Troubleshooting water damage on plaster wall in old brick home

[justajane]

On one of our dining room walls we have a perfect storm of variables, and not surprisingly we have extensive water damage on that wall. When we moved in, there was a 4 inch up/down plaster crack on the wall with crumbling powdery plaster coming out of it. Since it didn't appear to be getting worse and we were newbie homeowners, we just put a chair in front of it and called it a day.

Fast forward six years and I decide it is time to fix it. I watch countless plaster repair videos and decided to tackle it myself. This also corresponded to when we were painting the dining room. When  I was cleaning out the damaged plaster, I realized that the original cast iron stack was running right behind the crack. Eureka! But since this is a very costly fix that basically means gutting the floor of the original bathroom upstairs, we've decided to make that a four year project if we can make it that long.

I was pretty pleased with the plaster repair results, but not surprisingly within three or so months, the new plaster was already getting moist again and producing this kind of efflorescence on the surface of the paint. In addition, there are multiple other places now where the paint is bubbling under the window sill and up further on the wall away from the stack and the window.

Needless to say, we are flummoxed. I'm guessing that the original damage is from the cast iron stack that is slowly releasing water, but it didn't feel wet to the touch when I uncovered it. But what is causing the other damage on the wall? Is it faulty mortar joints?

Here's the perfect storm of variables on that wall:

Original plumbing running through the plaster on brick.
chimney on that side (but up two stories)
directly above the return vent for the whole house
air conditioning directly outside with a furnace exhaust and a pipe that pumps out cold water

I wanted to solicit experiences from those of you who have dealt with this type of water damage. In your experience, what are the likely culprits? And with damage this extensive and random, do you think we need to have the entire wall re-tuckpointed? Can water travel that far down from the chimney? There's no damage above it on the second floor.

Any feedback or guidance would be much appreciated.

[monarda]

My guess is you just needed a new wax ring on the toilet upstairs. Years ago.
If you've let it go for six years, the upstairs bathroom subfloor might be  (likely) rotted, so a simple wax ring won't work, you'll need to check and perhaps repair the subfloor.  Get a proper diagnosis from a plumber.
You shouldn't put off this repair if that's the problem. The subfloor will only get worse and the ultimate repair will get more expensive.

(Ask me how I know this)

[Indio]

Water can travel in the most unusual ways along the bones of a house. I would start with the bathroom first to detemrine if that is the source. I have palster walls throughout my house and got so tired of fixing all of the cracks that I finally sheetrocked the kitchen ceiling because new cracks kept coming out daily. Wallpaper is another way to hide a plaster wall that doesn't want to cooperate, but first you need to find that source of water.

[Greg]

Sounds like you have an active water leak.  Could be the plumbing vent roof penetration, could be the chimney flashing, could be the cast iron drain.  It will be difficult to diagnose unless you expose the pipe or other area to visually see the leak.  That's what I would do, otherwise you'll be guessing. 

I'd open the wall back up to expose the cast iron pipe all the ceiling and beyond if possible, and leave it open to watch for leaks.  I'm talking days, weeks.  If it's hard to see wetness, use talc to dust the surface and watch for the talc to become damp.  Lights are a good idea.

As has been mentioned by others, water can travel along framing and plumbing in surprising ways, but usually flows downhill.

[justajane]

Thanks for your suggestions everyone. I never thought about the wax ring, thanks! Our four year plan is to gut that bathroom entirely, floor included. It slopes terribly and will need to be leveled. I wonder if we could wait that long? I am loathe to spend any more money on that bathroom, since it will all be replaced.

So, tuckpointing is the last guess? I was thinking of calling a tuckpointing company to give their two cents. We have had two separate people tell us the chimney needs to be re-pointed. I just couldn't fathom how that would cause damage exclusively so far below and not elsewhere on the wall.

Thanks again!