Thread Sealants 101

By Sean Comerford

Threaded pipe joints may seem straightforward, but leaks are almost guaranteed without the right thread sealant and proper technique. Whether swapping out a shower head, connecting a water heater, or repairing gas lines, knowing when and how to use thread sealants can save time, prevent leaks, and avoid costly damage.

In this guide, we’ll discuss key principles of thread sealants: options, how they work, why threads fail, application tips, and how to choose the proper sealant for your job.

Thread sealants come in various forms, each suited to specific materials, system pressures, and environmental conditions. You'll find an extensive range of NSF-approved thread sealants that are safe for potable water and engineered to meet rigorous performance standards.

Pipe Joint Compounds

Pipe joint compounds (also known as pipe dope) offer reliable sealing with formulations suited for different materials and temperatures. Note that all compounds from Oatey and Hercules, excluding Hercules Brush-on Block, are NSF-certified, ensuring safety for drinking water systems.

Popular options include:

●        Hard Set formulations like Hercules Grrip: This thread sealant sets up quickly and dries to form a very tough, yet flexible seal, replacing the need for a traditional gasket and making it ideal for systems requiring flat, metal-to-metal connections.

●        Soft Set formulations like Oatey Great Blue Pipe Joint Compound: This compound is a non-separating thread sealant formulated to seal threaded connections on metal and plastic pipe up to 2 inches in diameter. Its uniform, smooth consistency allows easy application on lines carrying water, natural gas (except oxygen), steam, air lines, caustics, and dilute acids.

●        PTFE-based formulations like Hercules Real Tuff use a unique system of fine-grain PTFE particles to fill cracks and thread imperfections. Designed for high-pressure applications, this smooth-setting sealant forms durable, leak-free seals so that joints can be tested and put into service immediately. Used on lines carrying water, steam, caustics, and dilute acids, it is compatible with all metals plus PVC, CPVC, and ABS plastics.

●        FBC^™ approved (third party tested) products like Oatey Great White Pipe Joint Compound With PTFE. These sealants are safe for CPVC systems (e.g., FlowGuard^®, BlazeMaster^®, Corzan^®).

Thread Sealant Tape

Teflon tape is a chemically inert, flexible film wrapped around male threads to help fill the gaps between threads and prevent leaks. It’s clean, quick to apply, and ideal for smaller-diameter fittings or when a mess-free solution is needed.

Thread tapes are distinguished by color, thickness, density, and width. Each is optimized for specific applications:

• White tape: General-purpose, three mil thick, high-density, and compatible with most pipe materials. It can be used with plastic, copper, aluminum, galvanized steel, or black iron piping.

• Pink tape: Full-density, suitable for air, water, sewage, and hydraulic systems up to 1-1/2 inches.

• Yellow tape: 3.5 mil thick, ideal for natural gas piping.

Local municipalities may require specific colors for each application to ensure proper identification.

For added versatility, Hercules Megatape is a standout:

• High-density, 3.5 mil thick.

• Resists tearing on harder, sharper threads.

• Available in gray, a more aesthetically pleasing choice for chrome/nickel fixtures.

• Offered in standard and extra-large spools.

While both types of thread sealant are effective, the choice depends on fixture type, thread size, material compatibility, and personal preference.

Pro Tip: For fittings 1-1/4-inch and larger under pressure, using both types together—tape first, followed by compound—is recommended for a more secure seal. Ultimately, using either or both depends on the specific demands of the job. Combining them can provide added security.

How Thread Sealants Work And Why They Fail

Most plumbing threads follow the NPT (National Pipe Thread) standard. These threads are tapered, which means the male and female parts wedge together as they tighten.

In theory, that taper should create the seal. In practice, imperfections and roughness in the threads leave pathways for leaks.

Sealants fill those gaps and compact into the threads as the joint is tightened.

Causes of sealant failure may include:

• Bad threads: Corroded or chipped threads create leak paths. Application of new sealant can sometimes salvage old fittings when replacement isn’t practical (like inside walls).

• Insufficient or incorrect application: Using too little compound, brushing with the threads instead of against them, or wrapping tape counterclockwise can all compromise the seal.

• Overuse of tape: More isn’t always better. Too many wraps can stress female fittings, sometimes causing hairline cracks that appear months or years later.

• Incompatible materials or contents: Certain compounds can weaken plastics such as CPVC or deteriorate when exposed to oils, chemicals or fuels.

  
  

When to Use Thread Sealant

Thread sealants play a critical role in various household plumbing applications where threaded joints connect fittings and components. A sealant is almost certainly required in typical home settings.

DIY repair involves water lines or drains with threaded connections, especially in older homes with galvanized or cast iron pipes.

