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Discuss Seeping threaded fittings... *stainless/brass plastic* in the Plumbing Forum area at

  1. Deuce

    Deuce New Member

    Hi all, just joined to try and get a definitive answer on this!

    When connecting threaded fittings, metal of plastic, what single application thread seal product works best?

    We have tried:
    • PTFE + silicone. Virtually always seals but will seep if agitated after cured.
    • PTFE with Fernox general purpose thread sealant, still sometimes seeps on larger threads 1" or over, and can also fail if agitated after cured.
    And also just silicone on some ABS/PVC threaded fitting, as advised by the manufacturer (PTFE can react apparently).

    We have to quite often adjust the layout of the kit we assemble and we need to be able to make and break threaded connections relatively quickly, cleanly and not waste time re-working seals as we currently do sometimes. We use threads up to 2" max.

    Cost of solution is really not an issue as it's having way more impact on time than we can afford as it is. We also need to be really confident our kit will not leak/seep at all.

    I have been looking at Loctite 5776 (LOCTITE 5776 - Thread Sealant - Loctite) and wondered if anyone here had used it, or similar, or could reccomend another product.

    I guess as it's so important we don't get leaks, products used reliably for gas might prove most appropriate?

    Many thanks in advance

  2. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    577 is great but won't work on anything plastic

    Sounds like you need loctite 55 or boss white and hemp
    • Like Like x 1
  3. Chalked

    Chalked Plumber GSR

    As Shaun says . Don't use 577 on plastic! It ONLY works with metal.
    • Like Like x 1
  4. Deuce

    Deuce New Member

    Thanks both of you.

    How reliable/foolproof is 577 generally? For example silicone smoothed into first few threads is normally extremely reliable, initially. But it's not reliable long term. So we need a high tech product that seals as reliably but also copes better with a little movement over time. Can't use a thread 'lock' product though as we do need to be able to break the connections sometimes..
  5. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    Never had a leak and you can disassemble when you need to
    • Like Like x 1
  6. Deuce

    Deuce New Member

    Have you used on threads up to 2"? And I assume just the 577, no other products used alongside it?
  7. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    Yep and straight medium non tapered pipe

    Even done an pita 4" one that was in a floor

    Follow the spec tho eg need to clean the cutting oil off before you apply it
    • Like Like x 1
  8. Last Plumber

    Last Plumber Plumber GSR Top Contributor!!

    I take it this is a threaded joint?
    What are you putting together?
  9. Deuce

    Deuce New Member

    That's very reassuring to hear! I'll get it ordered.

    Yes we clean the fittings, we use loctite spray cleaner.

    Thank you so much for the help ;)
  10. Best

    Best Trusted Plumber Top Contributor!!

    Don't use actual Boss White on anything plastic. It is oil based and will react with most plastics and destroy it
    • Like Like x 1
  11. Deuce

    Deuce New Member

    Yes, threaded fittings. Everything else we don in solvent weld as far as possible.

    The equipment itself is mostly pool filters/pumps. Which are normally all done with solvent weld. But we have to make the kit modular, mobile and very tough, so we often go onto stainless/brass fittings. We use composite bulkheads to go from one to the other unless we have no choice but to directly mate metal and plastic threads..
  12. Deuce

    Deuce New Member

    Thanks. As it happens I just ordered Loctite 5331 for the plastic threads. So should be all OK.
  13. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    Loctite 55 for metal to plastic threads
    Loctite 577 for metal to metal threads
    • Like Like x 1
  14. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    Never tried that myself let us know how you get on
    • Like Like x 1
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  15. Last Plumber

    Last Plumber Plumber GSR Top Contributor!!

    I see. I was asking just to make sure that they are taper threads and not face joints.
    If you've sorted it, then all's well and good.
    • Like Like x 1
  16. Deuce

    Deuce New Member

    Most are taper threads, some straight. For straight we normally apply sealant on male and female, rubbing it down right into the threads before assembly. This generally means the sealant isn't just pushed down the female thread. Obviously a lot is... But we don't have to worry about contamination as not potable water. Also anything that is pushed down the thread, will get picked up by filters down the line.

    But is there a better way for straight threads?
  17. Last Plumber

    Last Plumber Plumber GSR Top Contributor!!

    More often than not, yes.
    What make/ type of fitting are you using and I'll let you know if there is a better way.
  18. Deuce

    Deuce New Member

  19. Last Plumber

    Last Plumber Plumber GSR Top Contributor!!

    Most look like taper threads. The ones that aren't sometimes you can get a fibre washer to sit in the female if there is a shoulder inside so that the male will screw right down onto it but that is normally only possible when the male will screw fully in easily, as in parallel threaded or not tapered enough to tighten into the female thread, if that makes any sense at all?

    Do you use BES?
  20. Deuce

    Deuce New Member

    No shoulder in the female sockets usually. Yes even parallel threads often don't go all the way without quite some effort... plus the thread itself isn't often fully cut for the last 10mm of some fittings. With parallel we probably get less leaks though, as we simply got OTT with sealant. which is messy, yet effective.

    We do use BES and others. It really depends what we need and lead time to be honest.
  21. Last Plumber

    Last Plumber Plumber GSR Top Contributor!!

