"Proper Handling" of Threaded PVC Joints

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by baumgrenze, Sep 20, 2010.

  1. baumgrenze

    baumgrenze Member

    Messages:
    32
    Location:
    California
    I decided this morning that I needed a refresher on just how much I should tighten threaded PVC joints. My first hit suggested that there was a whole lot more that I, and my trusted plumbing supply friends, had to learn.

    How many have read this FAQ on the Lasco website?

    http://www.lascofittings.com/

    Select the "Support Center" item in the menu on the left. One of the sub-items is "Installation." There appear to be several very interesting subjects. I will post an image of the entire menu tree b elow:

    As someone who has only been working with PVC on a DIY basis since 1997, I'm tempted to learn from the tech service department at Lasco. I figure they want us to have the best experience we can when we use their products. I'm interested in hearing what others on this forum think.

    Thanks,

    baumgrenze

    [​IMG]
  2. baumgrenze

    baumgrenze Member

    Messages:
    32
    Location:
    California
    For some reason, perhaps length, this part of my post refused to show in the Preview and in the post above. I had placed it in the middle of my original message just after the first question:



    Here is the section that got my attention. I called my parts supplier and got a little more than incredulity. They just said, we always recommend Teflon tape.

    " Don't use Teflon tape, Teflon paste or pipe dope. Do use a sealant.

    Teflon tape, Teflon paste and pipe dope is intended for metal pipe and fittings. Metal to metal fitting joints are more difficult to tighten than plastic; the surfaces tend to gall without the aid of such lubricants as Teflon or pipe dope. Plastic fittings do not need this lubrication.

    When Teflon tape is wrapped around plastic male threads it adds to the strain and tensile stress. The tendency of most installers is to incorrectly wrap several thickness of tape around the male threads, increasing stain and stress further.

    Teflon paste and pipe dope, just like Teflon tape, make threaded joints slippery. Their use on PVC fittings can be an invitation to over-torque.

    When working with threaded plastic fittings do use a proper sealant. The right sealant for threaded joints is non-hardening, compatible with plastic and doesn't add slipperiness.

    A non-hardening compound is forced by water pressure into potential points of leakage, thereby performing a true sealing function. Tapes and hardening pastes permit a leak path to develop when a joint is backed off, mechanically flexed, or expands with rising temperatures.

    A sealing compound must be compatible to plastics. Many brands of pipe sealant contain oils, solvents or carriers that can damage plastic. A proper sealant must be certified by the manufacturer to be harmless to the fitting material and to not contaminate fluid in the pipe.

    Finally, a sealing compound must not lubricate the joint to the point that over-tightening is encouraged. Several sealants on the market meet all these requirements."

    I found no recommendations. My voice mail to Lasco was returned and I was told to try two products, IPS AllSeal and Permatex® Soft Set Thread Sealant 61 Blue.

    I did a bit more searching and learned that both of these products are oil based. About ten years ago I stopped using an oil based Teflon containing pipe dope on plastic because I thought it was weakening the plastic. I looked for the can, but I've misplaced it so I can't say what it was. The parts that failed were black plastic reduction tees that I used to install Pepco QuadraBubblers. Perhaps they were not PVC but ABS. Perhaps I just overtightened the joints because they were over-lubricated and easy to over-tighten.

    There are more articles on threaded PVC. You can access them from the Lasco home page:
    Last edited: Sep 20, 2010
  3. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
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    Location:
    Cave Creek, Arizona
    Interesting article. Now I can completely disregard the whole thing. Traditionally, PVC manufacturers HAVE recommended tape, but not an excessive amount of it, on a thread. I also tighten the joint as far as possible, since I do NOT want a leak after the system is put together. Oil based compounds will soften PVC and result in thread failure. The only way "pressure can force the sealant into voids" is if you put the sealant into the female thread so it is pushed into the joint ahead of the pipe
  4. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    It is an interesting website, and I am relieved that they confirm what many of us have preached.....hand tight plus one or two turns max. I was surprised about the "no tape/no teflon paste". I understand about the issue of lubrication leading to over tightening. I am not familiar with those other sealants. And of course, Oatey, Rectorseal, and Hercules all recommend their teflon paste products for plastic fittings.
    I will be cruising over to the PPFA website later to see what they have to say.
  5. baumgrenze

    baumgrenze Member

    Messages:
    32
    Location:
    California
    Thank you HJ and Jimbo for your responses. Thanks, too, for pointing me to the PPFA website. I took the liberty of searching it using Google and found 3 hits, all of which said, in essence, Teflon tape in moderation is always good; if you want to use dope, make sure it is labeled as PVC compatible. This suggests that Lasco is not in agreement with PPFA.

