NBSIR 83-2781

Performance Criteria for Restoration

Coatings for Porcelain Enamel Surfaces

U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Building Materials Division

Washington, D C. 20234

September 1983

Prepared for Division of Energy, Building Technology and Standards

Department of Housing and Urban Development

Washington, D.C. 20410

"Rf-T.

QC

I A r NBSIR 83-2781 ) 0

PERFORMANCE CRITERIA FOR RESTORATION

COATINGS FOR PORCELAIN ENAMEL SURFACES

James F. Seiler

U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Building Materials Division

Washington, D.C. 20234

and

Paul G. Campbell

Coatings Consultant

Gapland, Md. 21736

September 1983

Prepared for Division of Energy, Building Technology and Standards

Department of Housing and Urban Development

Washington, D.C. 20410

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
.
ABSTRACT

In June 1982, the results of a laboratory-based study to develop interim

performance criteria for restoration coatings for porcelain enamel surfaces

were reported in NBSIR 82-2553, "Development of Interim Performance Criteria

for Restoration Coatings for Porcelain Enamel Surfaces." Additional studies,

consisting of a one-year field test of three of the five restoration coatings

studied in the laboratory, were performed to assess the effectiveness of the

interim performance criteria. The field test included periodic evaluation of

the three restoration coatings applied to a total of nine bathtubs in public

housing units in Alexandria, Virginia.

The results of the field tests were compared to the previous laboratory results

and showed that the interim performance criteria were effective in selecting

durable restoration coatings. This report presents the findings of the field

test and includes the final performance criteria.

iii
TABLE OF CONTENTS

Page

ABSTRACT iii

LIST OF TABLES v LIST OF FIGURES vi

1. INTRODUCTION 1

1.1 BACKGROUND . 1 1.2 OBJECTIVES 1 1.3 SCOPE 1

2. FIELD TEST SITES 2

3. APPLICATION PROCEDURES AND INITIAL TESTING FOR RESTORATION

COATINGS 3

4. FIELD EVALUATION TEST PROCEDURES 5

4.1 ADHESION TESTS 5 4.2 STAIN TESTS 6

4.3 VISUAL INSPECTIONS 6

5. RESULTS OF FIELD TESTS 7

5.1 ADHESION 7 5.2 STAIN TESTS 8

5.3 VISUAL INSPECTIONS 8

6. COMPARISON WITH LABORATORY TEST RESULTS 9

7. PERFORMANCE CRITERIA FOR RESTORATION COATINGS 10

8. CONCLUSIONS 11

9. ACKNOWLEDGMENTS 12

10. BIBLIOGRAPHY 13

APPENDIX A A-l

iv
LIST OF TABLES

Page

Table 1. Data on Field Test Sites 14

Table 2. Stain Resistance of Restoration Coatings Using Four Removal

Methods 15

Table 3. Results of Field Test Visual Examinations of Restoration

Coatings 16

v
LIST OF FIGURES

Page

Figure 1. Typical bathtub with extensive delamination and rusting

before restoration 17

Figure 2. Typical bathtub with decals, dirt and delamination before

restoration 18

Figure 3. Blisters in the bottom of bathtub number 7 19

Figure 4. Typical delaminated blister of restoration coatings 20

Figure 5. Typical pinholing near drain of restoration coatings 21

Figure 6. Typical cigarette stains on restoration coatings 22

Figure 7. Bathtub with non-slip decals 23

vi
1 . INTRODUCTION

1 .1 BACKGROUND

Within the last 15 years, processes have been developed for restoring, in

place, damaged or worn porcelain enamel fixtures such as bathtubs and wash

basins. These processes involve a thorough cleaning (usually by acid etching)

of the porcelain enamel substrate followed by application of an organic coating.

Costwise, these restoration techniques may represent considerable savings when

compared to complete replacement of a damaged or worn porcelain enamel fixture.

In the maintenance of public housing, a continuing problem exists with regard

to porcelain enamel coatings on steel and cast iron fixtures in need of repair.

Performance criteria are needed to aid in ensuring the performance and

durability of restoration coatings.

Previously, a laboratory test study provided the technical bases of interim

performance criteria for restoration coatings for porcelain enamel surfaces! 1] .

1

However, data on the performance and durability of restoration coatings applied

to actual porcelain enamelled fixtures are needed to confirm, or serve as the

bases for modification of, the interim performance criteria.

1.2 OBJECTIVES

The objectives of the research discussed in this report were 1) to assess the

effectiveness of the previously developed interim performance criteria for

restoration coatings for porcelain enamel surfaces using data obtained on coatings applied to actual bathtubs in public housing units and 2) to present

modified performance criteria (if modification was needed).

