NATIONAL BUREAU OF STANDARDS REPORT

7382

Investigation of Fungus-Resistance Tests

for Shower Pan Materials

by

Selden D. Cole

and

Paul R. Achenbach

Report to

1 Federal Housing Administration

Washington^ D.C.

<0>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

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NATIONAL BUREAU OF STANDARDS REPORT

Investigation of Fungus-Resistance Tests

for Shower Pan Materials

fey

Selden D. Cole and Paul R. Achenbach

Mechanical Systems Section

Building Research Division

to

Federal Housing Administration

Washington^ D.C.

NBS PROJECT NBS REPORT

NBS Project

1003 - 30-10630

November 17 , 1961 NBS Repo rt

7382

ft

IMPORTANT NOTICE

NATIONAL BUREAU OF S’ intended for use within the

to additional evaluation and

listing of this Report, either

the Office of the Director, N however, by the Governmenl

to reproduce additional copi

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

progress accounting documents

rmally published it is subjected

, reproduction, or open-literature

ision is obtained in writing from Such permission is not needed,

prepared if that agency wishes

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
Apparatus, Culture Medium, and Test Fungi

The apparatus, culture medium, and test fungi used for

these tests were as follows:

(a) The autoclave was capable of maintaining an exhaust

temperature of 121 ± 2°C (249.8 ± 3*6°F) at a pressure

of 15 lbs/sq in. for sterilizing of the culture medium

and the glassware.

(b) The Petri dishes used for qualitative tests were 10 cm.

in diameter.

(c) A sterile room is desirable, but was not available for

these tests. The tests were performed in an isolated

one-room building with a low dust content.

(d) The- incubation chambers were Petri dishes with,

plastic, covets, and maintained at a temperature between

75 °F and 80°F.

(e) The culture medium consisted of:

NH3 N03 on « 0 grams

KH2 P04 2.5 grams

K2HP04 2.0 grams

MgS04 . 7H2 0 2.0 grams

Agar 20 grams

Distilled water to make 1000 ml.

The pH of the medium was adjusted to the range 6.4 to

6.8 with HCJ£ orNaOH as required. The medium was sterilized in' Petri dishes*

(f) The first fungus used was Ghaetomium globosum, A.T.C.C.

6205.

(g) The second fungus used was Aspergillus niger, A.T.C.C.

6275.

(h) Subcultures were prepared in sterilized Petri dishes,

and the inoculum was prepared from the ripe-fruiting

subcultures. The spores were transferred with a sterilized nichrome wire loop, to an Erlenmeyer flask containing about 5 glass beads 1/4 inch in diameter, and

10 ml of distilled water. The mixture was shaken to

break up the spores and then diluted to 200 ml. The

- 2 -
Chaetomium globosum subculture was prepared on Whatman

filter paper placed on the hardened agar. The Aspergillus nlger subculture was similarly prepared except

that 30 grams of brown sugar was added to the 1000 ml

of culture medium before sterilization and hardening.

Test Procedure

Specimens, 1 1/2 inches square, were cut from the shower pan

samples and from a 3/l6-inch thick cement asbestos board.

Pour specimens of each sample were used with each mold inoculum unless it was obvious that both sides of a sample were

the same material. Under aseptic conditions, one half of the

specimens were separately dipped in JO percent ethanol for a few

seconds, rinsed thoroughly in distilled water, and placed firmly

on the solidified agar medium previously prepared in the 10 cm

Petri dishes. A narrow strip of sterile filter paper was placed

in each dish at the same time but at a maximum distance from the

specimen. With a sterile pipette, approximately 1 1/2 ml of

inoculum was distributed over the surface of each specimen, filter paper, and medium in each dish as it was prepared. Each

Petri dish contained a strip of Whatman filter paper as a control, but in addition a control dish of filter paper on medium

was prepared for each mold. The other half of the specimens

were placed on the agar medium in the Petri dishes and inoculated

in the same manner without being previously dipped in ethanol

and rinsed.

The covered Petri dishes were incubated for about two weeks

at a temperature between 75° and 80°F in a room with uncontrolled

humidity.

Test Results

At the end of the incubation period the following results

were observed:

-3-
Table 1

Chaetomium Globosum Inoculation

Specimen Ethanol-Treated

Copper foil-paper laminate

Foil up No specimen

Paper up Mold-covered

Four-layer paper laminate,

with thin plastic coating

on one side

Plastic up Mold at edges only

Paper up Mold-covered

Polyvinyl chloride sheet

(green;

Polyvinylidene chloride

sheet (black)

Polyethylene paper

laminate (2 layers)

Plastic up

Paper up

Few specks on surface

No growth

Edges only

Mold-covered

Filter paper control and

filter paper strips Mold-covered

Cement asbestos board No growth

Untreated

No growth

Mold-covered

Mold at edges only

Mold-covered

Few specks on surface

No growth

Edges only

Mold-covered

No specimen

No specimen

Table 2

Aspergillus Niger Inoculation

Specimen Ethanol -Treated Untreated

Copper foil-paper laminate

Foil up

Paper up

No specimen

Mold-covered

Some growth at

edges

Mold-covered

Four-layer paper laminate,

plastic surface one side

Plastic up Some growth at edges Some growth at edges

Paper up Mold-covered Mold-covered

Polyvinvl chloride sheet Some growth on Trace of growth

(green) medium flowed

thin sheet

onto on soiled spots

-4-
Table 2 ( contd.

