Teflon tape or liquid thread sealant?

[thedcdude]

Just wondering what professional plumbers prefer to seal threaded couplings. (and why)

[LazyPup]

Per ASTM (American Society of Testing & Materials) specifications all NPT (National Pipe Taper) thread joints require a sealant to complete the joint. The choice of sealing material is then dictated by the product that will be conveyed in the pipe.

In the residential enviroment the types of materials conveyed in the pipes is primarily limited to Potable water, Non-Potable water, Natural Gas, Liquified Petroleum Gas (LP gas), Fuel Oil and on rare occassions compressed air in a home shop. Within this limited range of application both PTFE(teflon) tape and even the less expensive pipe dopes will generally meet the need so it then becomes a matter of personal preference by the individual installer.

I like to think of residential threaded joints as permanent joints to which I apply pipe dope or semi-permanent joints upon which I commonly use tape.

A permanent joint is any joint which would normally be installed during the rough-in or stack-out phase of the plumbing and which could be reasonably epected to last the lifetime of the structure. These would include galvanized iron water lines, threaded connections on main & zone valves on the water distribution system and gas lines.

Semi-permanent joints are those which we typically make during the final trim out phase such as fixture angle stops, shower arms, shower heads, tub spout to the stub outs or any joint which we could reasonably expect may be changed periodically for general maintenance or aestetics purposes during the life of the structure.

No discussion of Teflon tape would be complete without discussing the different grades of teflon tape as well.

While it is not commonly known by the general public the ASTM has issued some rather strict specifications concerning the different grades of teflon tape and their approved application. They have also now instituted a color coding system to insure we use the correct grade of teflon tape.

WHITE- Single density PTFE tape- When teflon tape first came on the market the white single density tape was the only one available and was generally considered suitable for all applications. They later came out with a double density white tape but it was primarily only distributed through commercial plumbing & HVAC supply houses so the general public was not aware of it.

Many codes then required double density tape be used on all gas lines however considering that both grades were white it was difficult for inspectors to visually determine which grade had actually been used. In response to that the ASTM then instituted a specification which required all double density tape should be Yellow for easier identification. We often see the Yellow Double density tape labelled as "Gas Tape".

The ASTM has now broadened the specifications for PTFE tape:

WHITE- single density- may only be used on NPT threads not to exceed 3/8".

YELLOW -Double Density- May continue to use on gas lines where approved by local code.

RED Triple Density- may be used on all NPT joints up to 2". (Currently required for domestic water distribution lines greater than 3/8").

GREEN- Certified oil free- may be used on oxygen lines.

Copper- Not certified as a thread sealant, contains copper granules and may be used as a thread lubicant only.

Teflon tape is only certified if applied in the prescribed manner. Three full wraps must be applied under tension and must be wrapped in the direction of rotation of the threads.

Now getting back to the original question, what do the pro's prefer?

My personal preference is a product called "Rector Seal"

Rector Seal #7 is nearly a universal pipe dope that is certified for use on Aromatic solvents, Dilute Caustics, Concentrate caustics, Chlorinated solvents, Cutting oils, diesel fuel, ethylene glycol, liquid fatty acids, gasohol (unleaded 10% alcohol), gasoline, glycerine, heating oils, helium gasses, hydraulic oil, hydraulic fluids, hydrogen gaseous, inert gasses, Jet fuel (JP3,4 &5), kerosene, ketones, liquified petroleum gase (LP gas), mineral oils, natural gas, nitrogen gasseous, petroleum solvents, refrigerants, refrigeration oil, liquid soap, steam, vegetable oil and Potable water (both hot & cold).

[thedcdude]

Thanks for such a complete answer.
What would you use on threaded PVC drain fittings?

[LazyPup]

For new construction there are no NPT threaded fittings in the DWV (Drain,waste & Vent) system with the singular exception of cleanout caps or perhaps an air admittance valve.

Back in the days of cast iron pipe with leaded joints they often used galvanized iron pipe to make fixture drains under 2" diameter and many cast iron tee's had a threaded hub to accept the iron pipe. When reworking those systems we often remove the galvanized iron pipe and replace it with PVC. In this case we would use a PVC male thread adapter to connect to the cast iron hub and we could use teflon tape or pipe dope. Here again, this could be thought of as a permanent joint so I prefer to use dope.

The PVC Trim out fittings such as tailpieces, tailpiece extensions, End waste or center waste kits, P-traps and trap adapters all use a compression fitting. The compression fittings all seal by means of an internal plastic ferrule and you should not apply any teflon tape or dope to these fittings because it would interfere with the designed sealing mechanism.