Metal-deck corrosion: Three case studies - Canon Consulting

Focus on Insulation

Metal-deck corrosion:

Three case studies

A combination of factors was found to have contributed to major,
unpredictable patterns of deck corrosion

by Richard P. Canon, RRC, PE

The roofing industry has exhibited Project No. 1 over an area used to charge batteries
a growing concern in recent months for lift trucks. The rusting was ex-
regarding corrosion of metal decks. The discovery of corrosion of the plained as being related to battery acid
Several recent articles in Professional metal deck was initially made on the fumes, a theory later invalidated. Origi-
Roofing ¹ and NRCA Bulletin 15-91 ² roof of Project No. 1 in 1985, about nally, both occurrences were rational-
have discussed a growing concern in three years after construction, when ized as localized anomalies and not a
the roofing community regarding corro- several new penetrations were cut in source of major concern.
sion of metal decks. During the last two the asphalt built-up roof (BUR). This
years the author's roof consulting firm exposed moderate-to-severe corrosion In 1989, six years after construction,
has investigated three projects that of the deck. This corrosion was initially pieces of decking began falling to the
have experienced severe, premature thought to be dormant and isolated to production floor in various areas of the
corrosion of metal roof decking. Two of active leaks. plant. There were numerous leaks doc-
the decks were primed but not painted, umented in the plant with no logical
and one was galvanized (ASTM A 446 Two years later a small area of cor- pattern. Maintenance personnel also
steel with hot dipped galvanized coat- roded deck was replaced after rust was discovered several rather odd "sink
ing conforming to ASTM A 525, G-60). observed on the bottom of the deck

The roof assembly for each project Figure 1: Project No. 1 Roof Cross Section
is shown in Figures 1, 2, and 3. Table
A summarizes the history and data
regarding each project. All three used
phenolic insulation as part of the sys-
tem. This article will discuss the evi-
dence that a combination of factors
involving the insulation, moisture in
the system and inadequate protection
by the deck treatments may have con-
tributed to deck corrosion in these
three projects.

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TABLE A

Parameter Project No. 1 Project No. 2 Project No. 3
Project location Southeast Michigan
Year constructed Northwest South Carolina Coastal South Carolina
Age at investigation 1987
Roof age at removal 1982 1987 4 Years
Generic membrane Pending 5 Years
7 years 2 Years Mechanically Fastened
CSPE
8 Years 3 Years Office Building
1 layer wood fiber
Aggregate surfaced BUR Ballasted EPDM 2 layers phenolic
Fiberglass
Building Use Plastic Molding Retail Store
Insulation Type One layer phenolic One layer phenolic 3
½ inch wood fiber
Insulation facer Foil over corrugated paper Fiberglass
Number of layers 1 1 1 inch phenolic
1 inch phenolic
Thicknesses 1.4 inch 2.3 inch
None
Unusual Interior None None
Conditions Metal
Metal Metal 20
Deck Type 22 22
Intermediate (B)
Deck Gauge Intermediate (B) Intermediate (B)

Deck configuration

holes" on the roof. The owner was nearly every board joint appeared as a nolic insulation, which has been deter-
concerned and requested an investiga- white line indicating voids at insulation mined to be 23.4 percent (at 90 percent
tion by the author to determine what board joints. The same lines were visi- relative humidity and 68E F)³.
was happening to the roof system, ble on the roof on a frosty morning.
particularly the decking. Dry insulation extracted fromsome
Test cuts and cores confirmed the of the areas we had interpreted to be
The author's first taskwas to deter- observations of the IR survey. Areas of dry were found to contain as little as
mine the extent and severity of the phenolic insulation interpreted to be 1.6 percent MCBW.
corrosion. An infrared (IR) roof mois- wet were very wet. Moisture Content
ture survey indicated at least 6,000 By Weight (MCBW) was measured up The roof membrane had numerous
square feet 2, or 11 percent of the roof, to 1,025 percent. Most wet material was deficiencies, which had resulted in
had wet insulation with varying de- found to contain about 250 percent more than 100 documented leaks since
grees of moisture. The author also ob- MCBW.Compare these values with the occupancy. The author also found
served on an IR camera screen that equilibrium moisture content for phe- evidence from the test cuts that the

