Crumbling material behind the caulk seam in the tub?
I own a condo I bought a year ago. The condo building was built in the 1940s and the tub is the original. Today, I removed some caulk in my tub in order to re-caulk it. There is some crumbling material (brown dirt-sized particles) that is behind the caulk in the seam. I vacuumed it up and the particles are gone now.
Is that a sign of water damage done to the walls behind the shower?
Should I just re-caulk it and forget it? Or is it a sign of mold?