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Mold & Mildew - Control Studies

For years, mercurial paint preservatives have set the standards regarding performance against mildew growth.

However, in 1995, all US EPA registrations were cancelled for toxicity & environmental concerns.

A four-year exposure study performed by Merck compared three different types of coatings & mildew resistance. The study also compared various levels of Stay-Clean I/E with phenyl mercury compounds.

Paint 1: Control: Non chalking 25% long oil alkyd modified polyvinyl acetate paint. The paint had two coats. Self-primed on white pine siding. The control showed light mildew at six months and moderate to heavy after 15-18 months.

With Additives: Stay-Clean I/E and the phenyl mercury compound exhibit perfect mildew control during the first 12-15 months with trace mold remaining 2.5 years of exposure.

Results: Both Stay-Clean I/E and phenyl mercury showed good mildew control.

Paint 2: Control: Non-chalking 20% long oil alkyd acrylic paint. Two coats self-primed on white pine. After three years - heavy mold developed.

With Additives: Stay-Clean I/E exhibited perfect mildew control for more than three years. Trace mildew was noted after 39 months exposure. Light mildew growth on the phenyl mercury-treated paint was observed at 18-months.

Results: Stay-Clean I/E showed the same good mildew control as phenyl mercury and was superior in all other exposures. Paint 3: Control: Non chalking 15% long oil alkyd acrylic paint. One coat top coat over 15% alkyd paint were applied to edge-grain cedar. Control topcoat was also tested over primers protected with phenyl mercury and Stay-Clean I/E.

Results: Better mold control was observed with Stay-Clean I/E. Equivalent mildew control was observed with primers and topcoats treated with phenyl mercury and Stay-Clean I/E.

Test Organism

MIC (A.I.,ppm)

Yeast and Fungi


Alternaria candidus


Alternaria chevalier


Aspergillus fumigarus


Aspergillus niger


Cladosporium sp


Colletotrichum lindemuthianum


Dacrylium dendroides


Diplodia natalensis


Fusorium roseum


Microsporum audouini


Neurospora sitophilia


Pullularia pullulans


Stadhibotris sp


Tridhoderma viride


Ustilago zeae


Verticillium albo-atrum