvent in the undercoat.

Figure 1


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Figure 1 is an example of heavy wrinkling of paint

that occurred within a month of painting in a bathroom.

Wrinkling can occur if too much thickness is applied

in one coat so that the paint doesnt cure properly. Thispaint is adhering everywhere else, but it appears in

this case that this particular area was not complete-

ly moisture free. The moisture on the substrate distorts

the wet film. The coating will have to be stripped and

recoated. This failure could happen if you were wash-

ing the woodwork or using a pressure washer and

didnt get the surface completely dried.

Blisters can occur where paint has been applied

over salts. Water penetrates the coating and collects at

the salt site. Figure 2 is an example of blisters that have

popped because of moisture penetrating the coating

at salt sites. Pressurized water is one of the surest

ways of getting rid of salts.

Incompatibilities include intercoat adhesion, de-

lamination, or peeling; the top coating attacking thebottom coating; and one coating shrinking/expanding

more than another coating. Limited adhesion and

subsequent peeling can occur when a water-borne

Figure 3



Figure 2


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(latex) coating is applied over smooth oil-based enamel.

This is a very common problem in houses and in commercial

painting of smooth epoxy. The water-borne paint cannot

sufficiently attack the underlying coat to form a bond.

The topcoat shown in Figure 3breaks whenever it is hit,

and can be peeled back from the next coat. This latex

will have to be scraped or washed off, a bonding primer

used, OR the underlying paint has to be roughened,

before a new coating can be applied.Peeling or lifting can also occur when paint is applied

over oil or grease. A paint can crawl away from areas where

there is oil to form fish eyes, little areas of very low film

thickness. In kitchen areas, pressure washing with bicar-

bonate or a good detergent is often the solution to getting

the grease spatter off walls or floors.

As paints get old, cracking or

splitting can occur due to stresses.

When cracking occurs, generally a

path is opened to the substrate.

Cracking occurs in many forms:

checking, alligatoring, intercoat

cracking, and mud cracking. Crack-

ing can lead to flaking, rusting at the

crack, and loss of coating.

The paint failure shown in Figure

4 is common in old houses. It is the

peeling of thick, inflexible paint

from the substrate. Cracking and

flaking paint can also be found on

older steel structures.

Figure 5 shows an example of

failed paint that was applied dir-

ectly over mill scale. If the failure is

limited, the cure is to remove the


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Figure 4

Figure 5


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loose material, clean the surface,

and repaint.

These examples are coatings fail-

ures, but not premature coating fail-

ures. The coatings are approximate-

ly 1020 years old and were not

applied over the best of surface con-

ditions. They had a full life and are

just worn out. The repair for the fail-ures in Figure 4 and Figure 5 is

scraping, mechanical cleaning, or

power washing with glass beads or

soft abrasive to remove the coatings.

Sagging is a common problem.

Sagging is excessive coating applied

so that the weight causes the wet

coating to flow downward to form

sags, runs, or curtains as shown in

Figure 6.

We have just touched the sur-

face on some coatings failures andtheir causes. In 1982, Dr. Drisko

photographed 38 different failures.

You should get a copy of his Naval

Facilities Engineering Services Lab

monograph. And yes, I make liber-

al use of hot water, soap, scrub

brushes, and power washing to get

to the root of the problem.

References:

Richard Drisko, Chapter 12, Coating

Failures in SSPC Good Painting

Practices, Fourth Edition, Volume1, has a very good description of terms

and the types of paint failures for the

general practitioner.

TechData Sheet, Jun 1982, 82-08

Paint Failures-Causes & Remedies

was prepared by Dr. Drisco when he

was at the Naval Civil Engineering Lab

at Port Hueneme. It describes 38 coat-

ings failures with small colored pic-

tures. A single copy can be obtained by

writing Naval Facilities Engineering

Services Lab (NFESC), 1100 23rd Ave,

Port Hueneme CA 93043-4370. Multiple

copies (>10) generally cost a dollar each.

Lydia Frenzel, Ph.D. is executive

director of the Advisory Council. She is

an industry resource and works as a

proactive advocate for emerging tech-

nology. She shares her knowledge and

experience through custom courses, edu-

cational modules, and presentations.

Photos courtesy of Lydia Frenzel. CT



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coating failures 2005-06

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