Can someone tell us what is the deteriorating paper that is on the back of the cement wall? Picture taken from inside after removing drywall/plaster lath of 1924 house in Southern California which had ongoing water leak/damage. Concrete on the outside but no one seemed to know what the paper is. Will be adding fiberglass insulation and drywall but concerned about trapping moisture and creating mold problem, are we asking for trouble? Do we need to demo existing exterior concrete walls to create weather/water barrier? Thank you.