need a sealant for pipe threads that WORKS


Old 08-20-13, 04:22 PM
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need a sealant for pipe threads that WORKS

I've just put in new plumbing lines that include male plastic threaded pipe going into galvanized unions and also into brass. I used a blue, gunky thread sealant called "Megaloc" that did NOT seal the threads. It failed right away when the water was turned on, especially where plastic male threaded pieces went into the galvanized unions.

Could someone please suggest what will really seal these threads? I'm so bummed out because it leaked right away after all the work. Someone at local hardware store recommended TFE Paste, but before I try another thread sealant I thought I'd ask here for advice.

Should I use Teflon tape, or Teflon and the TFE Paste, or something else? What do you recommend?

Also, any suggestions for cleaning the threads so that the new sealant or tape will work better? These pipes are in place now and it's not easy to clean them thoroughly. I've used a toothbrush and paper towels but I can still see some of the blue gunk in the threads.

This is not a high water pressure situation. I had to replace the water pressure tank on a 20-40 well system with a submersed pump. Ended up using new piping -- plastic piping for the most part, with the old brass 'T' at the pressure tank and pressure switch, and 2 new galvanized unions so that I could detach the new pressure tank from the 'T' in case of failure, and detach the 'T' from the new piping in case of problems.

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Old 08-20-13, 04:25 PM
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Never, never paste on plastic fittings.... Only teflon tape. A couple turns only...

Use new fittings.. dont even bother trying to clean off the gunk...
Old 08-20-13, 04:28 PM
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I will only put plastic male fittings into metal female. Never the other way around as a plastic female with a metal male eventually causes the plastic female fitting to split.

I have never used pipe dope on plastic fittings. You can use some Teflon tape to help lubricate the fittings but basically just tighten the snot out of the plastic fitting. Pipe threads seal by intimately squeezing the threads together so tape & dopes are more lubricants than sealants.
Old 08-21-13, 02:08 AM
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I'm going to buck the trend. I have assembled a lot of threaded plastic pipe and fittings and the ONLY sealant I found to work consistently was a Teflon paste. You MUST, however, make certain that the label on the paste specifies it can be used with plastic pipe. My experience using Teflon tape was abysmal.

Rather than using galvanized unions I would suggest using plastic unions. They seal with an internal O-ring against flat faces. Use more unions and fewer threaded joints. Used solvent-welded (glued) joints wherever possible.

As for using male metal pipe/fittings in female plastic fittings...they make the female fittings with a steel band on the outside to help prevent the male fitting from expanding the female to the point of breaking. You won't find the banded fittings in the homecenter but will have to buy them from a plumbing distributor or over the Internet.
Old 08-21-13, 04:00 AM
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I agree on using Teflon tape only.
A problem I have found is that the threads on new metal fittings have snags and imperfections that can damage plastic threads.
I work with a fair amount of plastic and what has pretty much eliminated problems for me when joining plastic to metal is to fully tighten a metal nipple or coupling onto/into the part that will receive the plastic.

Another way to eliminate problems is to always use a plastic intermediary connector on anything you don't want to replace because of a damaged fitting (plastic pumps, valves, etc.) and don't over-tighten.
Old 08-22-13, 02:33 AM
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Thank you for these suggestions. I've got to ponder this.

I wish there was a way to test a join before the water goes on. By then it's really difficult to fix. If I hadn't built in unions it would have been a lot worse though.

I will look at plastic unions too -- didn't know they made them. The brass T has threads inside and out, so I can use a male plastic between the T and the unions. I agree about not using a female threaded plastic over a metal threaded male. I've seen the plastic piece crack in an installation that a local plumber did, not long after the work was done.

Thanks again! You've really helped me with this.
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