I am a faithful reader of your Sunday articles and find them both useful and enjoyable.
Now I need your expertise
We live in a 56 year old two storey home with two bathrooms. The upper floor is not being used any longer, due to my wife’s inability to get upstairs. Several years ago the upper bathroom toilet started staining the ceiling below in our kitchen. It was not a serious leak, so I pulled the toilet and carefully installed a new wax ring. Unfortunately, that did not solve the problem.
However, it finally stopped leaking for about 2 years, so we assumed everything was okay. That was a bad assumption and we installed new ceiling tiles over the old plaster. Now, it has started to drip again and we are not happy campers. An old retired plumber friend said that our lead soil pipe attached to the stack is the problem. He said that he replaced many of these as they get paper thin and leak.
To get at this pipe would be a nightmare as the kitchen cabinets cover the area of the stack and access from the hallway behind would be even worse. The plaster ceiling in that area curves to cover the upper staircase.
Do you know of any method of re-lining this pipe, perhaps with something like thick body shop type epoxy? I am clutching at straws for some good news.
Unfortunately, when we make assumptions based on minimal knowledge, we may live up to the old cliché. Currently, you are still making an assumption that may be just as big a mistake as thinking that the leak would stop on its own. You are under the impression that the leak is caused by an old, deteriorated lead drain pipe. Without opening up the ceiling in the area below the bathroom, there is no way to confirm that suspicion. I will offer more than one possibility for the leakage, but unfortunately there is no magic bullet for the repair.
The leak may indeed be due to a worn out lead toilet drain below the upper bathroom. This may be due to simple age, loss of a seal at the main stack, or mechanical damage to the drain from nearby joists or other objects. It is a common occurrence for a slow leak to develop from this type of deterioration, but it will not often stop happening for a long period of time, as in your case. The slow leakage is common because the water in the toilet drains is under minimal pressure, except when the toilet is flushed. With low pressure, a small leak may only drip minimally, or only when the toilet is emptied.
The difficult part of your blind evaluation is that this type of leak is also similar to that from an old galvanized supply pipe. Galvanized supply piping will rust over many years and do so from the inside out. As the inside of the pipe corrodes, the diameter gets smaller and the water pressure decreases considerably. Once this becomes quite advanced these supply pipes may leak very slowly, stop for a period of time as the rusty leak crusts over, then finally leak slowly but more consistently. This process may continue for several years before the leak becomes large enough to cause major moisture damage. As you are only flushing the toilet occasionally, this is as likely a cause of the leak as a damaged drain. If you have previously upgraded the supply piping to copper or plastic then this potential culprit can be dismissed.
Finally, the leak may also be due to a small, hairline crack in the tank, worn seal between the tank and bowl, or loose fittings for the supply piping. This would be more visible from the bathroom side of things, but may be somewhat hidden behind the toilet. Furthermore, the location of the moisture stains in the ceiling is not always an indication of the location of the leaking plumbing above. Water will drain to the low point in the ceiling and might only drip through a light fixture or small hole or crack in the ceiling at a remote location from the actual point of entry. The source of the leak could easily be due to damage in the sink or bathtub plumbing, as well.
As I often say to my kids, “there are only two ways to do something; the right way and every other way”. In this case the right way is to remove the stained section of ceiling plaster, as it is already damaged, and continue until the source of the leakage is positively identified. This will also allow for a more thorough inspection of the floor sheathing and joists in the area to ensure that they are not rotten. Once the ceiling area is opened and the damaged pipes are exposed, your old retired friend can recommend an active, licensed plumber to replace the offending pipes and stop the leak.