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How To Seal A Cast Iron Pipe Joint Using Oakum And Silicone Grease

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A common way for do-it-yourself homeowners to seal iron pipe threads is the use of plumbers tape. Also commonly called Teflon tape, thread seal tape and PTFE tape, plumbers tape is relatively easy to use and inexpensive. However, its effectiveness decreases as the diameter of the pipe increases, and this can result in leaks. Most do-it-yourselfers don't realize there is an alternative to plumbers tape, and that is the use of oakum and plumbers grease. This time-honored method of sealing iron pipe threads is resistant to leaks and can be used with any size of threaded pipe. If you are a do-it-yourselfer installing cast iron pipe, especially pipe that is an inch in diameter or more, then keep reading on how to use oakum and grease:

What you will need

You can purchase these an other plumbing supplies from a local hardware store or online through sites like http://www.centralplumbingspec.com.

  • Oakum - Sold by plumbing suppliers and online retailers, this hemp-fiber material comes in small bundles and is also used in the marine industry for waterproofing propeller shafts.

  • Plumbers silicone grease - Be sure the grease you purchase is appropriate for use with your particular application and environment; some greases are not suitable for use in high temperatures, for example.

  • Utility knife

  • Pipe wrench

  • Wire brush

  • Mineral spirits

  • Cloth

Step-by-step procedure

1. Thoroughly clean the pipe threads - Before joining the pipe, it is important to clean the threads to ensure the oakum and grease will adhere. Take a wire brush and vigorously scrub the threads to remove debris; if the threads are exposed to oil or other liquids, clean them with mineral spirits and allow the threads to air dry.

2. Apply a thin layer of plumbers grease - Squeeze out a small dab of grease on your fingers and smear it around the threads. Be sure to push the grease deep into the threads, but keep the layer about 1/16th of inch thick. Try to avoid getting grease into the opening of the pipe, and wipe away any spills with a cloth.

3. Unravel the oakum to form fibers - Take about 6 inches of oakum in your hand, then begin twisting it between your thumb and forefinger to unravel the individual fibers. Next, pull out the fibers with your other hand until you have a thin, loose bundle of fibers in your hand. Don't worry if some of the fibers break or pull apart; they can be patched together when you wrap them around the threads.

4. Wrap the threads with oakum fibers - Once the oakum is unraveled, lay the loose bundle of fibers across the threads in a 45-degree angle. Next, begin slowly wrapping the fibers around the threads in a clockwise direction while continually pushing them into the grease. Distribute the fibers evenly over and around the threads until each thread has been filled. However, do not allow the fibers to extend past the end of the pipe, so cut away excess fibers with a utility knife. Continue to "work" the grease until it is smooth and mostly covers the fibers. If necessary, add a small amount of grease to cover any bare spots.

5. Join the pipes together - After you have finished adding the oakum fibers and grease to the pipe threads, join the pipe ends together and begin to turn the pipe by hand to engage the threads. Watch the threads to be sure an excessive amount of oakum and grease doesn't push out of the end of the joint; if it appears that most of the material is pushed from the joint, unscrew the pipe and repack the threads. Once you are no longer able to turn the pipe by hand, use a pipe wrench to continue turning the pipe until the joint is tight.

6. Remove excess oakum and grease - When you have finished tightening the joint with the pipe wrench, use a sharp utility knife blade to trim the excess oakum away from the backside of the joint. Wipe it clean with a cloth to remove the remaining material.


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