why would joint compound or drywall mud turn gray and smell like sulfur. Is it safe to use? Lori?

Answer 1

Joint compoud is a chemical composition designed to change characteristics after being exposed to the air. (goes on wet and gooey, dries hard and sandable) Your container had air leaks, and some of the chemicals began to react and change form. Throw it away. One of the beauties of joint compound is that it is relatively inexpensive.

Answer 2

Sounds like it has mildew in it. My favorite to use is the lightweight kind.[the blue lid] You don't have to add water,It's a lot lighter in weight, and you don't have to stir the bucket first. Once you use that you'll never go back to the green lid again.