Best sealant for threaded connections?

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scattershot

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I have a 3/4" PVC pipe that ends in a slip-to-threaded adapter that I'm screwing into a brass sprinkler valve with female threaded ports on the bottom.

Generally with threaded connections I use "T Plus 2" brand pipe thread sealant paste (PTFE). After I applied it, tightened the connections and opened up the water supply, I see a single drop of water coming out of the threaded connection on the supply side of the valve about once every three seconds. The pipe was fully tightened down without what I'd say is over-torquing. The drip is definitely coming out of the threaded connection at the valve, not the slip joint between the PVC pipe and adapter.

So, is there a doping material that you think would work better?

I've never had really good luck with teflon tape, but if you want to say it's really the way to go, how many layers do you wrap? When I used to try using tape I was never able to get that right.
 

scattershot

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This is going to sound like a dumb question, but when you say "try using Teflon tape first then pipe joint compound," do you mean to apply the joint compound over the tape? Or were you meaning to try them separately?
 

Geofd

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This is going to sound like a dumb question, but when you say "try using Teflon tape first then pipe joint compound," do you mean to apply the joint compound over the tape? Or were you meaning to try them separately?
no dumb questions first use the tape apply it clock wise then apply the paste over the tape then thread it in
 

scattershot

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Thanks. Two questions:

-- Overall how many layers of tape do you end up with, after some overlapping?

-- Any particular brand or type of pipe joint compound you like?
 

PlumbGate

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no dumb questions first use the tape apply it clock wise then apply the paste over the tape then thread it in
I usually apply it counter-clockwise. When applying clockwise it tends to bunch up on me and make a mess.
 

frodo

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When assembling threaded PVC fittings, a sealing compound that is non-hardening is the best. Recommended good practice is to use a thread sealant (not a thread lubricant) to assemble the joint to finger tight plus one and one-half (1½) turns, two turns at the most. Teflon tapes and hardening pastes can permit a leak path to develop when a joint is backed off, mechanically flexed or expanded with changing temperatures. Conversely, a non-hardening compound is forced by the internal fluid pressure into potential points of leakage; performing a true sealing role. The sealing compound must be compatible to all materials and media to which the joint will be exposed. Many brands of pipe sealants contain oils, solvents or carriers that can damage PVC. A proper sealant must be approved by the manufacturer to be harmless to the joint materials and not contaminate the fluid in the piping system. Finally, a sealing compound must not lubricate the joint to the point that over-tightening is encouraged.

recto seal
 

frodo

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little story that taught me a trick way back in the day
I was working on a 3'' threaded fire main. This was where the pipe came into the building
We cut and threaded all the pipes then turned on the system. NO LEAKS
then we pumped it up to test pressure. A single drip showed up where the tie in was
DAMNIT !!!!
unscrewed every thing. re doped and Teflon tape
the retest. MF little drip again. I mean 1 freaking drip every 3 minutes
we took it apart and reinstalled
re tested
SAME DAMN THING
Boss showed up to check on us, we told him what was going on..He went to his truck and came back with some lead wool and a small chisel. We packed the threads and tapped the wool in
turned on the water bumped it to test pressure and that damn drip was gone
 

scattershot

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no dumb questions first use the tape apply it clock wise then apply the paste over the tape then thread it in
This ended up working out well. Before I saw frodo's post on sealant types, I picked up some tape and Rector Seal Tru-Blu sealant at the local big box. Four tight wraps of tape plus the Tru-Blue resulted in a really good seal -- the Tru-Blu seemed to have a much better consistency for this than the T Plus 2 paste I'd been using. So to be on the safe side I let it cure 24 hours, and now with water pressure on it seems like a solid seal. The Tru-Blu can says it's vibration-resistant, so hopefully that means it won't be developing cracks. Thanks again for the advice on this.
 
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