    FWIW, here is a technique for searching websites on Google that sometimes finds things that an 'internal search' using the search box on the website do not turn up. The URL below is for the search I ran:

    http://www.google.com/search?source=ig&hl=en&rlz=&=&q=site%3Awww.ppfahome.org%2F+threaded+pvc+"teflon+tape"&btnG=Google+Search

    Here's the full text, unlinked, so you can see all of it:

    http://www.google.com/search?source=ig&hl=en&rlz=&=&q=site%3Awww.ppfahome.org%2F+threaded+pvc+"teflon+tape"&btnG=Google+Search

    The URL represents a Google search for the following search terms:

    site:www.ppfahome.org/ threaded pvc "teflon tape", where the site:www.ppfahome.org/ term asks that only the PPFA website be searched and the terms threaded pvc "teflon tape" ask that the terms threaded pvc and the term [/I] "teflon tape"[/I] be searched only when the two occur next to each other.

    I will email Lasco my results and ask for their comment. I will also ask about the long-term compatibility of oil-based pipe dopes with PVC fittings. Both of the products they recommended are oil-based. That make sense because they are intended to be "non-drying" or "non-hardening" and fluid enough to flow into the open spaces between the root and the chamfered crest of the two threads.

    For the sake of completeness, here are the three PPFA web pages that Google found:

    http://www.ppfahome.org/cpvc/faqcpvc.html

    http://www.ppfahome.org/fittings/faq-fittings.html

    http://www.ppfahome.org/Attach/PVC_Design_Guide_Approved.pdf

    Of the three, the second one taught me the most. It is full of received wisdom regarding cemented PVC joints, too. I now know that I should always chamfer the cut edge of a piece of pipe before applying primer and cement because a sharp edge is more likely to scrape some of the cement inside the female fitting to the inside end of the fitting instead of leaving it in the joint. The recommendation that female PVC and male metal joints should be avoided and that female metal and male PVC be used instead was also new to me. It makes sense because a metal male fitting is more likely to split a female PVC on than vice-versa.

    Enough! It is time to join some pipe.

    baumgrenze
    Last edited: Sep 21, 2010
  6. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,835
    Location:
    Cave Creek, Arizona
    A "formula", such as "hand tight and two additional turns", ONLY works when EVERY thread is formed to a perfect standard, and your hand tight is the same as mine. I have NEVER found PVC threads to be that consistent.
  7. asktom

    asktom Member

    Messages:
    575
    Location:
    Victor, MT
    Why is it nobody makes a one piece Sch 40 transition fitting like they have for CPVC - brass/plastic? I have found Sch 80, special order and a price that chokes you up, but never Sch 40.
  8. baumgrenze

    baumgrenze Member

    Messages:
    32
    Location:
    California
    As I began assembling parts this morning, I was frustrated because the mold line on the short nipples I taped and inserted was clearly displaced, meaning that there were two sets of threads, offset enough so that it was obvious to the eye and hand. It is asking a lot that such a thread and the associated tape conform enough to make a water-tight seal. If you combine that with a similar poorly molded coupling, it is a wonder that joints hold. I'd lay it all on China's doorstep, but I'm remembering the Breckenridge T-111 paneling our contractor paid big $ for; it was regrooved to match the narrow batten paneling on our 1955 Eichler post-and-beam house. The underlying product, from Roseburg, OR, had been gang-saw grooved with a very dull equipment that should have been swapped out hours earlier. The inner plies of the plywood were so filled with large voids that it was a major task to fill and stabilize it for painting. It was hardly fit for use as the exterior of a temporary FEMA trailer, but it was represented as 'the best we can get.' How do we get vendors and manufacturers to reinstate some semblance of quality control?

    Sorry for the rant, but it was frustrating to look at the poor quality fittings I had in hand and to know that no amount of shopping would find me better quality ones.

    baumgrenze
  9. baumgrenze

    baumgrenze Member

    Messages:
    32
    Location:
    California
    Just for the sake of completeness, I was doing an inventory of fittings and found the missing pipe dope in the same drawer with them.

    http://www.laco.com/prod/118/slic-tite-paste-with-ptfe.aspx

    Here's how they describe it:

    Key Benefits:

    * Contains more PTFE than other national brands.
    * Non-toxic, non-drying, washes off easily.
    * Sealing temperature: -50°F to 500°F (-46°C to 260°C).
    * Pressures: 3,000 PSI (204 BAR) for gas, 10,000 PSI (680 BAR) for liquid.
    * FGG/BM/CZ® System Compatible.


    Key Applications:

    * Use on metal, PVC, CPVC, and ABS plastic pipe threads.
    * For sealing water, air, steam, natural gas, LP gas, refrigerants, ammonia, gasoline and oil. See Application chart for other service uses.
    * USDA approved for use in federally inspected meat and poultry plants.

    Note that they recommend it for PVC, CPVC, and ABS threads. Some pipe dope manufacturers exclude ABS.

    Perhaps my joints failed because I over-tightened them and the product was not at fault. I'm not tempted to experiment further.

    baumgrenze
  10. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,835
    Location:
    Cave Creek, Arizona
    I have NEVER had a PVC joint fail because it was "overtightened", but have repaired many that became loose over time.
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