1.3

SCOPE

In order to meet the stated objectives, a study was performed which involved:

1) the application, by three selected commercial companies, of restoration

coatings to degraded bathtubs in public housing units; 2) periodic evaluation

of the restoration coatings over about a one year period; 3) comparison of the

field study results with the laboratory test results that formed the bases for

the interim performance criteria; and 4) development of performance criteria

based upon both field and laboratory studies.

1 Numbers in brackets refer to references in the Bibliography
2. FIELD TEST SITES

The field sites to study the performance of the restoration coatings on bathtubs were established after consultation with representatives from the

Department of Housing and Urban Development (HUD) and the Alexandria, Virginia

Public Housing Authority. Two sites were selected: the first included three

dwelling units in Cameron Valley, Alexandria, Virginia, and the second included

six dwelling units in Alexandria, Virginia near the Housing Authority Headquarters. Criteria used in selecting specific dwelling units for use in the

study were: 1) the units must be located in the Metropolitan Washington, D.C. area to permit convenient inspection by National Bureau of Standards (NBS) personnel, 2) the units must be among those already identified by the Public

Housing Authority for restoration (this would ensure that the units would be

vacant when initial work was done and would, therefore, not cause disruption

to occupants), 3) the bathtubs of the units must be coated with porcelain enamel

and be in need of refinishing and 4) the units must be occupied following the

restoration and during the evaluation period to permit evaluation of the

effect of in-use conditions on the coatings. The porcelain enamel bathtubs

used in the study were generally cast iron, of various designs and ages. All were basically sound, but exhibited porcelain coatings that were chipped, worn or otherwise degraded. The information on restoration coatings, dwelling

unit location and address, date of refinishing, date of occupancy and occupancy

data are given in table 1.

2
3. APPLICATION PROCEDURES AND INITIAL TESTING FOR RESTORATION COATINGS

The three restoration finish companies were selected for participation in the

field test study because of their previous participation in the laboratory

study [1], Also, they represented a cross-section of performance based upon

previous accelerated laboratory testing results. Company representatives

applied the restoration coatings using their own equipment, materials, and

techniques. Generally, the restoration procedure involved: 1) cleaning the

porcelain enamel coating by etching with a dilute solution of hydrofluoric

acid followed by thorough rinsing (the cleaning was also, in some cases,

supplemented by hand abrasive cleaning); 2) repairing, as needed, chipped areas using a filler; 3) masking the areas not to be coated; 4) thoroughly cleaning

the bathroom to remove dust particles; 5) applying the prime and finish coats

to the dry surface with an air sprayer; 6) curing the coating; and 7) cleaning

up*

The restoration coatings used in the field study were numbered 3, 4, and 5 as described in reference 1. The generic descriptions of the finish coat, as given by the restoration finish companies, were as follows: 3, urethane; 4,

enamel; 5, urethane. Curing times for the coatings were as follows: 24 hour

cure using infrared heat lamps for restoration coating 3; 2 days at ambient

conditions for restoration coating 4; and 7 days at ambient conditions for

restoration coating 5.

Figures 1 and 2 illustrate typical examples of the bathtubs before repair.

Figure 1 shows delamination around the drain area and extensive rusting. Figure

2 shows a bathtub with non-slip decals which have to be removed in the repair

process; also shown are dirt, delamination and loss of gloss.

Only one of the companies used an exhaust system to control dust or to vent

chemical fumes. However, respirators were used by all applicators during

coating application. All companies’ workers used protective gloves during the

etching process. As part of the cleaning operation, all companies used special

care to see that fixtures were removed and that the areas around the drain were clean and dry. All companies took precautions to ensure that the cleaned and

etched porcelain enamel surface was dry and free of dust particles. In addition, plastic covers were used to seal the water outlets to prevent water back

up.

After completion of the restoration process described above, three pull-off

adhesion tests of the restoration coatings were made in each tub. The pneumatic

adhesion test apparatus used was developed at NBS and is described in reference

2. The adhesion tests were made for two reasons: 1) to determine the mode of

failure of the newly applied restoration coatings ? as discussed in Section 4.1

of this report (the modes of faiure prior to occupancy were later compared

to those after occupancy) and 2) to induce three damaged areas similar to

chipped porcelain [approximately 19 mm (0.75 in) diameter] in each tub and

76 mm (3 in) apart. Company representatives then repaired the damaged areas

of each tub using their their own materials and techniques. This provided an opportunity to assess the effectiveness of the processes that would be used to

repair chipped porcelain prior to recoating with an organic coating.

