Per ASTM (American Society of Testing & Materials) Standards, a DIYer must use a thread sealant on all NPT (National Pipe Taper) threads & fittings.
The type of thread sealant is selected for compatibility with the material that the DIYer will be using.
In a typical DIYer setting, the use of NPT joints is to seal pipes for water, natural gas, propane gas, #1 & #2 heating oils and occasionally low pressure steam, refrigerants or high-pressure air in a shop compressor system.
PTFE OR TEFLON TAPE
When a thread seal tape was first introduced, it only came in a single density type (“white teflon tape”) that was commonly found in large home improvement stores. Later they began making a double density version, which was twice as thick in the same color (unfortunately with the same “white” color).
Please note very carefully that is says “Pipe Thread Tape”. PTFE Tape and “Pipe Joint Compounds” are to be used only on NPT (National Pipe Taper) male threads. Neither PTFE nor Pipe Joint Compound are to ever be used on SAE mechanical threads or as a gasket sealer such as for the sink basket gasket as was suggested above and absolutely nothing is to be applied to the threads on the PVC slip type DWV fittings such as P-traps, tailpieces, Waste & Overflow Kits, End Waste kits or Center Waste kits.
TEFLON TAPE COLORS
Since many state and local codes adopted the use of double density tapes when making connections for natural gas, the use of same color for two different thickness presented a challenge when time came to inspect a job. Thus, a “yellow teflon tape” was later introduced for such application.
Since then, PTFE tape is now made in numerous varieties and they have issued a color standard to determine which type should be used:v
- White- single density, should only be used on NPT threads up to 3/8 inch in diameter.
- Yellow – double density, often labeled as “gas tape”
- Red of Pink – triple density, required on all joints 1/2″ or larger.
- Green – oil Free PTFE tape, required for use on all lines carrying oxygen (i.e. – medical oxygen or welding oxygen lines).
THREAD TAPE APPLICATION
PTFE tape is only approved as a thread seal when applied correctly.
It is very important to apply the tape from the end of the pipe and wrap the tape under tension in the direction of the thread turns. Each successive layer should overlap the previous layer by approximately 1/2 to 2/3 in width and continue wrapping until the entire threaded portion of the pipe is covered (in general, full 3 revolutions or turns is sufficient).
THINGS TO REMEMBER WHEN APPLYING THREAD SEAL TAPE
- The main purpose of a thread seal tape is to seal out micro abrasions or surface irregularities on threads. If you have a major gash or nick on a thread, replace the pipe section or re-thread it, rather than applying a thicker seal tape layer.
- Appying more than 3 layers is not recommended
- When starting out, make sure the seal tape is not covering the pipe opening. Any exposed seal tape may break loose over a period of time and cause a blockage problem
- Pipe connections generally turn clock-wise but there are instances when that is not true (i.e. gas pipe union joint). Always test out and make a note of the pipe rotation before applying the tape and remember that the tape application must “go with the flow”.
When looking for pipe dope in the hardware or home supply store we commonly find two types:
- “pipe dope” – a dark gray paste (Oatey 15420 Pro Dope);
- “teflon pipe dope” – a white paste (Rectorseal 25631Pipe Thread Sealant).
Whether you choose Oatey or RectorSeal, they come in wide variety so make sure to check the directions as well as MSDS (material safety data sheet) to fully understand and verify that the product you intend to buy is listed as approved application for your project.
WHICH TO USE?
Providing the teflon tape, ppipe dope or teflon pipe dope is approved for the type of material you intend to use in the pipe thread, the choice largely a matter of personal preference (teflon tape is lot less messy than either pipe or teflon dopes).
Though I have used teflon tape and pipe dope in combination in the past but I no longer do so because I believe it to be unnecessary (much like applying black tape to electrical wire connections).
Although there is no hard and fast rule, most plumbers I have used in the past seem to prefer to use teflon pipe dope on all permanent pipe joints (i.e. gas pipe fittings to a water heater) whereas teflon tape is often used in faucet stop valves, showerhead, etc.
While there is a number of universal pipe dopes on the market, the one that is most widely accepted by plumbers, pipe fitters, HVAC techs and electricians is a product called “RectorSeal”.
While other pipe dopes are may be listed for a broad range of applications RectorSeal is listed as approved for but not limited to, Potable water, non-potable water, DWV, Natural Gas, propane, fuel oils (#1 through heavy bunker oils), gasoline, kerosene, diesel fuel, motor oils, lubricants, aviation fuel, jet fuel, high & low pressure air, low pressure steam, high pressure steam, most refrigerants, numerous industrial chemicals, most agricultural fertilizers and electrical conduits in both above grade and direct burial applications.
For a comprehensive thread sealant product matrix, click here
Although RectorSeal is seldom found in a home improvement store, it can be found in almost all plumbing supply houses and online stores.
Petroleum-based pipe dope like Oatey’s 1540 Pro Dope, is *not* intended for use on threaded PVC, CPVC or ABS pipe and fittings since it will deteriorate the plastic.
For these composite materials, products that meet ASTM F2331 (Standard Test Method for Determining Chemical Compatibility of Thread Sealants with Thermoplastic Threaded Pipe and Fittings Materials) or thread seal tape should be used.
But in my experience, I found that threads on composites materials do a superior job of sealing when compared to metal based threads so I have yet to use any thread tapes or sealants on them.
One thing to keep in mind is that my experience is based on low to no pressure connections (sink drain, DWV, etc.) so if you are using one of the in a pressurized setting, you probably should use a locking sealant.