Replaced Portion of Cast Iron Plumbing Stack with PVC and water if now forming on the outside of the new PVC pipe

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NicoleChristine

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We need your help.

We replaced a portion of the cast iron pluming stack with PVC. We are now noticing that water is forming on the outside of the PVC pipe just below the section where the cast iron and PVC join.

I have attached pictures to show you where the water is forming (shaded / circled in blue) as this seems to be the wettest area. We think from this section it flows down the pipe.

The water is forming on the backside of the pipe, which is on an exterior wall. The house was built in 1880's. Walls are double brick with no insulation.

I'm located in Ontario and it's -8 °C or 17.6°F outside.

The existing cast iron above the new PVC (that vents out of the roof) is dry. The front of the pipe (facing into the room) is dry.

There is no water in the pipes. It has not rained or snowed recently. When we connected the PVC to the cast iron, we ran water into the pipes and there were no leaks. This was a few days ago.

When we put our hand behind the stack (where water is collects) we do feel a cool breeze coming in. When we dry the pipe the water forms again within 5 minutes.

We think it could be condensation, but it doesn't really make sense to me that an empty PVC pipe against a cool wall could form that much condensation.

We could really use your help as we are not sure what is causing this and what we can do to prevent it from happening.

Thank you,
Nicole

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Badger47

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I am not a plumber..these are just comments
The Fernco is not designed to support weight--the cast iron pipe above must be totally self-supported.
Your Fernco(s) looks to be in bad shape--squished.
The air rising through the pipe is hot (compared to the pipe) and very moist.
This moisture is condensing and running down the inside of the pipe--normally you wouldn't notice it because it runs into the sewer.
The squished Fernco will allow some of this water to leak into the house(it could also be a faulty glue job on the pipes).
The Fernco coupling need to be tension free and really tight!
 

Breplum

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They make special transition fittings for plastic to cast iron because the o.d. are different in pipes over 2" size.
Your piping is called ABS not PVC but that is irrelevant in this case. Just make sure your glue/cement is ABS not PVC cement !!
Banded couplings all must be tightened to specific torque. A "T-torquer" tool is necessary for that.
 
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