Paints and varnishes - Laboratory method for testing the efficacy of film preservatives in a coating against fungi. prEN 15457: 2020.

Test not accredited by ENAC (Spanish National Accreditation Entity).

This standard describes a test method to determine the biocidal / biostatic efficacy of active substances or combinations thereof used in film preservatives in coating against fungal growth. It applies only to coatings that are susceptible to fungal growth and is intended as preservatives for film preservation, not for the protection of the substrate, e.g. wood.

To determine the fungicidal efficacy of film preservatives in a coating, the coating material with the test biocide and the coating material without the test biocide are each applied to a substrate strip of filter paper. The coating is applied according to the manufacturer´s recommendations for normal use. Untreated filter paper will also be used as a control of the test, to verify that the substrate does not inhibit the growth of fungi. The samples are conditioned for 5 days at 23ºC ± 2ºC and 50% ± 5% relative humidity. After conditioning, three specimens of each type (containing film preservatives, non-preserved, and untreated), each with a diameter of 55 mm, are obtained and sterilized. The client must select the method of sterilization of the samples, among those available in the laboratory. The test specimens are placed with the coated surface of the test specimen being face up on Petri dishes with culture medium and inoculated with the suspension of fungal spores, spreading it evenly over the entire surface of the specimen. The spore suspension used for the test will be a mixture containing two fungi that grow in exterior environments (to be selected between: Aureobasidium pullulans, Alternaria alternata, Cladosporium cladosporioides, Phoma violaceae and Ulocladium atrum) and two fungi that grow in interior environments (to be selected between: Aspergillus versicolor, Aspergillus niger, Stachybotrys chartarum, Penicillium purpurogenum and Rhodotorula mucilaginosa). The plates are incubated at 24°C ± 2°C, performing macroscopically visual evaluations 7, 14 and 21 days after inoculation to assess the fungicidal efficacy of the film preservatives in the coating. The maximum time of the test is 21 days, but it can be finished earlier if the specimens without preservative show a fungal growth greater than 50% of the surface of the test piece.

Based on the intensity of fungal growth on the surface of each specimen, a rating is assigned to the test specimens with an index from 0 to 4. If there is no growth on the surface of the test specimen, the growth will be classified as "0" ; if there is up to 10% growth on the surface of the test specimen it will be classified as "1"; if there is a growth of more than 10% and up to 30% on the test surface, it is classified with a "2"; if there is a growth of more than 30% and up to 50% on the test surface, it is classified with a "3"; and if there is more than 50% to 100% growth on the surface of the test specimen it is classified with a "4". A film preservative demonstrates efficacy against fungi if the test specimens containing film preservatives are rated less than "4".