Mildew on interior outside walls, no water in attic, house built 1910, plaster walls. What causes this and how to fix, also paint and plaster coming apart in bathroom.

 

Sounds like you have an excessive moisture problem in your bathroom.
Ventilation is the solution.
You need to install a bathroom exhaust fan, or replace the one that you have with a more powerful fan motor.
Good luck!

 

Why then would it be mildewing in the rest of the house? I mean, the bedrooms outter walls get this way if anything is near the wall. With only 700 sq. feet of living space, some stuff needs to be at the wall.

 

Again, it is a matter of excessive moisture in the air and poor ventilation.
A properly working airconditioning system should dehumidify the entire home, or look into installing free-standing dehumdifier(s).
Good Luck!

 

I had the same problem in my 54 y/o house. In the bath room I installed a short blade small ceiling fan (the smallest they had). It doesn't interfere with the bathroom and I keep it on low all the time (pulling air up and pushing it toward the ceiling). That way the air circulates behind the shower curtain. I also have a dehumidifier in the adjacent room. This has helped considerably. It didn't completely resolve the problem though. I guess the next step is to install an exaust fan (lot more work). Just thought I would share my experience. I am by no means an expert. take care.

 

Well, I had a contractor come in and say that he's never seen it before. He seems to think it's a lack of insulation in the walls.