To disinfect the walls, use a bleach and water solution.

It's important to find the source.

Be sure the attic is well ventilated. Install bath exhaust fans and kitchen exhaust fans to remove warm moist air from showers and cooking.

Inspect a small portion of wall cavity to make sure the moisture isn't penetrating from the outside. If it is, then make changes to prevent it.

I found this while inspecting a damp wall surface prior to repainting a dining room.

Michael

Thanks for your response, Brushworks. I will give you some details in case anyone has any more ideas. The situation is a little complicated. My wife and I are grabbing a (rare) rental house and finally getting out of the crummy apartment that we rented since November. I am in New Orleans and we still have not been able to get ourselves together on what to do with our house that had 7' of water for 2-3 weeks (Gentilly). There was an elderly woman there going into assisted living the family is known to us and they want to temporarily rent the house. The custodians of the property are out of town for a couple of weeks do I am driving the cleanup and minor rehab of the house so we can get in there. They whole interior is going to be repainted. They are very concerned that the plaster does not get damaged.

The mold was only behind furniture that was close to the walls (two rooms and a total of two to three walls) so I don't think it is a leak problem. That points to air infiltration coming in from the outside. The walls are stucco on the outside. I am guessing this place was built in the 40's; it is a raised house of about 1200 sq ft.

The attic ventilation seems to be an hodgepodge that is, unfortunately, typical. There is a power vent, at least one other vent near the peak of the roof and peripheral vents in the soffets that were covered, but the covers are coming off. I don't know, but I doubt that there is any insulation in the walls. AC is window units. I suspect that moist air is being drawn in between the walls by the power vent and hitting the cold plaster. The Furniture kept it from drying out.

I understand the the woman did a lot of cooking. The kitchen has an external vent, but it looks pretty clogged. Her health has not been too good lately, but I don't know if that cut into the cooking. I doubt that we can add a bath vent. If it were my house I would have one, but around here they are are of marginal use anyway since the make-up air is usually not going to be significantly better. Since the old ladies don't like it too cool, I suspect that the AC was not running much so it got humid inside. On the other hand, it does not take much of a temp decrease to make water condense in the Gulf South so the walls might could easily become damp.

I will be taking my console dehumidifier over. This time of year, I typically run it at night when the AC units are cycling on and off a lot.