Green Board Fails Again To the Editor: In your On the House section in the January 1995 issue, you responded to a question about vapor barriers and potential moisture problems. As the past customer service manager for a major builder, I had the unfortunate task of rebuilding approximately 30 ceramic tile shower enclosures due to problems created by the presence of a vapor barrier. The problems occurred because the exterior walls of the showers had a 6-mil polyethylene vapor barrier over the inside face of the insulation. Green board drywall was used over this, and then ceramic tile applied with mastic. Because of the cold winter weather outside and the high moisture/humidity inside the shower, the vapor barrier provided an