3
Epoxy fillers were used to repair the chipped areas before application of

restoration coatings 3 and 5; fillers were not used in chipped areas of tubs

restored with coating 4.

4
4. FIELD EVALUATION TEST PROCEDURES

Field evaluation tests on the restored bathtubs were performed before and after

occupancy to assess performance attributes described in the interim performance

criteria [1]. Data obtained during occupancy were used to assess degradation

with increased time of exposure under in-service conditions. Adhesion and

stain tests, as well as visual examinations, were used to evaluate performance.

Impact resistance, one of the tests carried out in the laboratory study [1,3]

and included in the interim performance criteria, was not used as an evaluation

method in the field tests because the laboratory data showed that all the organic

coatings tested had greater impact resistance than porcelain enamel. Initial

(before occupancy) adhesion tests were made on July 30, August 13 and September

3, 1981 and adhesion tests after occupancy were made between August 31 and

September 2, 1982. Adhesion tests were not made during intermediate inspections because the test is destructive to the coated surface and repairs were planned only at the completion of the annual inspection to minimize disruption

to occupants. Stain tests were performed prior to occupancy. Visual inspections were made periodically after occupancy, i.e., November 1981 (inspection

no. 1); March 29, 1982 (inspection no. 2), and August 30, 1982 (inspection

no. 3).

4.1 ADHESION TESTS

Adhesion tests were performed near the middle of the bottom of the bathtubs

using the portable pneumatic test apparatus described in reference 2. The

primary elements of the portable test apparatus are a piston assembly, a loading

fixture (stainless steel "button"), a rate of load device to provide a constant

rate of load and a compressed air handling system. A 101.6 mm (4 in) piston

and a 19 mm (0.75 in) load fixture were used. Loading fixtures were bonded to

the coated substrate with an epoxy adhesive. The piston assembly was placed

over the loading fixture and, after attachment, compressed air was steadily

added to the apparatus until rupture occurred. The tensile force required to

induce rupture can be used to provide a measure of coating adhesion if the

rigidity of the substrate is known. As shown in reference 2, the tensile force

at rupture varies with substrate thickness and rigidity. Since the substrate

for the restoration coatings in the bathtubs was more rigid than the steel panel

substrates used in the laboratory tests, the tensile forces obtained in the

field would not be comparable to those obtained on laboratory test specimens.

However, the locus of failure would be expected to be the same in both tests

and provide information on the strength of the restoration coating/porcelain

enamel bond.

After testing, the faces of the 19 mm (0.75 in) diameter loading fixtures

(buttons) and the area of the restoration coating beneath the loading fixtures

were visually examined to determine the dominant failure mode. The failure

modes were defined as follows:

1. At the interface of porcelain and metal substrate

2. In the porcelain

3. At the interface of the primer and porcelain surface

4. At the interface of the primer and finish coat

5
5. At the interface of the loading fixture and adhesive

6. At the interface of the adhesive and the coating surface.

4.2 STAIN TESTS

The refinished bathtubs were rated visually for effectiveness of stain removal

prior to occupancy. Tests were not repeated during or after occupancy

because the laboratory data indicated that stain resistance is not affected by

exposure. The test apparatus, procedures and staining materials, i.e., purple

Tintex, black hair dye, black shoe polish, lipstick, and acetone, were those as described in reference 1. The staining materials selected were those thought

to be in common usage in bathroom areas. The stains were placed upon the

restored bathtub surface using the chambered holders previously described; these

holders prevented stain evaporation or removal during the 16 hour test exposure.

After 16 hours exposure, the stains were removed from the restoration coating

using the following sequence:

method 1 - wipe with soft, dry paper towel

method 2 - wipe with soft, wet paper towel

method 3 - wipe with soft, wet paper towel and mild soap

method 4 - scrub with mild abrasive cleaner

4.3 VISUAL INSPECTIONS

Visual inspections of the restoration coatings on the bathtubs were carried out

to assess the appearance; the data were recorded on an inspection sheet which

contained an individual map of the bathtub, inspection date, code of coatings

defects, and recommendations. The "Pictorial Standards of Coating Defects" [4] was used for guidance for estimating coating defects. While instrumental

measurements of color and gloss changes were not taken of the white bathtubs,

any visual color and gloss changes were noted since they would affect the

overall appearance.

6
5. RESULTS OF FIELD TESTS

5.1 ADHESION

As mentioned in Section 4.1, one reason for performing adhesion tests was to

obtain data on the failure modes. In particular, data were sought on whether

or not the failure mode changed between the time the restoration coatings were applied and the time of the final evaluation, approximately 12 months later.

