sweating pipes - heating copper pipe joint

Sweating Pipes: Soldering A Copper Pipe Joint Step-by-Step

ByDino Pelle

The cure for sweating pipes that leak at the joint is to take the joint apart and resolder it (also called sweating). I’m going to show you — step-by-step — exactly how to do it the right way.

What Does “Sweating Pipes” Mean?

Sweating a pipe, also called soldering, is the process of heating solder (a metal alloy) to fuse a copper pipe with a fitting. In plumbing, the purpose of sweating pipes is to create a permanent, watertight seal where the pipe connects to (or joins with) another piece of metal.

The joint (or connection) is heated with either propane or MAPP gas. Once heated to the proper temperature, the solder is added to the joint. Once cooled down, a permanent seal is created.

sweating pipes - spool of lead-free solder
This is an example of “solder” which is applied to a heated copper pipe joint (using either a propane or MAPP torch). Today, lead-free solder is often used to prevent any occurrence of toxic lead leaching into the water supply.

How to Sweat Copper Pipes at the Joint

IMPORTANT: Before you begin sweating your pipe joint, make sure you follow safety protocols. Using a propane or MAPP torch is dangerous if mishandled. Wear heavy work gloves and a pair of safety glasses.

Protect any nearby flammable materials by placing a fireproof heat shield between it and the source of any heat. In addition, have a dry-chemical fire extinguisher with you in case the project gets out of hand.

1. Disassemble a Soldered Joint

  • Turn off the water
  • Make sure the pipe is drained of any remaining water.
  • Ignite the propane torch and play the flame over the fitting until the old solder melts.
  • Quickly pull the pipe from the fitting.
  • Do this again to separate the other fitting.

2. Clean the Joint

  • Thoroughly burnish (polish by rubbing) the fitting inside and out with a wire brush or emery cloth, then wipe with a clean cloth.
  • Be careful not to touch the polished surfaces since dirt or grease — including the oil from yoru fingertips — may interfere with the capillary action of the solder. Capillary action as it applies to soldering or sweating pipes is described in the video below.
  • Cleaning the pipe and fitting helps the solder flow evenly to form a watertight joint.

3. Apply Flux

  • Available as a paste or liquid, flux is a material that cleans the copper pipe while helping the solder flow more readily.
  • With an applicator or small brush (this usually comes with your can of flux), apply a light coat of flux to the inside of the fitting.
  • Apply a heavier coat to the outside ends of the pipes.
  • If water drips from either pipe, make a temporary dam using a ball of white bread (sounds odd and funny, but it works). Later, it will dissolve and drain away.
  • Now, push the pipes into the fitting.
sweating pipes - apply lead-free tinning flux
There are a few different types of flux. We suggest that you purchase a lead-free “tinning” flux for a better watertight seal.

4. Solder the Joint

Whether required by code or not, lead-free solder will reduce the risk of toxic lead entering your water supply.

  • Ignite the propane torch and play the inner core of the flame over the fitting, but do not touch the flame to the solder itself.
  • To test if the fitting is hot enough, touch the tip of the solder to the joint. If it melts, apply more solder.
  • The capillary action will pull the solder into the joint to seal the connection (you might not be able to see this happening, but trust me, it’s happening.
  • Apply solder until a bead of metal appears completely around the rim and starts to drip. Any gaps will probably leak, so be thorough (but not excessive) in applying the solder.
  • Repeat to join the other end of the pipe and fitting.
  • Wait a few minutes for the connection to cool.
  • Turn on the water, slowly at first, to test for leaks.
sweating pipes - soldering copper joint
Before soldering your copper pipe, make sure you have prepared the joint by cleaning and fluxing it. And make sure to use lead-free solder.

Final Thoughts

If you’ve followed these instructions, congratulations! You’re now capable of sweating copper pipes.

You probably found that the process is easier in reality than how it seems in the above instructions. I get it. Anytime you break out a propane torch, it can be a little scary. But trust me, once you try this once, soldering copper can be addicting.

So, go for it. Just make sure you follow those safety protocols.

Call 1-Tom-Plumber

Don’t hesitate to contact us here or call us at 1-Tom-Plumber (1-866-758-6237) if you need help sweating pipes or replacing them.

1-Tom-Plumber’s certified team of plumbers and drain technicians respond immediately to any emergency plumbing, drain cleaning, or water damage problem. We also handle the excavation of underground water lines and sewer main lines. Our immediate-response team is available every day and night of the year, even on holidays.

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