    I tend to use Loctite 55 on metal threads. Never tried it on plastic though.
    Last edited: Dec 6, 2017
  22. quality

    quality Plumber GSR

    Sorry to butt in here but Ive used 577 since it was introduced in the early 90`s is 5776 something new?
  23. Deuce

    Deuce New Member

    It's just a variant within the range, fast curing. Which for us is good.
  24. quality

    quality Plumber GSR

    I will stick with 577 it ok above 60 degrees but 5776 maybe cheaper
  25. Deuce

    Deuce New Member

    The only difference I can see is that 577 says it will lock the thread, whereas 5776 says only seal. Price is the same, £20 ish for 50ml (without discount).

    As for price, I would pay £300 a tube for something that was always 100% reliable. £500 if it was overseas work :eek:

    Our work goes into TV & film studios with 400v power cables strewn across the floor, £200k per day downtime costs etc.. threaded fitting are not the most popular subject in our workshop..
  26. quality

    quality Plumber GSR

    Hey ho everyday is for learning
    • Like Like x 1
  27. Chuck

    Chuck Active Member

    Try calling the Henkel/Loctite Technical hotline:

    Contact & Services - Loctite

    I've never called them myself, but they're a serious outfit so I'd expect them to know their stuff.
  28. Deuce

    Deuce New Member

    I did just before posting on here - they transferred me to the right department and all I got was a voice recording saying technical services were down due to a technical fault haha!!!

    But yes, given their prominence (and prices) I'm sure on a normal day their tech support is first rate.
  29. oz-plumber

    oz-plumber Plumber

    I can't fathom how you are having so many problems with threaded fittings.
    You are obviously having major problems, hence coming on here.

    Are you putting the tape on the correct way?
    Is the tape not gripping to the plastic fittings and spinning / slipping.
    Try roughing the threads up a little, so the PTFE grips to the thread.

    We did some waterlines recently that were between 1400kPa & 1600kPa, used PTFE tape on all the threaded fittings and didn't have one drip. The largest fittings were 50mm
  30. rpm

    rpm Trusted Plumber

    The equipment itself is mostly pool filters/pumps. Which are normally all done with solvent weld. But we have to make the kit modular, mobile and very tough[/QUOTE]

    Pool pumps & filters are quite low pressure things even on 2" so don`t see why you struggle.
    You tried these?
    Mega Union coupler | Bosta UK Ltd
    Come threaded for plastic or metal pipes or solvent weld
    • Informative Informative x 1
  31. Deuce

    Deuce New Member

    Yes we use hundreds of those a year. Fantastic as the seal is perfect each time and allows components to be switched out in moments, tool free. But sadly the pump/filter ports themselves are threaded, so threaded seal connections still exist in the system. We don't struggle so much with the pool kit really though. But when we have 3000 solenoids all with threads going into a single distribution manifold, all of which have to be (and remain) leak free, even a 99% success rate would mean 3 leaks per assembly. So that's why we're looking for quick and foolproof sealants to use.
  32. Deuce

    Deuce New Member

    Not major problems, it's just the sheer number of connections and importance of zero drips that makes me seek the ultimate product/method.

    But what you have said is quite concerning. PTFE is not generally good for plastic threads. It increases the internal pressure on the female fitting, which combined with a medium to long term reactions with certain plastics can cause the fitting to split. We have had that happen. As your lines were 14bar pressure any such additional pressure on the fitting could be critical.

    The thing is, I agree PTFE does work very well on plastic fittings. Initially. But it's a thread lubricant, sot sealant. Any future agitation and drips tend to start. And over time as the tape shifts and compresses the same can happen. But the worse thing is, the reason it works so well on plastic is it allows you overtighten the fittings - causing a fantastic seal initially but at the expense of over-stressing the female fitting.

    It does depend entirely on the type of plastic fitting of course. If it were a GF reinforced PP fitting, as many pressure fittings are, then no problem. That stuff's near indestructible. But ABS and especially PVC, teflon tape is really not correct.

    We genuinely have had quite a few 1.5-2" PVC threaded fittings split due to the use of PTFE. None were above 3bar pressure. And none split due to water pressure, it was the non-design force from the PTFE that did it. Most common when we combined PTFE with silicone as this made over-tightening very easy by even the most sensitive of hands. That was in the early days and not used PTFE of plastic since.
  33. oz-plumber

    oz-plumber Plumber

    How many wraps do you do with PTFE tape on each size of fitting?

    If someone asked me for a quick and fool proof method of sealing a threaded joint - I would reply PTFE tape.

    For pool equipment under minimal pressure, I wouldn't consider using anything else on any size of fitting
  34. oz-plumber

    oz-plumber Plumber

    My post may seem not to answer the question - we were posting at the same time.

    If you are having fitting split after a while due to stress on the fitting due to PTFE tape, I would find another type of fitting.
    I would put that down to the quality of the plastic in the fitting not the jointing method
    • Like Like x 1
  35. Deuce

    Deuce New Member

    It really depends on the exact scenario and fittings to hand. Generally 3-4. That doesn't remove the issue of extra pressure on the female fitting though as you don't know whether or not the tape shift/creases/folds as it's tightened. 4 wraps could in one spot be the equivalent of 7 wraps.

    You're outside of most manufacturers advice when it comes to the use of PTFE on plastic. Although, if you're not willing to consider anything else, I guess you have no option!

    The only manufacturer I have spoken to that does say teflon tape is ok is spears. But even they stipulate no more than two tooled turns of the threads beyond finger tight. Effectively leaving at least half the thread exposed in most cases. And in any case, they like others prefer the use of sealant in general.

    It also has little to do with line pressure. Yes swimming pool kit is relatively low pressure. But I have seen pvc fittings split due to PTFE use on drained systems sat in storage.