In the laboratory tests [1], for example, it was observed that, in some cases,

the failure mode gradually changed with increasing time of accelerated exposure,

thus indicating the bond strength between the primer and finish coat to be

degrading.

The adhesion tests prior to occupancy of bathtubs with restoration coating

3 produced rupture primarily either at the interface of the porcelain/metal

substrate or in the porcelain. This indicated that the bond strength of the

newly applied primer and restoration coating was greater than that of the

original porcelain coating. After the 12 month field exposure, the primary

failure mode continued to be either at the interface of the porcelain/metal

substrate or in the porcelain. Thus, after exposure, the adhesion of the

restoration coating system was greater than that of the original porcelain

system.

For bathtubs with restoration coating 4, the adhesion tests prior to occupancy

produced rupture primarily at the interface of the primer and finish coat.

After twelve months, the failure mode was primarily at the interface of the

porcelain and metal substrate. The tests prior to occupancy were performed

three days after application of the restoration coating, even though the restoration company recommended seven days for curing. Testing before the end of

the recommended curing period was required in order to meet the schedule of

occupancy. It is likely that the failures at the interface of the primer and

finish coat were the result of an incomplete curing of the coating system

at the time of testing. It is significant, however, that the tests after

occupancy produced a failure mode primarily at the interface of the porcelain

and metal substrate, indicating that adhesion within the restoration coating

system remained at least as strong as that of the original porcelain system

during the field test.

The adhesion tests, both prior to occupancy and after twelve months, of bathtubs

with restoration coating 5 produced rupture primarily at the interface between

the primer and finish coat.

In the initial tests (prior to occupancy), all three loading fixtures were bonded to each bathtub at the same time. In retrospect, this may not have

been the best procedure, since the energy required to remove a loading fixture

may adversely affect the adhesive bond of the remaining adjacent loading fixtures. In fact, during testing of bathtub number 9 (restoration coating 3), as the first loading fixture ruptured, the adjacent fixture ruptured even though it was not under load or impacted by the loading fixture under test.

For the measurements of the bathtubs after occupancy, adhesion tests were performed one at a time.

7
5.2 STAIN TESTS

The results of the stain test procedures are given in table 2. The wiping and

scrubbing sequence described in Section 4.2 was continued until the stains were either removed completely or were only very lightly visible. The stain

test data obtained on the newly restored bathtubs indicated that the stain

resistance of the field applied coatings was comparable to that measured in

previous laboratory tests [1]. Ordinarily, the hard- to- remove stains would

not be allowed to stand for as long as 16 hours before the occupant would try

to remove the stain; thus, the test procedure is thought to represent a condition more severe than would actually be encountered in service. Despite

this, stains were generally removed after use of a mild abrasive.

5.3 VISUAL INSPECTIONS

Visual inspections of the restored bathtubs were made prior to occupancy and

periodically after the housing units were occupied. Three examinations

(inspection nos. 1, 2, and 3) were made after occupancy and the results documented using inspection sheets as well as photographs to record changes in the

restoration coatings. The results of the inspections are compiled in table 3.

As illustrated in figure 3, tub number 7 had blisters of size 4 to 6 , as defined

in ASTM D 714 [5], covering the entire bottom of the bathtub. Isolated small

blisters were found in at least one tub of each restoration coating. For tub

numbers 3 and 4, blisters greater than 25 mm ( 1 in) diameter were found in the

repaired areas. The blistering did not appear to increase in number or size

after inspection no. 2. The formation of blisters can lead to delamination

as illustrated in figure 4. Pinholing (see figure 5) was observed in inspection nos. 1 and 2 and was prevalent around the drain area. The pinholing may

have been caused by a number of factors including insufficient coating thickness, leaking faucets, or insufficient surface preparation prior to coating

application which was often enhanced by the poor initial surface conditions

(see figure 2). Cigarette stains (burns) were found on the rims of three of

the tubs (see figure 6). Two occupants had added decorative non-slip decals

to their bathtubs (see figure 7). However, most of the restoration coating

companies do not recommend their use. It was observed that some of the decals were delaminated and appeared to be causing minor delamination of the

restoration coating.

Despite the visually detectable problems noted above, the restoration coatings

performed well on all tubs except number 7. Prior to the restoration, tub

number 7 was more heavily corroded than any of the other tubs and it is likely

that the poor initial surface conditions contributed to the observed blistering.

In three instances, the surface of the restoration coating was noted to have

lost some gloss in localized areas. This was likely due to the use of abrasive

cleaning materials.

