OBJECTIVE:
To evaluate 4 customer prepared solvent based stain samples for resistance
to fungal defacement in accordance with ASTM D5590-94 entitled "Determining
the Resistance of Paint films and Related Coatings to Fungal Defacement
by Accelerated Four-Week Agar Plate Assay"
CONCLUSION:
Samples B, C and D were more than adequately protected against fungal
defacement when tested in accordance with ASTM D5590-94. Sample A, however,
failed to provide fungal resistance.
DISCUSSION:
The results for the fungal resistance evaluation are presented in Table
I. A fungal growth rating of "0" corresponds to the complete absence
of surface growth and a rating of "10" corresponds to complete coverage
of the surface by fungal growth. A rating of "3" of less generally indicates
that the coating should be resistant to fungus under actual use conditions.
The lower growth ratings normally correspond to longer time periods
of fungus free surface under actual use conditions. Leached samples
showing a significant decrease in efficacy (increase in growth rating)
versus the corresponding unleached sample indicate that the biocide
is leaching from the coating to some extent.
EXPERIMENTAL:
Four Week Agar Plate Test (Fungal Resistance)
The samples were prepared for fugal evaluation by dip coating wooden
blocks with each sample in quadruplicate. The blocks were air dried
for 24 hours. Two blocks form each set were leached with distilled water
in one gallon containers at a flow rate of six changes per day for 24
hours and dried again, while the other set remained unleached. The blocks
were then placed on the surface of solidified malt agar plates. One
square from each sample thus prepared was then inoculated with a mixed
spore suspension of Aspergillus Niger (ATCC 6275) and Penicillium funiculosum
(ATCC 11797), and another square inoculated with homogenate of Aureobasidium
Pullulans (ATCC 9348). All plates were incubated at 28° C under
85-90% relative humidity for four weeks. Observations of growth were
recorded weekly.
- John McCloskey
- Microbiologist
- Industrial-Biocides-Technology
N.B. Ref. 382-108
