I have a 100 year old three family townhouse. The cast iron waste
stack runs up through a wall between the closet on each floor and the
airshaft. Also running in this wall are the vents for the bathrooms
and kitchens of each floor.
During renovation of the the top floor kitchen, a section of this
wall was opened up to gain access to plumbing and to run new electric
up from the basement.
Now that a section of that wall is open I can occassionally smell
I do not smell it in our bathroom (of course there is a bathroom and
kitchen on each floor where the tenants live and I have not journey
into their apts). I smell it in only in the wall.
Any suggestions on how to determine where the smell is coming from?
How can I figure if it's coming from a hole/crack in the waste stack,
or the vents?
Thanks for your help!
Maybe someone has a better idea, but chances are you are going to need
to start opening the wall up until you find it. With luck you will find it
at a joint and can re-seal the joint. At 100 years you are getting towards
the end of the lifetime of that pipe. It may have another 100 left in it or
it may need total replacement. I suggest if you do need to replace it that
you replace it with the same cast iron that is there. Good for the rest of
your life anyway and it will be quiet. Using a plastic replacement (or
really bad a plastic patch, as other parts will just fail soon) will result
in noise you will not like.
No real easy answers to this one.
I would not automatically assume that the source of the leak
is the stack.
Remember that all of the waste water from top down flows inside the
stack. A hole/crack or joint problem will *usually* leave some
tell-tale sign of water leakage. Look in the wall with a bright
light to check.
More common is a toilet bowl not tightly sealed to the Closet bend.
A failed wax ring can allow ater to pass thru without leaking but still
allow sewer gas to escape.
I have used a gas-leak detector instrument (normally used for
natural gas piping) to find sewer gas leaks. May not be practical
where the wall isn't open completely.
You can inject wintergreen oil into the stack to generate an
easily traceable odor or use a commercial smoke generator to
visually locate small leaks. These tests begin to get beyond
what a homeowner can do.
My gut instinct is that it is in one of the old lead vents that connect to
There is no gas smell near the toilet. At least not the toilet on this
yes indeedy, blowing smoke is what some of the plumbers I've met have done
The wintergreen oil idea is interesting. When you say "inject" it, do you
mean pour some down the stack from up on the roof? How much would you use?
a pint? a gallon?
This problem is 99% solved.
I went up onto the roof and looked down the waste stack with a flash light.
Completely blocked at the elbow just below where it goes through the roof!
Used a piece of metal conduit to poke at the blockage, loosening it up and
sucking it up with the shop vac - I didn't want to let lots of it go down,
some did of course, but a lot got sucked up. It was a very fine, dark
black, granular substance. What was that? Get shivers just thinking what
it might be. Bleck.
Once I cleared the blockage I could smell sewer gas rising up through the
top of the waste stack. Hallelujah! Finally coming out where it is
supposed to! And inside the house, so far, I would say the smell has
decreased by 99%. In the past 48 hours I only smelled it once eminating
from the opened section of wall in the kitchen, and it was slight compared
to the gagging amount that was there before.
What did I learn? Before complicated and expensive smoke tests and ripping
out walls I will always check for blockage up at the top of the stack. :)
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