8
6. COMPARISON WITH LABORATORY TEST RESULTS

In order to develop a final performance criteria document for restoration

coatings for porcelain enamel surfaces from the interim criteria previously

developed [1], an in-service study was essential. Therefore, the laboratorybased performance criteria of appearance, adhesion, impact resistance, stain

resistance and fungal resistance are discussed in the following paragraphs

with regard to their relevance based upon data obtained from the field study.

All the restoration coatings used in the field study met the interim performance

criteria for appearance, which were based upon laboratory test results. Appearance was estimated in the field study by visual examination and documented

using inspection sheets and photographs. Instrumental gloss, reflectance, and

color measurements were not made because of the bulk of the instruments

involved, the lack of flat surfaces required for the measurements, and the

lack of uniformity of cleaning methods used by the occupant. In general, the

bathtubs of the field study retained their color and gloss. However, where

highly abrasive cleaning materials were used, gloss decreased noticeably in

the abraded areas. The loss of gloss appeared to be more dependent on the

occupant's cleaning methods than upon the individual restoration coatings.

Except for tub number 7, the appearance of the coatings was good throughout

the field study. As noted in section 5.3, the blistering and delaminations

on tub number 7 may have resulted from particularly poor surface conditions

prior to restoration.

The modes of failure, as determined by the adhesion tests, were found to be

similar for both field and laboratory tests and the failure modes of two of

the three coating systems indicated the adhesion within the restoration coating

system to be greater than that in the porcelain coating system.

The impact resistance was not measured in the field test for reasons presented

in section 4.0. Only one instance was observed in the field study of chipping

due to impact.

The stain resistances of the coatings in the field study and in the laboratory

study were similar in that typical household staining materials could be removed

nearly completely even though left in contact with the coatings for 16 hours.

The field test was modified slightly from the laboratory test in that a mild

abrasive cleaner was used to aid stain removal. There were cigarette stains

(burns) on the rims of three of the bathtubs. The extent and presence of many

cigarette stains to a bathtub indicated that the stains could not be removed

easily.

In the laboratory fungus resistance test, all restoration coatings met the

requirements of a rating of 10 according to ASTM D 3274 [6]. In the field

test, none of the restoration coatings showed signs of fungal growth after one year exposure. This result was encouraging, as many bathrooms had continually

leaking water fixtures, there were instances of deteriorating plaster adjacent

to the bathtubs, and the cleaning methods of the occupants varied widely. Thus,

the interim performance criterion for fungus resistance appears relevant to

actual field usage of restoration coatings.

9
7. PERFORMANCE CRITERIA FOR RESTORATION COATINGS

The comparison of field test performance with test results according to the

interim performance criteria formed the bases for the final performance criteria

for restoration coatings which are presented in appendix A. The relevance

of the interim criteria is discussed in the following paragraphs.

In our opinion, the criterion for appearance should remain unchanged. The

availability of test instrumentation and standard test panels (both planar

substrate and coatings applied under standard conditions) as well as the adequacy of the interim requirements make changes unnecessary. As reinforcement,

the restoration coatings involved in the field test retained their appearance

after a year's exposure, unless the surfaces were abused or unless the surface

of the tub was badly deteriorated before restoration.

The adhesion tests, of the restoration coatings in the field study, both initial

and after exposure, indicated that the adhesion within the restoration coating

systems was generally good despite visual observation of some blistering.

The blistering was typically localized and may have resulted from inadequate

preparation and badly degraded tub surfaces. Since the failure mode data from

the field test indicated that the adhesion within two of the three restoration

coating systems was at least as great as that of the porcelain/metal substrate,

the interim performance criterion for adhesion appears to be appropriate.

The restoration coatings in the laboratory tests had impact resistance values

higher than unrestored porcelain. The requirement of 0.53 Nm impact resistance

should be adequate for quality assurance.

The stain resistance tests of the restoration coatings in the field study

confirmed their resistance to common household stains as found in the laboratory tests. This indicates that the interim performance criterion for staining

is relevant to field performance and should remain in the final performance

criteria. However, the restoration coatings were not resistant to cigarette

stains (burns). The combination of high temperatures of a burning cigarette

and accumulation of tar residues appears to facilitate penetration into the

organic coating. Because staining by cigarettes can be considered an instance

of abuse and because it is unlikely any organic coating would resist such

stains, a stain resistance requirement for cigarette burns has not been

incorporated into the performance requirements.

The fungal resistance of the restoration coatings used in the field study was excellent in spite of often favorable conditions for fungal growth. Thus, the

test requirement of the interim criteria document appears to be adequate.