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joints in the phenolic foam had been Figure 2: From Project No. 1, severe corrosion of deck, plate, and fastener.
butted, or up to ¼ inches wide, at the
time of construction. They were now the deck. In the most heavily corroded tion interface. When it occurred close
up to 1½ inches wide with an average areas, all surfaces were corroded: enough to the deck, this phenomenon
width of 1 inch. *[WE ESTIMATED THE flange, web, and flute. Numerous gal- could result in a leaching effect.
vanizedinsulation fastener plates were
TOTAL CUMULATIVE AREA WHERE THERE heavily pitted and corroded. After extensive study, the author
concluded that water had entered the
IS NO INSULATION DUE TO OPEN BOARD The author determined that the insulation from four sources:
interior conditions were such that a ! Leakage through the membrane.
JOINTS WAS 2,465 FT2. THIS MEANT vapor retarder would not typically be ! Condensation within the roof in-
THAT ABOUT 5% OF THE INSULATED deemed necessary. Relative humidity
ROOF AREA WAS NOT INSULATED!]* during the heating season is generally sulation.
about 40 percent. The bottom of deck ! Condensation in the areas of wide
This was concluded, by observa- temperature is about 75E F. But since
tion, to be the result of shrinkage (i.e. there was no vapor retarder, condensa- board joints.
due to dimensional instability) of the tion was determined to be a significant
insulation, not improper placement. factor in the corrosion analysis. The It is the author's opinion that the
The author believes the resulting gap reason for this is that during the winter presence of the moisture seems to
could have contributed to the corro- months, the dew point would fall within have resulted in serious, accelerated
sion in two possible ways: the insulation (which is where it should corrosion of the metal deck, possibly
be), and most critically could have because it caused an acid to leach from
! First, as the insulation shrank it occurred, under certain conditions, in the insulation (which will be discussed
placed the membrane under ten- close proximity to the deck-to-insula- later in this article).
sion in the region above the joints.
This may have resulted in water From the IR survey, visual inspec-
infiltration through the membrane
in this region.

! Second, at the wide joints, water
vapor would have been allowed to
rise freely. It thus could have con-
densed in those joints on the un-
derside of the membrane or near
the top of the insulation's
sidewalls. This would have led to
wetting of the edges of the insula-
tion in the wide joints as moisture
dripped from the top of the roof
assembly in those areas.

At the test-cut locations, the author
observed the aluminum foil facer was in
varying states of decomposition. How-
ever, metallurgical and chemical analy-
sis concluded the foil was not a factor
in the corrosion. The foam was typi-
cally crushed, broken, and fractured.
Many of the insulation fasteners in the
test-cut locations had corroded from
0.172 inches diameter down to 0.05"
diameter. Most of these fasteners had
some scaly rust. Corrosion was typi-
cally most severe on the top flange of