Common examples include:

• Threaded shower arms

• Water valves for toilets and dishwashers

• Where a pipe exits a wall

  
  

Users frequently apply a light coating for added security even when dealing with compression fittings, which technically don’t need sealant.

Always use thread sealant on any threaded connection without a built-in gasket, washer, or O-ring. Even when washers are present, plumbers often still apply sealant for extra protection.

Outdoor plumbing fixtures like hose bibs and splitters may also benefit from sealant use in installations lacking rubber washers. In warmer regions where outdoor plumbing is more common, such as California, you might encounter threaded joints on external tankless water heaters or supply control valves.

Gas, steam, or high-pressure threaded systems are also suitable applications.

There are exceptions where sealant should not be used:

• Female threads: NPT threads are tapered; any sealant applied here will get pushed into the system during assembly.

• Push-fit or compression fittings: These seal mechanically. While plumbers sometimes apply a light coat out of habit, it isn’t necessary.

• Fixtures with manufacturer restrictions: For example, flush valves or certain ice maker lines may specify no tape/dope, since material could break loose and clog components.

• Systems carrying incompatible chemicals: Always verify against product submittal sheets.

Choosing the Right Thread Sealant

The proper thread sealant is key to ensuring safe, leak-free, and long-lasting connections. The right product depends on system temperature, pressure, material compatibility, and fluid or gas type. Safety is paramount in potable water systems. To prevent contamination, only NSF/ANSI 61-certified sealants should be used.

Soft-set sealants are preferred for water systems due to their flexibility and ease of disassembly. Megaloc is a versatile, user-friendly option compatible with CPVC piping. Sealants must tolerate extreme conditions in steam or high-pressure applications.

Megaloc with DuPont^™ Kevlar is rated from -50°F to 400°F and can handle pressures up to 2,600 pounds per square inch (PSI) for gas and 12,000 PSI for liquids. It stays flexible without cracking and remains brushable even in cold weather down to -25°F.

Material compatibility is also critical. Thread tapes can be used with nearly all pipe types, while compounds are approved for materials like aluminum, copper, brass, stainless steel, galvanized and black iron, PVC, CPVC, polyethylene, polypropylene, and even glass.

However, not all compounds work with every fluid or gas. Always check chemical compatibility, using manufacturer submittal sheets—especially for natural gas, propane, glycol, heating oils, and acids.

Some systems require FBC^™-approved products, particularly CPVC-based piping like FlowGuard^®, BlazeMaster^®, and Corzan^®. Oatey Great White and Hercules Pro Dope are both FBC-approved and safe for long-term CPVC use.

Professionals often use thread sealant tape and compound for added security in larger or high-stress systems. Oatey recommends this dual method for pipe sizes 1-1/4-inch and above.

When selecting tape, keep in mind:

• Width: Available in 1/2-inch, 3/4-inch, and 1-inch.

• Thickness: Thicker tapes (e.g., 3.5 mil) reduce wrap count.

• Density: Higher density minimizes stretch and leak risk.

  
  

Hercules Megatape is a high-performance option with superior strength and aesthetics—particularly useful on chrome or nickel fixtures.

Ultimately, the right sealant ensures jobsite efficiency, code compliance, and long-term peace of mind. Always refer to the manufacturer’s technical sheets for the best match to your application.

7 Tips To Apply Thread Sealants Like A Pro

1.       Wrap clockwise: Always apply thread sealant tape in a clockwise direction when facing the male threads because wrapping counterclockwise will unravel when tightening.

2.       Three to five wraps are enough: Adjust based on tape density (fewer wraps for thicker products like Megatape^™).

3.       Leave the last thread bare: This prevents sealant from being pushed into the system, where it could clog aerators or filters.

4.       Brush compound against the threads: This forces sealant into the thread roots instead of skimming the surface.

5.       Apply only to male threads. Female threads rely on taper fit, and adding compound there can interfere with sealing.

6.       Avoid over-tightening: Compounds act as lubricants, making overtightening a risk. Tighten firmly but not excessively.

7.       Consider temperature: Most compounds apply fine to 20°F, but Megaloc remains workable to -25°F for cold-weather repairs.

Final Takeaway

Thread sealants aren’t just an afterthought. They’re the difference between a dry, reliable system and a hidden leak waiting to surface.

For DIY'ers, knowing the basics of how sealants work, choosing the right product, and applying it correctly makes every repair safer and more durable. Stick to NSF- and FBC-approved products, match sealant type to the job, and remember: Less is often more.

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About the author: Sean Comerford is Manager, Inside Sales and Tech Support at Oatey Co. He is a third-generation tradesman with nearly 20 years of plumbing experience, including the lead plumber for commercial/residential new-construction, service and fire protection jobs. He holds a State of Ohio Fire Protection License for Sprinkler and Standpipe.