10
8. CONCLUSIONS

Conclusions based upon the field study are as follows:

1. Data obtained from the field study indicate that the interim performance

criteria provide an effective assessment tool for restoration coatings.

The restoration coatings that met most or all of the interim performance

requirements also performed well in service on eight of the nine bathtubs

studied.

2. The performance of the restoration coatings after a year of in-service use

was, in general, good. Only one bathtub would have needed complete restoration because of extensive blistering and delamination and the degradation

is believed to have stemmed from the poor condition of the tub prior to

restoration. Other bathtubs needed only spot repairs, if repairs were

needed at all.

3. Surface preparation is a critical factor for the restoration coating process.

For the restoration coating to be applied successfully, not only do the

personnel performing the application need to be skilled, but the areas where the bathtubs are to be coated have to be free of water, dust, dirt,

or other foreign material. Also, adequate working space is required.

Unfortunately, the bathrooms used in the study were cramped, water intrusion was sometimes impossible to control, and it was always extremely

difficult to control dust and dirt because the whole housing unit was

being restored at the same time. The blistering and delaminating that

were likely associated with poor surface conditions prior to restoration

indicate the need for additional information on surface preparation for

badly degraded substrates.

4. The adhesion test apparatus used for the field test proved to be useful in

assessing the failure mode of restoration coatings.

5. The gloss of restoration coatings is likely to be affected by the use of

abrasive cleaning materials. The types of cleansers used were not con- trolled in the field tests and, in three instances, cleaning in localized

areas of the bathtub left an uneven appearance. The problem of surface

dulling by use an abrasive cleaner had been noted in the previous report.

This points out the need to use mild abrasives in cleaning restoration

coatings.

11
9. ACKNOWLEDGMENTS

The authors thank the following NBS staff members: Mr. Larry Masters for

assisting in and guiding the report preparation; Mr. Jack Lee for assisting in

the field study; Mr. Mark Heifer for photography; and Mr. Charles Summers for

fabricating the special test apparatus. Also, we thank Mr. Mel Hockhalter and

his staff at the Alexandria Public Housing Authority for their valuable assistance and Ms. Dorothy Allen of the Department of Housing and Urban Development

for serving as contract monitor for the study.

12
10. BIBLIOGRAPHY

1. Seiler, James F. and Campbell, Paul G., "Development of Interim Performance

Criteria for Restoration Coatings for Porcelain Enamel Surfaces”, NBSIR

82-2553, National Bureau of Standards, June 1982.

2. Seiler, James F., McKnight, Mary E., and Masters, Larry W. , "Development of

a Test Apparatus and Method for Measuring Adhesion of Protective Coatings",

NBSIR 82-2535, National Bureau of Standards, July 1982.

3. "Test for Resistance of Organic Coatings to the Effects of Rapid

Deformation (Impact)", D 2794, ASTM Book of Standards, Part 27, American

Society for Testing and Materials, Philadelphia, PA 19103, 1980.

4. "Pictorial Standards of Coating Defects", Federation of Societies for

Coatings Technology, 1315 Walnut Street, Philadelphia, PA 19107.

5. "Evaluating Degree of Blistering of Paints", D 714, ASTM Book of Standards,

Part 27, American Society for Testing and Materials, Philadelphia, PA,

19103, 1980.

6. "Evaluating Degree of Surface Disfigurement of Paint Films by Fungal

Growth on Soil and Dirt Accumulation", D 3274, ASTM Book of Standards,

Part 27, American Society of Testing and Materials, Philadelphia, PA,

19103, 1980.

13
Table

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Enamel

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NBSIR

82-2553
Table 2. Stain Resistance of Restoration Coatings Using Four Removal Methods 1

Method 1

Company Code

Restoration

Coating

Purple

Tintex

Black

Hair

Dye Acetone

Black

Shoe

Polish Lipstick

3 L D SDS L L

4 L L NE L L

5 VL L SDS VL L

Method 2

3 L D 2/ L L

4 L L 2/ L L

5 VL L 2/ VL L

Method 3

3 VL L 2/ VL VL

4 L L 2/ VL VL

5 VL VL 2/ VL VL

Method 4

3 VL VL 2/ VL VL

4 VL VL 2/ R R

5 VL VL 2/ VL VL

U Method 1 - Wipe with soft, dry paper towel

2 - Wipe with soft, wet paper towel

3 - Wipe with soft, wet paper towel and mild soap

4 - Scrub with mild abrasive cleaner

2J No further treatment

Description of Abbreviations

R - stain removal DC - discolored surface

NR - stain not removed DS - dissolved surface

VL - very light stain remained SDC - slightly discolored surface

L - light stain remained SDS - slightly dissolved surface

D - dark stain remained NE - no effect

15
Table 3. Results of Field Test Visual Examinations of Restoration Coatings

Comments

istoration Coating

and Tub No. Inspection No. 1 Inspection No. 2 Inspection No. 3

3-7 Slight blistering in

bottom of tub; small

pinholes

Extensive blistering;

