Pipe joint compound, also known as pipe dope, is a type of sealant used with any threaded pipe to help create a seal. Consisting of a mixture of substances, including kaolin clay, vegetable oil, rosin, and ethanol, pipe joint compound serves as both a lubricant and a sealant for threaded joints. Using pipe joint compound on the threads of a pipe joint helps to ensure a water- and air-tight seal. Any plumbing project involving the use of threaded pipe requires the use of a sealant in the form of pipe joint compound, plumber's tape (Teflon tape), or a combination.
Buying Pipe Joint Compound
Pipe joint compound is available in a tube or a canister with a brush applicator. The manufacturer's specifications are an important consideration when purchasing a sealant for your particular project. It is important to note if the product is intended for use on only one certain type of pipe, or if it is a universal product that can be used on both metal and plastic. When buying pipe joint compound, look for a product that can be used on all types of plastic and metal threaded pipe, and keep it on hand as part of your collection of basic plumbing tools and materials.
Some types of sealants are not appropriate for both water and gas. Plumber's tape, for example, comes in two types—one for use specifically on gas and one for water pipes. This can also be true for a pipe joint compound, so read the product usage specifications carefully, and if you are not comfortable sealing gas pipes, contact a professional immediately.
Equipment / Tools
- Compressed air
- Wire brush
- Flat-head screwdriver
- Pipe joint compound
- Plumber's tape (optional)
- Rubbing alcohol
- Clean rags
Clean the Threads
Before applying pipe joint compound and/or tape, clean the threads and remove dirt, oil, and scum. Metal threads can be fragile, so gently use a wire brush or compressed air to clean out the gunk.
For PVC threads, try scraping gunk out with a small flat-head screwdriver and some rubbing alcohol on a rag to cut through any residue. Dry thoroughly.
To use pipe joint compound, apply an even coating onto the end threads of the male pipe (the end that will go into the other pipe), using either the applicator brush or a finger. Do not smear the compound inside the pipes.
Then, thread the pipe into the fitting. Make sure to avoid cross-threading that might damage the threads.
Many plumbers use a thin layer of pipe joint compound on top of plumber's tape for a great seal on almost any threaded joints involving water.
Do not overturn or overly tighten the joints. Tighten joints with a wrench or fingers (depending on the size), and then add one or two more smooth turns. Then resist the urge to turn them "just one more time" or you'll run the risk of damaging the threads or expanding the fitting, which disrupts the seal.
Wipe Away Extra Compound
Use a clean rag to wipe away excess compound from the joints. No drying time is necessary.
When to Call a Professional
If you used pipe joint compound products but there's still a leak or you accidentally cross-threaded the pipes, do not layer on the material to try to stop the problem. Instead, it's best to call in a professional plumber to fix or replace the problem area. In addition, if the threads are too dirty to clean, pipe joint compound will not work, and a professional will need to assess the problem.