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tion of the underside of the deck and Project No. 2 Phenolic insulation with a fiber-
test-cut data, the author projected that glass facer was in contact with the
13 percent of the roof deck would have On September 22, 1989, South deck. In many locations, the facer had
to be removed and replaced. Further, Carolina was visited by a very unpleas- become firmly adhered to the corroded
the author estimated that about 30 ant Hurricane Hugo. The roof on this deck. When the insulation was
percent of the deck would be lightly to project,which is located near the coast, removed, the deck came up with it in
moderately corroded and would require was exposed to some of Hugo's higher strips the width of the flange. The as-
field coating. winds. The ballasted EPDM roof bil- sociation of the fiberglass as a reactant
lowed and was ripped in several places. in the corrosion process has not been
The physical condition of the insu- The owner arranged for emergency fully investigated, but is currently not
lation and the extent of corrosion, how- repairs soon after the hurricane. During felt by the author to be significant.
ever, led the author to recommend a final repairs three months later, exten-
total removal of the roof system to the sive corrosion of the primed deck was The author examined the EPDM
deck. It would then be necessary to observed. After 1,710 square feet of membrane for evidence of factory defi-
replace seriously deteriorated deck and steeldeck had been replaced, with more ciencies or deficient field seams or
to coat moderately corroded deck with replacementanticipated, the author was flashings. No serious problems were
a high-solids epoxy coating system. requested to review the situation and found that could explain the extent of
After this preparation, a new roof sys- provide recommendations. observed corrosion.
tem would be installed.
The author extracted numerous test The owner reported that prior to
During the demolition the author cuts from the roof to observe the deck- Hugo, he had only one persistent leak
found the IR and interior survey tech- ing: several were taken in storm-dam- in the store. There was nothing in the
niques assisted in predicting areas of aged wet areas; most were in areas not history of the roof to indicate that the
corrosion in some areas but were of known to have been damaged during deck was rusting except for some or-
little value in most others. Although Hugo. ange stains observed on the end walls
the process gave the author an indica- immediately after Hugo. Despite the
tion of the problem and assisted in The results were of great concern. disappointing results on Project No. 1
developing a basic magnitude of the Out of nine test cuts, eight had with non-destructive testing to locate
extent of the corrosion, it was not as moderate-to-full penetration rusting of
dependable as he would have hoped. corroded decking, procedures for infra-
Figure 3: Project No. 2 Cross Section red, nuclear and capacitance testing
The final area of demolition was were reviewed.
12,250 square feet or 23 percent of the the decking. The flange was typically
project, compared to an initial estimate much more severely corroded than the Because the roof system was bal-
of 13 percent. The area coated with webs or flute. In the most severe areas lasted EPDM, the author ruled out the
epoxy was 6,250 square feet or 12 per- all surfaces of the deck were seriously
cent. corroded.

The corrosion patterns were
unpredictable. The author found the
severity of corrosion could change
from board to board. In this case, total
removal of the roof to the deck expo-
sure was essential in order to accu-
rately assess the extent of corrosion
and the need for replacement or field
coating. There does not appear to be a
viable non-destructive technique that
would have differentiated accurately
the "good" deck from the "bad" in
such a situation.

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IR camera and capacitance meter. The observe the installation of the new The author concluded there were
moisture readings from a nuclear gauge roof. A total of 14,900 square feet, or four "sources" of the water that en-
were questionable, because the author 17 percent of the roof deck, was re- tered the system and initiated the
got low readings on all test-cut loca- placed and 52,094 square feet or 60 corrosion. In order of significance they
tions except one where the insulation percent, was coated with epoxy. Prior are:
was found to contain 1,980 percent to coating, the deck was carefully pre-
MCBW.Here the nuclear count was 19, pared. The use of epoxy requires appli- ! Condensation on the bottom of the
which is not a high reading for 2 inches cators who are trained in the proper membrane.
of insulation that was found to be techniques for this type of coating.
soaking wet. ! Condensation near the deck-to-insu-
The demolition daily exposed ran- lation interface.
In other test cuts where rust was dom, and extensive, corrosion of the
observed, the foam was found to con- decking that the author would not have ! Condensation at insulation joints.
tain only 3.8 percent to 11.4 percent known about if the roof system had not
MCBW and nuclear counts were all remo ved. To have followed a course ! Leaks prior to Hugo.
only four. Therefore, for ballasted other than total removal of the roof
EPDM, non-destructive testing was system would have been a very seri- ! L~eaks from Hugo damage.
concluded to be of little to no value in ous mistake. Total removal is required
correlating wet insulation to areas of to assure all corroded deck is removed. It was observed by the author that
rusted deck. the corrosion was more severe at damp
During the course of the retrofit, areas compared to very wetareas. The
Visuallysurveying the bottom side the author made several observations. acidity of the insulation was tested in
of the deck was misleading too, be- different locations using a pH meter,
cause only about 5 percent of the deck The foam was heavily damaged and was found to range from 4.3 pH in
exhibited visible pitting. In these areas, from compression failure. The author the very wet insulation to a highly
the moisture contents were found to be believes most of this occurred during acidic 1.6 pH in the damp insulation.
about 1,980 percent. the placement of the ballast. Obvi- (The pH scale is from 0-14, with 0 being
ously, there was also some damage acidic, 7 being neutral and 14 being
An orange stain was visible at nu- done during the repairs. The insulation caustic.)
merous flute lines at end laps in the did not display any instability prob-
deck and the exterior end walls. This lems; i.e., there was no shrinkage. This findinginitiallyseemscontrary
orange stain was found to be rust that There were some areas where perlite to logic, until you consider that the
had been carried to the flutes of the was in contact with the deck adjacent concentration of an acid is diluted as
deck and flowed in the building after to phenolic foam in these locations. In more water is added to it, and thus its
Hugo. The staining was not found to these locations there was no rust under pH is closer to neutral. Therefore,
be a reliable indicator of rusted deck- the perlite but there was severe rust acidity can be affected by the quantity
ing. only inches away under the phenolic. of water present, but perhaps not in
*[ WE ALSO NOTICE LESS CORROSION ways you might expect.
The author saw no option but to
recommend again complete removal of UNDER LOCATIONS WHERE TAPERED EDGE PROJECT NO. 3
the roof system to the deck, for two
reasons:We had to visually inspect the STRIPS WERE INSTALLED OVER THE PHE- The author was recently requested
top surface of the deck for rust, and we NOLIC FOAM. IN THESE CASES , CORRO- to consult on a third project that exhib-
were concerned that the continued SION STARTED AT THE TOE OF THE TA- ited corrosion of the metal deck. This
presence of wet insulation could pose PERED EDGE STRIP. roof was about four years old and the
potential future corrosion problems. deck had a G-60 galvanized coating.
IN ASSESSING THE SOURCE OF THE The insulation consisted of two layers
During the demolition, there was a of 1-inch phenolic foam covered by
full-time observer on site to collect EXTENSIVE CORROSION ON THIS PROJECT half-inch wood-fiber board. As shown
samples, to log and map the demol- WE AGAIN CONCLUDED THE PHENOLIC in Table C, the membrane was a CSPE
ished areas, to take photographs and to mechanically attached system.
FOAM WAS THE CULPRIT . THE BASIC
EQUATION FOR CORROSION WAS:

PHENOLIC FOAM + WATER =
CORROSION ]*

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Leaks were reported soon after half of the board and 33 percent the top flange and was attacking the
occupancy. There were numerous defi- MCBW in the lower half. The top layer base metal. No full-penetration rust
ciencies in the installation of the mem- of the phenolic contained 9.4 percent was observed. *[THE CORROSION OF
brane. The persistence of the leakage MCBW and the bottom layer 6.9 per-
led to initiating a partial replacement cent MCBW. The author believes this THE GALVANIZED COATED DECKING WAS
program with the boundaries for re- stratification of moisture is significant, PREDICTED FROM RESEARCH GATHERED
placement based in large part on the as it indicates moisture accumulation
results of an IR survey. As the replace- related to the drive of moisture from an ON PROJECT NO. 1, BUT NOW IT WAS
CONFIRMED.]* Although the corrosion
Figure 4: Project No. 3 Roof Cross Section was not as severe as on Project 2 (both
were the same vintage foam) there was
ment progressed, it became apparent area of high vapor pressure to an area a basis for serious concern.
that there was significantly more wet of low vapor pressure. Condensation
insulation than the IR had indicated. on the bottom of the CSPE membrane *[ANOTHER INTERESTING OBSERVA-
Also during the replacement, a more was observed by the author at the two
disturbing fact surfaced: The galva- cuts made in wet areas. The galvanized TION WAS MADE WHERE A DECK WELD
nized decking was corroding under the fastener plates were slightly corroded
areas of wet insulation. but all of the screws appeared free of HAD BEEN PAINTED. THIS PROTECTED
rust. The author found a saturated area
The author visited the site on a around the fasteners, which may have THE METAL DECK FROM CORROSION
cold, late winter morning and extracted been an indication of a thermal bridge DESPITE ABUTTING CORROSION ON THE
three exploratory test cuts. Two were in (short circuit) at the screws.
known wet areas (from the IR) and one BARE DECK. IT APPEARED THAT A GOOD
was in an area interpreted to be dry. Upon exposing the galvanized
The moisture profile in the wet area is deck, the author's worst expectations COAT OF PAINT OUT PERFORMED THE
interesting: were confirmed. There was aggressive
! Wood fiber = 356 percent MCBW. corrosion on the deck, primarily at the GALVANIZE .]*
! Top layer phenolic foam = 1,734 joints in the lowest insulation board
and on the deck at the fastener penetra- The extent of the corrosion on this
percent MCBW. tion point. There was also a precipitate project is currently not known pending
! Bottom layer of phenolic foam = on the webs of the deck. The flange of possible demolition of the system
the deck was corroded, but there was (which the author has recommended).
551 percent MCBW. little to no corrosion on the web or the The author does not anticipate there
The equilibrium moisture content of bottom of the flute. This has been a will be much if any deck replacement,
the wood fiber is 15 percent and of common phenomenon observed on the but does expect a significant area will
phenolic is 23.4 percent, so these three projects. have to be field-coated.
insulation samples were very wet.
The corrosion had progressed all On this project there had been no
On the dry test cut, the wood fiber the way through the G-60 coating on firm determination at this time of the
was 51 percent MCBW in the upper source of the water that triggered the
corrosion, but the following are our
prime candidates:

! Condensation on the bottom of the
billowed membrane during positive-
pressure operation of the HVAC sys-
tem.

! Condensation within the roof as-
sembly with a fluctuating dew-point
location.

! Top-side leakage through membrane
deficiencies.

! Damage to the membrane from other
trades.

The author has recommended the

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Metal Decks: More than a place to hang your roof

On each of the projects described in the accompanying designed to transfer wind loads (shear loads) through a
article, the metal deck was designed as more than just a diaphragm, the wind load is transferred from the windward
platform for the roof. The deck in such a design serves wall to the roof deck and out to the walls parallel to the
three primary functions: wind direction.

! Supporting vertical dead and live loads. This transfer is accomplished by attaching the deck to the
structuralsupports (joists or beams) with welds or screws.
! Providing a wind uplift resistance component. If the decking has either rusted away from the fasteners or
has corroded to the point it is no longer a monolithic plate
! Providing resistance to lateral (sideways) wind loads capable of distributing loads (a diaphragm), the structure
striking the building. This is referred to as diaphragm could receive extensive damage or possibly rack or
action. collapseduring a wind that is within the structure's design
load, or even less.
When a steel roof deckis seriously corroded, its capacity
to resist these loads is compromised. The deck may no Note: The assessment of loss of structural integrity
longer be capable of supporting snow loads, the dead should be made by a structural engineer who is knowl-
load of the roof system, foot traffic, etc. The wind resis- edgeable regarding deck corrosion and its effects.
tance for an adhered system and a mechanically attached
system are provide by screwing the insulation or mem- As a critical component of such structures, metal roof
brane to the metal deck. decks are anticipated in the design to serve the life of the
building - which in most cases is 50, 75, or even 100 years.
If, for example, 50 percent of the deck has turned to A building owner may expect to have to replace localized
*[CRUSTED]* rust, the uplift resistance of its attachment to areas of rusted deck when he replaces his roof, but should
joists or beams - and the pull-out resistance of insulation not expect to replace his entire roof deck, or large portions
fasteners - is reduced proportionately to the reduction of of it when doing so.
metal thickness. When wind strikes a building that was

inclusion of an air retarder or a change of INVETECH, Houston, Texas in ana- "It is considered axiomatic that
to a fully adhered system in the re- lyzing the chemical reactions related to water will find its way into a roofing
placement to reduce or eliminate any the corrosion process. Product litera- system, either due to leaks or to con-
problems with the HVAC positive pres- ture and his research indicated that the densation. Water absorption by the
sure. phenolic foam contained an aromatic phenolic foam can be extremely high.
sulfonic acid as a catalyst used to cre- The water dissolves the sulfonic acid,
Chemical Analysis ate the cells of the foam. forming an acidic environment which
contacts the roof decking. The organic
What is going on in the roof sys- Slater found that the deck primer materials used to coat the deck (primer)
tem to propagate such aggressive was a purely organic coating. Chloride and protectfromatmosphericcorrosion
corrosion in such a short time? The was present in the corrosion product are unable to withstand these acidic
common denominators in these pro- with 0.001 percent to 0.01 percent by environments and quickly break down.
jects were phenolic foam insulation in weight. Sulfur content, on the other
contactwith a metal deck and the pres- hand, was found to be in the range of Accelerated corrosion of the bare
ence of water *[MOISTURE]*. 0.01 percent to 0.24 percent by weight steel ensues. While it is acknowledged
(i.e., from 10 to 200 times more sulfur that the available quantity ofacidity in
During the author's investigation of than chloride). a given volume of the foam is limited,
Projects 1 and 2 he worked with a and thus cannot by itself sustain accel-
metallurgist/chemist, Dr. John E. Slater Slater's report stated:

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erated corrosion indefinitely, the salts OF THE ROOF ON PROJECT NO. 1 WHICH COMPOSITION OF PHENOLIC FOAM (NOT
produced during the initial corrosion
process will remain within the corro- WAS EIGHT YEARS OLD AT REPLACEMENT THE FACERS OR AN INCREASE IN THE
sion product (rust), rendering its con-
ductivity high. Thus, continued high AND ON PROJECT NO. 2 WHICH WAS TWO COMPRESSIVE STRENGTH), WE HAVE NO
corrosion rates occur in the presence of YEARS OLD, THE ACTUAL CORROSION
moisture trapped in the foam and atmo- RATE WAS 3.5 TO 14 MILS PER YEAR ASSURANCE THAT THE PRESENCE OF
spheric oxygen. The sulfonic acids (0.0295" ÷ 8 YEARS = 3.6 MILS PER YEAR
released by moisture from the phenolic AND 0.0295" ÷ 2 YEARS = 15 MILS PER PHENOLIC FOAM ON A PRIMED OR GAL-
foam therefore act as both an initiator YEAR). THIS IS HARDLY AN ACCEPTABLE
of corrosion and as a catalyst for fur- CONDITION.]* VANIZED DECK WILL NOT CORRODE THE
ther corrosion."
Recommendations DECK.]*
Regarding the use of galvanized
decking, Slater's report states: What can be done to avoid or mini- The author believes that his inves-
mize deck corrosion under the condi- tigation on these projects has raised
"It has been suggested that galva- tions described in these case studies? certain points that require further
nized decking is more resistant to at- The author suggests these as possible study and discussion within the roof-
mospheric corrosion and hence more preventative steps: ing industry.
resistant to the type of attack found on
the (investigated) roof. The corrosion *[! ISOLATE PHENOLIC FOAM FROM First, more designers and contrac-
rate test data clearly indicate that the tors should be aware that phenolic
galvanizing cannot be relied upon to METAL DECK WITH A SEPARATOR foam insulation is vapor-permeable
protect against the sulfonic acid attack. BOARD and therefore capable of absorbing
Furthermore, the sulfonates can be water. This has ramifications relative
anticipated to catalyze atmospheric ! INSTALL A " PERFECT " ROOF THAT to: material storage (that is, stored in a
corrosion of the galvanized layer which place with low humidity); possible in-
remains after the initial acid attack, in HAS NOT NOR WILL LEAK DURING ITS clusion of a vapor retarder in situa-
the same way as for the ungalvanized tions not normally requiring one; ap-
steel. *[THUS GALVANIZING IS NOT CON- LIFE (NOT A PRACTICAL plication of this insulation during hot,
SIDERED TO BE THE PROTECTIVE COAT - EXPECTATION)]* humid weather, and design consider-
ING OF CHOICE IN THIS APPLICATION.]*" ations due to the additional weight of
! Use epoxy coating or equivalent absorbed moisture.
*[TESTS WHICH WERE CONDUCTED applied to prime-coated metal
deck. The industry also needs a better
AND REPORTED BY A PHENOLIC FOAM method to determine the absorption
! Use G-90 galvanize coating, not G- potential of phenolic insulation.
MANUFACTURER STATED THE FOLLOW - 60, for longer resistance to corro- ASTM C1126 is the "Standard Specifi-
ING: sion. cation for Faced or Unfaced Rigid Cel-
lular Phenolic Thermal Insulation."
"UNDER THE MOST SEVERE POSSIBLE *[! H A V E T H E I N S U L A T I O N This standard refers to ASTM C209,
TEST EXPOSURES , I.E. UNPROTECTED MANUFACTURER WARRANT DAM- which includes a moisture absorption
STEEL, ACCELERATED TEST CONDITIONS, test. This test does not adequately
AND CONTINUOUSLY WET (PHENOLIC AGE TO DECK FROM CORROSION model the conditions to which a roof
FOAM) INSULATION, MEASURED CORRO- insulation will be exposed. The test
SION RATES WERE BELOW 2 (1.8) MILS FOR "X" YEARS measures the percentage water ab-
PER YEAR AFTER 200 DAYS ......" sorption increase by volume with a
! USE A ROOF SYSTEM THAT IS EASY two-hour immersion. For one manu-
THE THICKNESS OF 22 GAUGE PRIMED TO VISUALLY INSPECT FOR PHYSI- facturer, this was 2.0 percent by
METAL DECKING IS ABOUT 0.0295" volume. With a density of the foam of
THICK. IF WE CAN EXPECT CORROSION TO CAL DAMAGE 2.7 pounds per cubic foot that is 46
REMOVE 2 MILS (0.002") PER YEAR, THE percent MCBW. Further, immersion
ANTICIPATED DECK LIFE WILL BE ONLY 15 ! USE STAINLESS STEEL SCREWS does not model a vapor drive to which
YEARS! BASED ON OUR OBSERVATIONS in-service insulation is exposed. *[THE
! CONSIDER USING ANOTHER INSULA- INDUSTRY NEEDS A BETTER TEST.]*