delamination of blisters;

rust observed beneath

ruptured blisters along

rim of tub

Same as No. 2

3-8 Slight pinhole rusting

around drain (during

application water

backed up into clean

work area and it was difficult to dry

properly around drain

area)

Slight blistering and

delamination of blisters

around drain; pinhold

rusting radiating to ca. 20 cm around drain; chip

in rim to metal by impact;

slight dulling of gloss

Same as No. 2

3-9 Slight rust appearance

around drain area

Slight localized blistering Same as No. 2

4-1 No defects Decals added to bottom of

tub; pinhole rusting near

drain; two slight cracks

along rim

Same as No. 2

4-2 No defects Dulling of gloss and

scratches at bottom of

tub; slight cracks in

bottom of tub; cigarette

stains on rim

Same as No. 2

4-3 Slight pinholing Blistering ca. 30 mm over previous repairs; slight

rusting (near drain)

Same as No. 2

5-4 Slight cracking and

rusting around drain

Decals added to bottom of

tub; slight dulling of

gloss on bottom of tub;

scratches; also 30 mm

blister over repaired area

Same as No. 2

5-5 No defects Slight blistering and

delamination; cigarette

staining on rim

Cigarette staining on

rim; small area of pinholes near drain

5-6 No defects ca. 2 mm ruptured blister Cigarette staining on rim

16
Figure 1. Typical bathtub with extensive delamination and rusting

before restoration

17
Figure 2 Typical bathtub with decals, dirt and delamination before

restoration
I

[% • X J

%

«

3*

Figure 3. Blisters in the bottom of bathtub number 1±!1 /

1J The figure shows an area of approximately 65 cm^ (10 in^).

19
Figure 4. Typical delaminated blister of restoration coatings

20
Figure 5. Typical pinholing near drain of restoration coatings

21
Figure 6. Typical cigarette stains on restoration coatings

22
Figure 7. Bathtub with non-slip decals

23

APPENDIX A

PERFORMANCE CRITERIA FOR RESTORATION COATINGS FOR

PORCELAIN ENAMEL SURFACES
APPENDIX A. PERFORMANCE CRITERIA FOR RESTORATION COATINGS FOR PORCELAIN ENAMEL

SURFACES

A. 1 INTRODUCTION

These performance criteria are applicable to organic coatings used in the

restoration of porcelain enamel surfaces. They are based upon 1) the results

of laboratory tests conducted on five restoration coatings and on specimens of

unrestored porcelain enamel test panels and 2) the results obtained after

approximately one year of actual in-service use of restoration coatings. The

tests and criteria are intended to provide the data needed to assess the

expected in-service performance of restoration coatings from laboratory tests.

The criteria reflect performance characteristics which restoration coatings

would be expected to show in-service; they include appearance, adhesion, impact

resistance, stain resistance, and fungal resistance. Abrasion resistance is

included as part of the cyclic exposure test.

The criteria refer to exposure of porcelain enamel test panels to accelerated

bathtub exposure cycling (ABEC). The cycling includes wet and dry cycling,

elevated water temperature and surface abrasion. In the laboratory study [1], an automatic dishwasher was modified for continuous cycling using water temperatures of 43°C (110°F), air drying temperatures of 77°C (170°F), and detergent

injection at each bath cycle. At the end of 28 bath cycles (24 hours), the

cooled panels were abraded on a Porcelain Enamel Institute (PEI) abrasion

tester for 56 machine counts where the abrasive used was feldspar-containing

cleanser (modified ASTM C 448 test) before repeating the cyle. Thus, one accelerated bathtub exposure cycle (ABEC) included 28 bath cycles and one abrasion cycle.

A. 2 PERFORMANCE CRITERIA

A. 2.1 Appearance

Requirement

When applied at the restoration coating company's designated rate and method,

the restoration coating shall provide a smooth, uniform gloss appearance under

ordinary conditions of illumination and viewing, both initially and after

in-service exposure.

