How do historic Gettysburg homes get mold?

They get it from stone and brick that wick moisture, from plaster that stays cold, from crawls without a vapor strategy, and from modern living — showers, air conditioning, insulation — added to a shell that used to dry by being drafty. Spring rain and winter condensation do the rest.

The fix is not to wrap the house in vinyl paint. It is to keep liquid water out, keep humidity in season, and remove only the finishes that are actually colonized. Preservation and drying are compatible.