Pipe joint compound, or pipe dope, and plumbers putty are sometimes confused as the same product or intended for similar uses. However, the two are very different in both appearance and application. While both provide a seal against leaks in various types of piping systems, plumbers putty and joint compound have characteristics that make them suitable for different applications.
Plumbers putty has the consistency of silly putty and acts similar to a gasket on connections like sink drains where no water pressure is present. Pipe joint compound is typically a thin liquid used by plumbers to prevent leaks in threaded pipe connections. It works similar to Teflon tape, and provides protection against friction between the pipes and fills the cavities between the pipe threads to form a watertight seal.
A major difference between plumbers putty and joint compound is the intended use for each. Plumbers putty is used to seal joints in a similar way that a gasket would and can be used to seal metal, PVC and ceramics. It is paintable and used around the home for sealing sink and drain basket joints, but may also be used on gutters and down-pipes and on sanitary joints that are vulnerable to vibration or movement. It is intended to provide a seal against leaks in situations where pressure is not a factor.
Pipe joint compound is available in different formulations which depend on the type of pipe and the material it is carrying. These formulations may be used on aluminum, iron, steel, brass and copper pipes and is used as a bonding agent to provide a leak-proof seal in threaded plumbing pipe applications. Joint compound may also be used in pipes that carry acids, air, gas, oils and water.
The primary benefit of plumbers putty is its ease of use. Flexible and non-cracking plumbers putty is also non-toxic, making it safe to use in your home. Excess putty can be quickly cleaned away with water and it forms a fast seal. Pipe joint compound is also designed to resist cracking or becoming brittle. It provides a tight seal, but allows you to disassemble the joint if necessary without damaging the pipe threads. It can be applied in low temperatures and holds in temperatures up to 350 degrees Fahrenheit. Pipe joint compound's main strength is that it is able to hold its seal in pressurized situations, such as with water supply pipes.
Although manufacturers claim that plumbers putty is permanently flexible, it can harden over time and may need reapplication. When applying, plumbers putty must be applied over a thoroughly clean surface. If there are remnants of old putty or dirt present, the seal may fail. Plumbers putty may also contain oil, so it is not ideal for use on natural stone or other porous surfaces. It is not intended for use in pressurized applications, such as water pipes and will not hold its seal if used in these situations.
Pipe joint compound is applied with a brush to pipe threads and can be messy. It is important to purchase the right type of joint compound for the job. For example, pipe joint compound intended for plastic water pipes may not properly seal metal gas pipes and not all pipe joint compound formulations can be used with plastics.