FHB Logo Facebook LinkedIn Email Pinterest Twitter X Instagram Tiktok YouTube Plus Icon Close Icon Navigation Search Icon Navigation Search Icon Arrow Down Icon Video Guide Icon Article Guide Icon Modal Close Icon Guide Search Icon Skip to content
Subscribe
Log In
  • How-To
  • Design
  • Tools & Materials
  • Restoration
  • Videos
  • Blogs
  • Forum
  • Magazine
  • Members
  • FHB House
  • Podcast
Log In

Discussion Forum

Discussion Forum

Leaking Unions

Porsche998 | Posted in Construction Techniques on December 27, 2005 08:39am

I have completed plumbing the hot and cold water systems for my house under construction using copper piping.  I have been pleased with the results with one exception.  It seems that every union that I put in leaks slightly.  I have tried to tighten them without ruining the sealing face.  It seems that they all drip about a drop every 10 to 30 seconds.  Not much but they still all leak.  They range from 1″ to 3/4″.  In some cases the leak will disappear after awhile, but when the water is turned back on, the leak will show up again.  I know that the unions are sensitive to alignment but they all fit well.  Is a compound typically placed on the union face?  That is the only thing that I can think of.  Any thoughts are appreciated. 

Reply
  • X
  • facebook
  • linkedin
  • pinterest
  • email
  • add to favorites Log in or Sign up to save your favorite articles

Replies

  1. mike4244 | Dec 27, 2005 08:46pm | #1

    I am not a plumber, I have done a lot plumbing though. Unions should not need anything on the face or the threads. The only time I had a union leak was from a bad union. The face apparently was not flat. If all your unions that leak come from the same supplier, try another brand.I do not use dope or teflon tape on the threads of unions, is it possible that the tape ,if you are using it is folding over on  the face?

    mike

    1. junkhound | Dec 27, 2005 09:04pm | #2

      One nice thing about copper unions is that I've never had one leak, surprised to hear any do. 

      The comment about having gotten tape or some such onto the mating surfaces is one possibility.

      Also: re -  I have tried to tighten them without ruining the sealing face, you DO need to tighten them enough so that the face deforms slightly, typically about 70 ft-# (50N-m) on a 3/4 copper union is what I use,  a limp 5 ft-# = leak. 

      1. Porsche998 | Dec 27, 2005 09:24pm | #4

        Will check the mating surfaces and try again

    2. Porsche998 | Dec 27, 2005 09:24pm | #3

      Thanks - Will check

  2. wookie | Dec 27, 2005 10:15pm | #5

    I use Laco slictite ( paste teflon ) on water unions. A very small amount, just a light coat. It just helps lubricate and seal I think its just the quality of fittings, I just automaticlly do it on all unions anymore no leaks. Also works great on under sink drain slip nut fittings a light coat around tube drain slide bevel washer down and tighten nut works 99.99% of time on problem connection.

    1. Porsche998 | Dec 27, 2005 10:53pm | #6

      This wasthe approach that I was planning on taking - I think that there is enough variation in the seating surface to allow some weepage.

      1. wookie | Dec 28, 2005 10:00am | #12

        Slic tite will work with variations on seating surfaces not defects such as a burr as mentioned. Just torque it properly the lubed surfaces will mate up no problem.

  3. Shacko | Dec 28, 2005 12:18am | #7

    The problem with unions is that they are not made that good anymore.Most come from overseas. What I do is put a little pipe dope on the threads and the face. Works.

  4. efix2 | Dec 28, 2005 03:15am | #8

    Just to add to the confusion:    LOL

    Whenever I install a union I take it apart first and check for dings on the mating surfaces.  If in doubt I hit it with a swipe of sandpaper (which I have out anyways).  Only takes a sec.

  5. User avater
    xxPaulCPxx | Dec 28, 2005 04:11am | #9

    I just repiped my garage, and used 8 unions - 5 were 3/4" and 3 were 1/2".  I used the yellow Rector thread sealent, and only one leaked.  The leaking one was a very slow drip, and was fixed by tightening it a little more.

    It is very important to lubricate any fastener that has two theaded parts, like a bolt and nut or a pipe union.  The lubrication ensures that the metals don't gall and they achieve a more uniform torque.

    Rebuilding my home in Cypress, CA

    Also a CRX fanatic!

  6. 4Lorn1 | Dec 28, 2005 04:15am | #10

    Re: " I have tried to tighten them without ruining the sealing face."

