Patching PVC vent leak

[zver11]

I have a vent stack with a leak at a joint. Condensation keeps the joint wet. Location/obstructions makes it difficult to cut out section and replace joint but I can do a PVC repair coupling type patch. I can squeeze in a threaded clamp around the pipe to hold the repair in place until the glue dries. The problem is that the site is never dry.

I would rather not wait until spring for a hot day to do the patch. Is there any way to create a dry joint?
Pipe is 3" PVC just above a Tee feeding in 1.5" sink drain on top story of house. Attic above is very difficult to access given large amounts of blown in insulation and no flooring, joists not visible due to insulation.

I can access an area of pipe below the joint since I tore out damaged ceiling area. Would packing ice around pipe 2+ feet below joint work (force condensation lower in stack)? Would blowing in air from shop vac through sink drain pipe work?

 

[Cacher_Chick]

We cannot see what you can see, but my first thought is that a vent should not be THAT wet. My second thought would be to just cut out and remove the tee, pushing the stack up, and then cut in a new tee with new stubs of pipe and a pair of shielded couplings.

 

[Sponsor]

 

[Reach4]

Maybe I misunderstand. I am picturing a 3 inch vertical PVC pipe into the top of a tee. No signs of purple primer on the pipe, so you think water is coming out of the unglued vent line at the top of the tee. Not going to happen because your joint is not under pressure, and water flows downhill.

Tie a strip of cotton cloth above the suspect joint, and I expect it gets wet, because the water is not coming from the suspected joint.

 

[zver11]

I can see exactly where leak is. Area above leak is dry. Joints properly primed and glued with the exception of a makeshift transition which did not come down perfectly straight when forcing assembly between fixed top and bottom pipes. transition was slightly loose, but expected seal to work by bottom rim of pipe vs top rim of sched 40 insert fitting stop. Transition did not push down all the way. Because gap was against back wall with drywall on it, I did not see it at time(1/8" gap at worst point).

Stack is venting multiple bathrooms. Inside is warm outside currently cold. Surprising amount of condensation. More moisture coming down stack when its raining. With back of wall opened up around fitting moisture mostly evaporates before drip except during rain. But local area of leak too wet to glue.

Cut and replace would be first choice but difficult here. 3" PVC pipes fitting fit in 2x4 wall(3.5"deep) and divert around medicine cabinet involves multiple fittings close together transitioning between schedule 40(4"OD at fittings) and schedule 30 pipe and turning 45 degrees. Would need to cut pipe downstairs in ceiling to give enough movement to insert a fitting. 2x4 bracing cage around medicine cabinet further limits movement.

 

[Reach4]

Look at Leak-B-Gone 3 in. PVC Repair Ring. I have never even seen it, but it may match what you need.

Another possibility is to wrap the leaky area with self-fusing silicone tape, and then cover that with a strong stretchy tape to compress the silicone. That outer tape might be Scotch 35 white electrical tape, to be less conspicuous on PVC pipe.

Just to be clear, I think you have one of these, but inverted from the picture probably:

I think you are saying that the leak is at the top (as installed) part and not the side or bottom, right? Weird.

 

[zver11]

Look at Leak-B-Gone 3 in. PVC Repair Ring. I have never even seen it, but it may match what you need.

Another possibility is to wrap the leaky area with self-fusing silicone tape, and then cover that with a strong stretchy tape to compress the silicone. That outer tape might be Scotch 35 white electrical tape, to be less conspicuous on PVC pipe.

Just to be clear, I think you have one of these, but inverted from the picture probably:

I think you are saying that the leak is at the top (as installed) part and not the side or bottom, right? Weird.

 

[zver11]

Leak is not actually that joint. There is a stub of sched 40 3" pipe in the top followed by an insert coupling (Female/Female slip) connecting the Tee to the sched 30(thinwall) PVC pipe. The coupling extends into the upstream pipe on the inside. The flow is down the side of the upper pipe and between the pipe wall and the insert coupling. Insert adapters were used as opposed to conventional external couplings to limit the thickness to fit in the wall as a conventional 4" OD coupling would bow out a 3.5" standard 2x4 wall cavity. I will look into the silicone tape. I can make a repair ring. The problem with any form of PVC repair ring is that the joint must be dry before priming and gluing. If the silicone tape will work on a surface that is briefly dried off, it should do the trick.

 

[Reach4]

Leak is not actually that joint. There is a stub of sched 40 3" pipe in the top followed by an insert coupling (Female/Female slip) connecting the Tee to the sched 30(thinwall) PVC pipe. The coupling extends into the upstream pipe on the inside. The flow is down the side of the upper pipe and between the pipe wall and the insert coupling. Insert adapters were used as opposed to conventional external couplings to limit the thickness to fit in the wall as a conventional 4" OD coupling would bow out a 3.5" standard 2x4 wall cavity. I will look into the silicone tape. I can make a repair ring. The problem with any form of PVC repair ring is that the joint must be dry before priming and gluing. If the silicone tape will work on a surface that is briefly dried off, it should do the trick.

Silicone tape fuses to itself. It does not adhere to other things well. But compress that with other tape, and I think it should do the job. I have used it.