Paints and varnishes - Laboratory method for testing the efficacy of film preservatives in a coating against algae. prEN 15458: 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 a coating against algal growth. It applies only to coatings that are susceptible to algal growth and is intended as preservatives for the film preservation, not for the protection of the substrate itself (e.g. wood).

To determine the algicidal 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 control of the test, to verify that the substrate does not inhibit the growth of algae. 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 onto the solid culture medium in Petri dishes and inoculated with the algae suspension, spreading it evenly over the entire surface of the specimen. The algae suspension used for the test will be a mixture containing one blue-green algae (to be selected between: Nostoc commune and Gloeocapsa atrata Kützing) and one green algae (to be selected between: Klebsormidium flaccidum and Stichococcus bacillaris). The plates are incubated at 23°C ± 2°C, illuminated with a light of 1000 ± 200 lx and a cycle of 16 hours illumination and 8 hours darkness. The growth of the algae in the test specimens is carried out visually macroscopically 14, 21, 28 and 35 days after the inoculation. The maximum duration of the test is 35 days, but it can be finished earlier if the parts treated with the unpreserved test specimens have severe algae growth.

The evaluation of the algal growth on the surface of the specimens treated with the preservative coating is assessed in relation to the growth in the specimens treated with the non-preserved coating. A rating with an index from 0 to 2 is assigned to each specimen treated with the film preservatives. If there is no growth on the surface of the test specimen or in the Petri dish, the growth of the piece will be classified as "0"; if there is less growth in the specimens treated with the film preservatives compared to the non-preserved specimens, it will be classified as "1"; and if there is equal or greater growth in the specimens treated with the film preservatives with respect to the non-preserved specimens, it will be classified as "2". The efficacy of film preservatives in a coating is demonstrated if the samples containing film preservatives are rated "0" or "1".