Criterion

When applied to a porcelain enamel test panel using the designated rate and

method, the initial (before exposure) 60° gloss measurements, as described in

ASTM D 523, shall be 75 or greater. The initial apparent reflectivity (white

only) [Directional Reflectance, 45°, 0°] shall be at least 85 as described in

ASTM D 2244. After exposure to 25 ABECs, the 60° gloss in the unabraded area

shall be 70 or greater, and the color difference (E) shall be less than two NBS

units (ASTM D 2244).

A-l
Commentary

Materials for the restoration of porcelain enamel substrates should have initial

gloss and reflectance characteristics similar to those of porcelain enamel.

After exposure to accelerated bathroom exposure cycling, the restoration

coatings should retain both color and gloss.

A. 2. 2 Adhesion

Requirement

The restoration coating shall adhere to a porcelain enamel substrate both

initially and after in-service exposure.

Criterion

The mean stress at rupture value of a minimum of five measurements of the

restoration coating shall be at least 3.1 MPa (450 psi) before exposure, and

shall be at least 1.4 MPa (200 psi) after exposure to 25 ABECs when the adhesion

is measured by a pull-off technique, as described in NBSIR 82-2535.

Commentary

The degree to which restoration coatings adhere to porcelain enamel substrates

is very important, especially after exposure to in-use conditions such as wet

and dry cycling, elevated water temperatures and abrasion.

A. 2. 3 Impact Resistance

Requirement

The restoration coating shall have an impact resistance equal to or greater

than that of the porcelain enamel substrate.

Criterion

The mean impact resistance of a minimum of five measurements of the restoration

coating shall be at least 0.53 Nm (4.7 in lbs) after exposure to 25 ABECs;

impact resistance being measured according to a modified ASTM D 2794 procedure

with a 0.45 kg (1 lb) aluminum cylinder.

Commentary

The minimum impact resistance of 0.53 Nm stated above is the mean value

obtained during testing of unrestored porcelain enamel test panels. All of the

restoration coatings evaluated in generating the data needed as the technical

basis for these criteria had impact resistance values higher than that of the

unrestored porcelain because they were elastomeric.

A2
A. 2. 4 Stain Resistance

Requirement

The restoration coatings shall be resistant to household stains common to

bathroom areas.

Criterion

When Tintex, black hair dye, black shoe polish and lipstick are applied for a 16 hour period to restoration coating panels which had been exposed for 25

ABECs, only a very light stain residue shall remain after scrubbing gently with

warm soapy water (modified ASTM D 1308).

Commentary

These staining materials are among those which would likely be used in a bathroom area. In order to maintain an attractive appearance, the restoration

coating should be easily cleaned if staining materials are spilled on the

coating’s surface.

A. 2. 5 Fungal Resistance

Requirement

The restoration finishes shall be resistant to fungal attack when exposed to

in-use conditions.

Criterion

No fungus growth shall appear on the restoration finish after the 30 day

exposure to the conditions of test method ASTM D 3273 (i.e., a rating of 10

according to ASTM D 3274).

Commentary

It is important that an organic coating used in warm, moist environments be

resistant to fungal growth.
U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

1. PUBLICATION OR

REPORT NO.

2. Performing Organ. Report No. 3. Publication Date

SHEET (See instructions) NBSIR 83-2781 September 1983

4. TITLE AND SUBTITLE

Performance Criteria for Restoration Coatings for Porcelain Enamel Surfaces

5. AUTHOR(S)

James F. Seiler, Paul G. Campbell

6. PERFORMING ORGANIZATION (If joint or other than NBS. see Instructions) 7. Contract/Grant No. national bureau of standards

DEPARTMENT OF COMMERCE 8 . Type of Report & Period Covered

WASHINGTON, D.C. 20234

9.

SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State. ZIP)

10.

SUPPLEMENTARY NOTES

| | Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11.

ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here)

In June 1982, the results of a laboratory-based study to develop interim performance

criteria for restoration coatings for porcelain enamel surfaces were reported in

NBSIR 82-2553, "Development of Interim Performance Criteria for Restoration Coatings

for Porcelain Enamel Surfaces". Additional studies, consisting of a one-year field

test of three of the five restoration coatings studied in the laboratory, were

performed to assess the effectiveness of the interim performance criteria. The field

test included periodic evaluation of the three restoration coatings applied to a total

of nine bathtubs in public housing units in Alexandria, Virginia.

The results of the field tests were compared to the previous laboratory results and

showed that the interim performance criteria were effective in selecting durable

restoration coatings. This report presents the findings of the field test and includes

the final performance criteria.

12.

KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s) Organic coatings; performance criteria; porcelain enamel restoration; restoration

coatings; test methods

13.

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