Repairing leak in PVC DWV joint

[Crashcup]

Hi, hoping someone here can offer some quick advice.

I'm air-testing a new PVC DWV system in our house addition (our county requires 5psi air for 15 min for the inspection). In 15 min the pressure goes from 5 psi down to about 4.2 psi, so I've got at least one leak.

I've found one leak so far, in the vent stack in the attic. The fittings are kind of close together in the area of the leaking fitting. When I cut out that fitting to replace, it will leave me with just a small section of straight pipe to fit a new san tee. But since I'm cutting it close, the part of the pipe the tee will fit on already had primer on it, and possibly some cement, on it from when I first assembled the fittings.

Will some cement on the pipe prevent me from getting a good joint with the new fitting? Will just having swabbed primer on the area be a problem?

I guess what I'm asking is what's the best way to prepare the pipe for the new fitting assuming it previously had primer, and possibly cement applied to it. I don't want to replace the leaking fitting only to find the replacement also leaks!

If I go back far enough from the leak to get clean, untouched pipe, that will mean replacing 4 fittings instead of 1... obviously would like to avoid this if at all practical.

Thanks much for any advice.
Keith

 

[hj]

Your problem may NOT be the cement and primer on the pipe, but rather not having enough pipe to bottom out in the hub. The other thing could be that they usually state on the pipe to NOT air pressure test it.

 

[Sponsor]

 

[Reach4]

I've found one leak so far, in the vent stack in the attic. The fittings are kind of close together in the area of the leaking fitting. When I cut out that fitting to replace, it will leave me with just a small section of straight pipe to fit a new san tee. But since I'm cutting it close, the part of the pipe the tee will fit on already had primer on it, and possibly some cement, on it from when I first assembled the fittings.

Will some cement on the pipe prevent me from getting a good joint with the new fitting? Will just having swabbed primer on the area be a problem?

Have you considered sealing the leak? Is the leak on the upper surface of a fitting, or the lower surface? Upper would be easier to seal. You can find videos of such repairs on the suction lines of pumps. You could put the system under vacuum with a vacuum cleaner to suck new glue, I would think. I have not done it.

Some plumbers can cut away a fitting without cutting the pipe away. It involves controlled saw cuts through the fitting, and then prying and chiseling. You can also consider using banded couplings.

I am pretty sure that primer applied previously will have no effect. It evaporates away, although the purple dye stays. I think it unlikely that a little cement would be a problem, but you should be able to detect that with a fingernail. You could sand that away or maybe use a single edge razor blade. It is the deeper part of the joint where the real seal develops.

I am not a plumber.

 

[Crashcup]

Thanks HJ, Reach.

County requires an air test, so not much choice there.

I am going to try sealing it by drawing in cement under vacuum. I know that's considered by many a temp fix, but this is my own house, and frankly with this joint on the vent stack, high in the attic, it will never see water, and I don't see much of a problem if it did leak a bit of sewer gas, which seems unlikely with no pressure.

Seems like a bit of pvc "sawdust", filed off a scrap piece, might be good to mix in with the cement to provide it with a bit more body for sealing the leak.

 

[Dj2]

The proper way to check a new DWV system is to cap it, install a 10 ft high vent, insert a garden hose on the top of the vent, fill with water and wait to see any leaks.
No leaks the next day? have the building department inspector see it and sign it off.
Leaks? repair them quickly and retest later. Don't let the inspector see them...

 

[Gary Swart]

Might be wise for you to learn that PVC "cement" or "glue" is NOT cement or glue.

 

[Crashcup]

The vacuum technique worked! Cleaned the joint as good as I could with plain water and a toothbrush. Then swabbed with primer, then turned on vacuum (shop vac connected to a CO fitting in the basement), swabbed cement around the leaking part of the joint. Had my helper cut the vacuum then continued to swab a bit more cement on to make sure it wouldn't "starve" the joint if it was still pulling it in.

Afterwards pressurized to 5psi again, checked that joint with soap solution and NO bubbles.

Pressure dropped slightly from 5 psi to 4.9 psi over 15 minutes. Getting close! Not being a plumber, I don't know whether the county inspector would buy off on that, so I'll have to continue to check the rest of the joints for more leaks.

 

[Crashcup]

Might be wise for you to learn that PVC "cement" or "glue" is NOT cement or glue.

I have learned that it is a solvent, that sort of welds the pipes to the fittings. Not sure I see how this relates, though?

 

[Cacher_Chick]

One thing to look for is if you used foam-core PVC, air can and will leak through the foam core. Anywhere you have an open-ended pipe with a test ball or plug in it, soap down the end of the pipe and check it. The riser for the WC is often a prime suspect.