    Seems to me, based on what little I have gathered from plumbers, that you may not have them tight enough. These units take a whole lot of torque to make up permanently. Especially as they get larger. IMHO much more than most other fittings and more than most people think. Two long wrenches applied like you had OBL by the nuts.

    Yelling 'I want to hear you scream.' while you work the wrenches helps. Also helps eliminate unnecessary interruptions and complaints. 'I love my job. I am well paid' is also an option. Whatever works for you.

    I wouldn't worry too much about over tightening as long as the wrenches are properly adjusted and don't slip or distort the fitting. Make sure you get a good three-point contact on a pipe wrench to prevent excessive distortion. Up side if they fail they needed replacing anyway.

  7. plumbbill | Dec 28, 2005 07:03am | #11

    OK are they copper to copper unions?

    Or are they die electric unions?

    copper to copper is not a test of strength putting them together a small bur can drip really easy. Yes use a dope of some sort on the threads to lubricate (not seal) when assembling.

    Some emery cloth on face is a good idea but don't go overboard.

    If everything is right you should not have any leaks. Then again this is not a perfect world.

    Putting dope on mating surface will usually seal it -------but when the dope eventually washes out it will leak again.

Log in or create an account to post a comment.

Sign up Log in

Become a member and get full access to FineHomebuilding.com

Video Shorts

Categories

  • Business
  • Code Questions
  • Construction Techniques
  • Energy, Heating & Insulation
  • General Discussion
  • Help/Work Wanted
  • Photo Gallery
  • Reader Classified
  • Tools for Home Building

Discussion Forum

Recent Posts and Replies

  • |
  • |
  • |
  • |
  • |
  • |
View More Create Post

Up Next

Video Shorts

Featured Story

The Trump Administration Wants to Eliminate the Energy Star Program

The end of this program will likely lead to higher energy bills and fewer business opportunities for the American people.

Featured Video

SawStop's Portable Tablesaw is Bigger and Better Than Before

The 10-in. Jobsite Saw PRO has a wider table, a new dust-control port, and a more versatile fence, along with the same reliable safety mechanism included in all SawStop tablesaws.

Related Stories

  • A Summer Retreat Preserved in the Catskill Mountains
  • Fine Homebuilding Issue #332 Online Highlights
  • The Trump Administration Wants to Eliminate the Energy Star Program
  • Podcast Episode 685: Patching Drywall, Adding Air Barriers, and Rotted Walls

Highlights

Fine Homebuilding All Access
Fine Homebuilding Podcast
Tool Tech
Plus, get an extra 20% off with code GIFT20

"I have learned so much thanks to the searchable articles on the FHB website. I can confidently say that I expect to be a life-long subscriber." - M.K.

Get home building tips, offers, and expert advice in your inbox

Signing you up...

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
See all newsletters
See all newsletters

Fine Homebuilding Magazine

  • Issue 331 - June 2025
    • A More Resilient Roof
    • Tool Test: You Need a Drywall Sander
    • Ducted vs. Ductless Heat Pumps
  • Issue 330 - April/May 2025
    • Deck Details for Durability
    • FAQs on HPWHs
    • 10 Tips for a Long-Lasting Paint Job
  • Issue 329 - Feb/Mar 2025
    • Smart Foundation for a Small Addition
    • A Kominka Comes West
    • Making Small Kitchens Work
  • Issue 328 - Dec/Jan 2024
    • How a Pro Replaces Columns
    • Passive House 3.0
    • Tool Test: Compact Line Lasers
  • Issue 327 - November 2024
    • Repairing Damaged Walls and Ceilings
    • Plumbing Protection
    • Talking Shop

Fine Home Building

Newsletter Sign-up

  • Fine Homebuilding

    Home building tips, offers, and expert advice in your inbox.

  • Green Building Advisor

    Building science and energy efficiency advice, plus special offers, in your inbox.

  • Old House Journal

    Repair, renovation, and restoration tips, plus special offers, in your inbox.

Signing you up...

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
See all newsletters

Follow

  • Fine Homebuilding

    Dig into cutting-edge approaches and decades of proven solutions with total access to our experts and tradespeople.

    Start Free Trial Now
    • Facebook
    • Instagram
    • X
    • LinkedIn
  • GBA Prime

    Get instant access to the latest developments in green building, research, and reports from the field.

    Start Free Trial Now
    • Facebook
    • YouTube
  • Old House Journal

    Learn how to restore, repair, update, and decorate your home.

