First there has been been a crack running through a grout line which I put down to the floor flexing too much. I was going under the house to check and measure to put some more joist in to reduce the flex and noticed this strange residue on the underside of the compressed cement sheeting.
Any thoughts on this? Is the waterproofing compromised or possibly some moisture from the underside reacting with the sheeting? There is an overflow of the storm water which has had a workout lately possibly intruding some moisture?