TION *[This leads us then to a second

UNLESS THERE HAS BEEN OR WILL

BE A MAJOR CHANGE IN THE CHEMICAL

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point. The industry must acknowledge try needs to know what the deck MCBW.) NEXT REMOVE THE FOAM
that phenolic foam is not "closed-cell" manufactures can and will provide to FROM THE CONTAINER. PLACE A FEW
relative t o moisture. When the prod- the end user. *[THE STEEL DECK INSTI-
uct can absorb 46% in two hours and SMALL STRIPS OF METAL DECKING IN
ultimately nearly 2,000% MCBW, it TUTE RECOMMENDS FIELD PAINTING THE THE SOAK WATER AND MONITOR FOR A
ain't closed-cell! This is important dur-
ing the design stage. Structural engi- DECK BECAUSE THEY SAY THE FACTORY WEEK OR SO. WE OBSERVED RUST ON
neers base their designs and size
structural members on the assumption PRIMER I S "AN IMPERMANENT AND THE EXPOSED CUT EDGES OF THE STRIPS
that the insulation is dry and will re- PROVISIONAL COATING." WOULD IT BE
main dry, not that someday iwt meiagyh 20 POSSIBLE OR PRACTICAL FOR THE MET - IN ABOUT 48 HOURS. WHEN WE
times more than they were told it AL DECK SUPPLIER TO FURNISH A PRE- CHECKED THE PH AFTER THE METAL
would. Mechanical engineers base
their heating and cooling loads on dry PAINTED PRODUCT WITH MORE THAN A HAD BEEN IN THE SOLUTION FOR A
material with a stated "R" value, not a
depreciated, lower value as a result of "PROVISIONAL COATING"? IF NOT, THEN WEEK, WE FOUND THE PH HAD RISEN
moisture absorption. These are impor- THE CHOICES ARE: A G-90 GALVANIZED DUE TO THE CHEMICAL REACTION TAK-
tant liabilities that must considered.]* COATING; AN ALUMINUM ZINC ALLOY ING PACE IN THE CORROSION PROCESS.
COATING; A FIELD APPLIED PAINT OR
In addition, the matter of positive COATING; OR CHANGING TO ANOTHER MORE SOPHISTICATED TESTS CAN
pressure from an HVAC system billow- DECKING SYSTEM.
ing a single-ply membrane is a situa- BE RUN BUT WE HAVE FOUND THESE
tion that is not receiving adequate WHAT CAN YOU DO?
attention from manufactures, design- SIMPLE TESTS ARE QUITE INFORMATIVE.
ers, or contractors. The requirement DURING OUR INVESTIGATIONS WE YOU MAY WANT TO RUN SIMILAR TEST
for roof pressure relief valves, air re-
tarders or fully adhered systems needs HAVE CONDUCTED A SIMPLE TEST TO ON OTHER INSULATIONS FOR YOUR
further study and consideration in the
design process. With the exception of MONITOR PHENOLIC FOAM CORROSION INFORMATION.
only a few manufacturers, air infiltra-
tion remains a non-issue. PROPERTIES AND MOISTURE ABSORP- FOR THOSE WHO HAVE IN-PLACE
TION. YOU MAY WANT TO PERFORM PHENOLIC FOAM, IT MAY BE PRUDENT TO
Regardless of the type of insula- YOUR OWN TESTS TO SEE WHAT HAP -
tion to be used, there needs to be a PENS WHEN A 2" CUBE OF DRY PHENOLIC DETERMINE IF A PROBLEM CURRENTLY
thorough, industry wide review of FOAM IS PLACED IN ABOUT 150 ML OF
metal decks and corrosion. The indus- DISTILLED WATER. EVERY 24 HOUR PE- EXISTS AND THEN RECHECK OCCASION-
RIOD MEASURE THE PH WITH INDICATOR ALLY. TAKE A FEW EXPLORATORY TEST
PAPER OR A P H METER. ALSO CUTS AND SEE IF THERE IS A PROBLEM.
ACCURATELY WEIGH THE SAMPLES . WE ON OUR PROJECT NO. 1, 35% OF THE
FOUND THE PH DROPPED FROM 6.6 TO
3.3 IN ONLY 48 HOURS. THE MCBW IN- DECK HAD TO BE EITHER REPLACED OR
CREASED TO OVER 200% IN THE SAME
TIME PERIOD. (THAT IS FIVE TIMES THE COATED AFTER ONLY EIGHT YEARS. ON
TWO-HOUR IMMERSION VALUE OF 47% PROJECT NO. 2, 77% HAD TO BE RE-

