To prevent leaks and keep your plumbing system running longer, it’s important to properly seal your threaded plumbing connections. From tapered threads to Teflon tape, different connection types require specific sealants and techniques to create watertight seals. In the video above, This Old House plumbing and heating expert Richard Trethewey showcases the proper techniques for sealing different plumbing connections.
Types of Threaded Plumbing Connection
There are two main types of threaded connections used in plumbing: tapered threads and straight threads. Each type requires a different sealing approach.
Tapered Threads
Tapered threads are the most common type of plumbing connection. These threads become progressively smaller in diameter as they approach the end of the fitting. This design allows for a tighter seal as the fitting screws into place.
Tapered threads are typically found in connections that require a strong, leak-proof seal. They are especially common in older systems with metal piping. Using the proper sealant with these threads is important to help the seal remain intact under various pressure and temperature conditions.
Straight Threads
Straight threads maintain a consistent diameter along their length. They are typically used in conjunction with other sealing methods, such as gaskets or O-rings, to create a watertight connection. Unlike tapered threads, straight threads do not naturally tighten as they are screwed in, so additional sealing components are necessary.
These threads are common in modern plumbing systems, particularly with plastic and metal fixtures that need to be periodically replaced or serviced.
Types of Plumbing Sealants
There are several sealant types used in plumbing connections.
Teflon Tape
Teflon tape, also known as plumber’s tape or thread seal tape, is a popular choice for sealing threaded connections. It’s easy to apply, inexpensive, and effective for many types of fittings. Due to its nonreactive nature, Teflon tape is particularly useful for plastic connections.
Pipe Dope
Pipe dope, or pipe thread sealant, is a paste-like substance that binds to threads to create a watertight seal. It’s useful for metal fittings and often combined with other sealing methods. Pipe dope provides a more durable seal than Teflon tape, making it suitable for high-pressure applications.
Wicking
Wicking is a traditional method that uses a string-like material to fill the gaps between threads. It’s often used in combination with pipe dope for a more secure seal, especially on older fittings. The wicking material expands when it comes into contact with moisture, providing additional protection against leaks.
Anaerobic Sealants
Anaerobic sealants are typically used in high-pressure and high-temperature applications. These sealants cure in the absence of air, forming a solid plastic-like material that fills the gaps between threads. They’re ideal for metal-to-metal connections but should be used with caution, as they can form a permanent bond that’s hard to break.
When To Use Teflon Tape for Plumbing Connections
Teflon tape is a great choice for many plumbing connections, particularly those involving plastic fittings. Here’s how to apply it properly:
- Clean the threads thoroughly to remove any dirt or debris.
- Hold the fitting in your left hand (for right-handed individuals).
- Start at the end of the fitting and wrap the tape clockwise around the threads.
- Overlap each turn slightly, wrapping two to three times around the fitting.
- Pull the tape tight and break it off, pressing the end firmly against the threads.
Teflon tape is ideal for connections that may need to be disassembled in the future, as it doesn’t harden or create a permanent bond. It also offers some lubricating properties, making it easier to assemble and disassemble connections without damaging the threads.
Teflon tape should not be used on gas connections unless it’s rated specifically for that purpose. Always check the packaging for the tape’s intended use.
When To Use Pipe Dope for Plumbing Connections
Pipe dope is effective for metal tapered fittings. It fills the gaps between threads and creates a strong seal. Here’s how to apply pipe dope:
- Clean the threads thoroughly.
- Apply a thin, even coat of pipe dope to the male threads using a brush or applicator.
- Spread the sealant evenly around the entire circumference of the threads.
- Assemble the joint, tightening it securely.
Pipe dope is great for connections that may be subject to vibration or temperature changes, as it remains somewhat flexible after application. It’s also good for metal connections because it provides a more substantial seal compared to Teflon tape.
When To Use Wicking for Plumbing Connections
Wicking works well with pipe dope and is useful for connections that have proven difficult to seal. The string-like material used in wicking can enter the smallest of gaps, providing an additional barrier against leaks. Here’s how to use wicking properly:
- Apply pipe dope to the threads as described above.
- Lay a single strand of wicking material into the threads, following their spiral pattern.
- Apply another thin layer of pipe dope over the wicking.
- Assemble the joint, tightening it securely.
Wicking is particularly effective for older fittings or those that have been problematic.
Combining Plumbing Sealant Methods
In some cases, combining sealant methods can provide extra protection against leaks. One effective combination is using pipe dope with Teflon tape or wicking. Here’s how:
- Apply pipe dope to the threads as described above.
- If using wicking, lay a single strand of wicking material into the threads.
- Wrap Teflon tape over the pipe dope and wicking–if applicable.
- Assemble the joint, tightening it securely.
Always make sure that the components used are compatible and appropriate for the application.
Special Considerations for Different Plumbing Connection Types
Not all plumbing connections require the same sealing method. Here are some special cases to keep in mind.
Ground Joint Connections
Ground joint connections, such as those found on some radiator valves, require a different approach.
- Apply a small amount of pipe dope to the unthreaded portion of the joint where the two surfaces meet.
- Do not apply any sealant to the straight-threaded portion of the connection.
- Tighten the connection securely to create a seal between the two ground surfaces.
Ground joint connections rely on the mating surfaces to form a seal. Applying pipe dope to the unthreaded portion can help provide a tight fit, but using it on the threads can interfere with the sealing surfaces.
Connections with Rubber Gaskets
Some modern faucet connections come with built-in rubber gaskets. For these connections, do the following:
- Do not apply any sealant to the threads.
- Simply tighten the connection enough to compress the rubber gasket against the mating surface.
- Be careful not to overtighten, as this can damage the gasket.
Rubber gaskets provide a watertight seal without the need for additional sealants. However, it’s important to make sure the gasket is properly aligned and not damaged during installation.
Compression Fittings
Compression fittings are common in various plumbing applications, including water supply lines and shut-off valves. These fittings use a compression nut and ferrule to create a seal. For these connections, do the following:
- Slip the compression nut onto the pipe.
- Place the compression ring over the pipe.
- Insert the pipe into the fitting and tighten the compression nut onto the fitting.
Do not use any sealant on compression fittings, as the compression ring creates the seal. Overtightening can deform the ring and cause leaks.
Common Plumbing Connection Mistakes to Avoid
When sealing threaded plumbing connections, be aware of these common pitfalls:
- Overtightening connections, which can damage threads or crack fittings
- Using the wrong sealant for the material or connection type
- Applying sealant to the female threads instead of the male threads
- Using too much sealant, which can interfere with proper thread engagement
- Failing to clean threads before applying sealant
Understanding these common mistakes can help you avoid potential issues.
