Hi John;

Here in Sarasota, everytime I glue a wood project in the garage and incompletely remove the residue with a damp cloth, I get mildew. First noticed it on an oak bookcase many years ago that developed the "black plague" the morning after I clamped and cleaned the excess glue. It also happened on the hull of my stripper one or two evenings after wiping off the excess wood glue that squeezed from the joints.

It has always sanded off with no problem, if I sand it the following day, before it can develop much tooth. There is enough chlorine in our city water supply (about 3-5ppm)where a clean cloth with fresh water will never do this on its own. The glue, or a dirty rag seem to be necessary ingredients.

What I would conclude is that a very small amount of chlorine in the cleaning water is sufficient BEFORE the mildew develops, as is the need for a clean rag and thorough glue removal - If your only glue was epoxy, take a long look at the rags you were using . . . A clean rag, no glue, and trace amounts of chlorine in the water have never produced mildew on one of my "garage projects" - And absolutely everything left outdoors here mildews . . .

FWIW, Spidey