    Subscribe Now
    • Facebook
    • Instagram
    • X
  • Fine Homebuilding

    Dig into cutting-edge approaches and decades of proven solutions with total access to our experts and tradespeople.

    Start Free Trial Now
    • Facebook
    • Instagram
    • X
    • LinkedIn
  • GBA Prime

    Get instant access to the latest developments in green building, research, and reports from the field.

    Start Free Trial Now
    • Facebook
    • YouTube
  • Old House Journal

    Learn how to restore, repair, update, and decorate your home.

    Subscribe Now
    • Facebook
    • Instagram
    • X

Membership & Magazine

  • Online Archive
  • Start Free Trial
  • Magazine Subscription
  • Magazine Renewal
  • Gift a Subscription
  • Customer Support
  • Privacy Preferences
  • About
  • Contact
  • Advertise
  • Careers
  • Terms of Use
  • Site Map
  • Do not sell or share my information
  • Privacy Policy
  • Accessibility
  • California Privacy Rights

© 2025 Active Interest Media. All rights reserved.

Fine Homebuilding receives a commission for items purchased through links on this site, including Amazon Associates and other affiliate advertising programs.

  • Home Group
  • Antique Trader
  • Arts & Crafts Homes
  • Bank Note Reporter
  • Cabin Life
  • Cuisine at Home
  • Fine Gardening
  • Fine Woodworking
  • Green Building Advisor
  • Garden Gate
  • Horticulture
  • Keep Craft Alive
  • Log Home Living
  • Military Trader/Vehicles
  • Numismatic News
  • Numismaster
  • Old Cars Weekly
  • Old House Journal
  • Period Homes
  • Popular Woodworking
  • Script
  • ShopNotes
  • Sports Collectors Digest
  • Threads
  • Timber Home Living
  • Traditional Building
  • Woodsmith
  • World Coin News
  • Writer's Digest
Active Interest Media logo
X
X
This is a dialog window which overlays the main content of the page. The modal window is a 'site map' of the most critical areas of the site. Pressing the Escape (ESC) button will close the modal and bring you back to where you were on the page.

Main Menu

  • How-To
  • Design
  • Tools & Materials
  • Video
  • Blogs
  • Forum
  • Project Guides
  • Reader Projects
  • Magazine
  • Members
  • FHB House

Podcasts

  • FHB Podcast
  • ProTalk

Webinars

  • Upcoming and On-Demand

Podcasts

  • FHB Podcast
  • ProTalk

Webinars

  • Upcoming and On-Demand

Popular Topics

  • Kitchens
  • Business
  • Bedrooms
  • Roofs
  • Architecture and Design
  • Green Building
  • Decks
  • Framing
  • Safety
  • Remodeling
  • Bathrooms
  • Windows
  • Tilework
  • Ceilings
  • HVAC

Magazine

  • Current Issue
  • Past Issues
  • Magazine Index
  • Subscribe
  • Online Archive
  • Author Guidelines

All Access

  • Member Home
  • Start Free Trial
  • Gift Membership

Online Learning

  • Courses
  • Project Guides
  • Reader Projects
  • Podcast

More

  • FHB Ambassadors
  • FHB House
  • Customer Support

Account

  • Log In
  • Join

Newsletter

Get home building tips, offers, and expert advice in your inbox

Signing you up...

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
See all newsletters
See all newsletters

Follow

  • X
  • YouTube
  • instagram
  • facebook
  • pinterest
  • Tiktok

Join All Access

Become a member and get instant access to thousands of videos, how-tos, tool reviews, and design features.

Start Your Free Trial

Subscribe

FHB Magazine

Start your subscription today and save up to 70%

Subscribe

Enjoy unlimited access to Fine Homebuilding. Join Now

Already a member? Log in

We hope you’ve enjoyed your free articles. To keep reading, become a member today.

Get complete site access to expert advice, how-to videos, Code Check, and more, plus the print magazine.

Start your FREE trial

Already a member? Log in

Privacy Policy Update

We use cookies, pixels, script and other tracking technologies to analyze and improve our service, to improve and personalize content, and for advertising to you. We also share information about your use of our site with third-party social media, advertising and analytics partners. You can view our Privacy Policy here and our Terms of Use here.

Cookies

Analytics

These cookies help us track site metrics to improve our sites and provide a better user experience.

Advertising/Social Media

These cookies are used to serve advertisements aligned with your interests.

Essential

These cookies are required to provide basic functions like page navigation and access to secure areas of the website.

Delete My Data

Delete all cookies and associated data