PLACED OR COATED AFTER ONLY TWO

YEAR S . TIME MAY BE YOUR ENEMY IF
THE DECK IS CORRODING. DAMAGE MAY

BE MINIMIZED IF CAUGHT EARLY

ENOUGH.]*

BY THE TIME RUST IS OBSERVED ON THE BOTTOM SIDE OF THE DECK IT IS TOO LATE. THE CORROSION
HAS PROGRESSED TO A POINT OF COMPONENT FAILURE.

* READER NOTE: The text enclosed by asterisks and brackets *[ IN SMALL CAPS ]* was in the author’s original manu-
script, but omitted in the published article by the Editor.

References

1. Professional Roofing: March 1991, NRCA News, Page 63, Tech Transfer, Page 74; April 1991, Tech Transfer, Page 86.
2. "Corrosion Protection For New Steel Roof Decks," NRCA Bulletin 15-91, May 1991.
3. Cash, C. G., "Moisture and Built-Up Roofing," Proceedings of the Second International Symposium on Roofing Tech-

nology, NRCA, 1985, Pages 416-427.
About the Author: Richard P. Canon, a Registered Roof Consultant (RRC) and Professional Engineer (PE), is owner of Canon
Consulting & Engineering Co.,Inc. 1617 John B. White Sr., Blvd., P. O. Box 17007, Spartanburg, SC 29301-0101, (864) 574-6500.

Professional Roofing (Reprinted with Permission. See Note to Reader at end of Article) August 1992
Page 9 of 10
Compliments of Canon Consulting & Engineering Co., Inc.
Spartanburg, South Carolina
(864) 574-6500

ADDITIONAL PHOTOGRAPHS OF MISCELLANEOUS PROJECTS

Figure 5: Project 1, view of wet insulation. Figure 6: Project 1 interior view of corrosion

File: C:\DICK'S FILES\Phenolic\PHENOLIC ARTICLE- 1992.wpd [February 12, 2001(10:17PM)]

Professional Roofing (Reprinted with Permission. See Note to Reader at end of Article) August 1992
Page 10 of 10
Compliments of Canon Consulting & Engineering Co., Inc.
Spartanburg, South Carolina
(864) 574-6500