)

Specimen Ethanol -Treated Untreated

Polyvinylidene chloride

sheet (black)

Mold specks on

stained spots

Trace of growth on

uncleaned surface

Polyethylene paper

laminate (2 layers)

Plastic up

Paper up

Edges only

Some growth

Edges only

Nearly moldcovered

Control with filter paper

strips Excellent growth No specimen

Cement asbestos board No growth No specimen

The results in Tables 1 and 2 indicate that the paper components in all shower pan materials became mold-covered during

the incubation period of about two weeks when inoculated with

either of the two fungi, the plastic materials showed no mold

growth in some cases and a few specks or a trace of growth in

other cases, and the metal and cement-asbestos specimens showed

no mold growth. The polyvinylidene chloride sheet was slightly

susceptible to growth of Aspergillus niger but not to Ohaetomium

globosum, and the paper component of the polyethylene-paper

laminate appeared to be somewhat more susceptible to growth of

Chaetomium globosum than to Aspergillus niger. The polyvinyl

chloride sheets showed specks or traces of both types of mold

after two weeks incubation and a fairly general, though not dense,

mold growth after seven weeks incubation. The other materials

showed no significant change between two and seven weeks incubaIn general, there was little observable difference in the

amount of mold on the treated and untreated specimens at the

end of the incubation period. There was slightly more growth

of ABpergillus niger on the untreated specimens than on the

treated specimens of polyvinylidene chloride and on the paper

side of the polyethylene-paper laminate.

There was some tendency for the mold growth on the culture

medium to overlap the edges of the thinner laminates even when

the center of the exposed surface showed no visible mold growth.

tion.

-5 -
Discussion and Conclusions:

The fungus-resistance test described in this report is not

difficult to perform, once the apparatus and materials have been

assembled.

A covered Petri dish is adequate as an incubation chamber

for small specimens, and provides a convenient method for maintaining interior conditions at near saturation.

The culture medium described in this report is not critical with respect to the proportions of the ingredients, as

several salt-agar media are known to support mold growth for

pH values up to 6.8. Aspergillus niger propagates better if

brown sugar is added to the culture medium in the proportions

indicated. The use of a sterilized metal loop for transferring

the spores of the subculture and glass beads for forcing the

spores into suspension appears to be preferable to a camel’ shair brush for these purposes especially from the standpoint of

ease in sterilization.

Preconditioning the specimens by dipping in ethanol prior

to inoculation is desirable to minimize the presence of extraneous matter on the surfaces of the specimens. The preconditioning at 250°P specified for duct specimens would not be

satisfactory for shower pan materials, especially those employing plastics.

Recommendations

It is recommended that materials which become generally

coverdd with either Chaetomium globosum or Aspergillus niger

during a 4-week incubation period with the test procedure described herein, be considered to have inadequate fungus resistance. Materials with no mold growth or which reveal a few

specks of mold in an irregular pattern after four weeks incubation should be considered to have acceptable fungus resistance. These requirements should be applied to both sides of

a laminated material, but not to the cut edges.

The reasons for recommending that the fungus-resistance

requirement be made applicable to both sides of shower pan

materials are as follows. The BRAB Task Group that considered

the essential criteria for ducts believed that heating and air

conditioning ducts should be tested for mold growth. It is

difficult to argue that the exposure of ducts to mold growth

would be more severe than the bottom side of a shower pan in

crawl spaces. It seems probable that the criteria, other.rtajian

-6 -
the fungus resistance test, recommended for shower pans will

permit paper laminates with non-cellulosic materials on the

upper side, and that such laminates will be offered in the

future. Since this investigation of mold growth on a number

of laminate's • showed that cellulosic materials invariably supported good' mold go^th and thbt a very thin layer of some

plastic materials would prevent mold growth on paper laminates,

and since the cost of adding such a plastic covering to the

under side of such materials would be quite small, it is believed that the fungus resistance test should be a requirement

on both sides of all materials.

It is recommended that photographs of the specimens, taken

at the end of the 4-week incubation period, be required as a part of the test report on fungus resistance. Each photograph

should be taken with a scale laid beside the specimen to indicate its size, and the light conditions should be such that the

photograph reveals the nature and height of the fungus growth

on the surface of the material. The photograph should be enlarged so the specimen will be of a 6x6-inch size in the enlargement .

USCOMM-NBS-DC

- 7-

II. S. DEPARTMENT OF COMMERCE

Luther H. Hodges, Secictary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director

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