How to Solder Copper Pipe: DIY Pipe Sweating Guide
Nov 15, 2021
When it comes to making watertight connections between plumbing pipes, fittings, and fixtures, plumbers often rely on a method called soldering. This method makes quick, strong, and watertight joints in potable and nonpotable water systems on specific types of pipes.
What is soldering?
Soldering, also known as “sweating,” is a method of joining two pieces of copper together (usually water lines). Using high heat, a plumber joins the pipes with filler metal called solder, which is a flexible metal wire, and a paste called flux, which draws the melted solder into the joint helping to properly seal the connection or joint. Unlike welding, where the two pieces of metal melt together, soldering leaves the copper intact but joins them with melted metal.
When soldering two pipes, the plumber first cleans the fitting and pipe and then applies flux to the inside of the fitting and to the outside of the pipe. Then, using a torch, the plumber heats the joint to around 450 to 500 degrees Fahrenheit (the melting point of the metal solder). Once the joint is hot enough, the plumber then touches the tip of the solder wire to the joint to melt the solder, which allows the flux to pull the solder into the joint. As the joint cools, the solder hardens and creates a watertight seal.
Generally speaking, soldering is used to join pipes that carry drinking water, also known as potable water. For that reason, it’s important to use a lead-free solder specifically labeled for use on copper pipes. Leaded solder does exist (though less common) and is for other uses, such as soldering electronics.
What tools do you need for soldering plumbing pipes?
Soldering plumbing pipes requires a special set of tools:
- Emery cloth is a piece of metal mesh used to clean the end of the pipe before soldering. This helps clean any accumulated dirt and oil, and clean any corrosion from the pipe that may hinder the soldering process and cause pipes to leak.
- Fitting brushes clean the inside of a fitting, and they come in sizes specific to pipe diameters. Similar to the emery cloth, this helps clean the inside of the fittings to better facilitate soldering the pipes together. Be sure you have fitting brushes that are the correct diameter for the pipe you are joining together.
- A pipe cutter features a small cutting wheel and a set of jaws that tighten to cut pipes to length without bending the pipe or leaving burrs behind.
- Pipe reamers can remove any small burrs that do remain, as they can hinder a good seal.
- Acid brushes are soft-bristled brushes with metal handles that the user can dip into the flux to then apply the flux inside the fitting and on the outside of the pipe. These are sometimes called flux brushes or solder brushes.
- A propane torch is a tool you use to heat the pipe and joint beyond the melting point of the solder.
- Lighting a propane torch requires an ignitor of some type, such as a lighter or striker.
- Having a fire extinguisher on hand is important when working with a propane torch, as the possibility of unintentionally igniting a fire is elevated when working with intense flames and high temperatures.
- Position a piece of fire cloth behind the pipe if you’re soldering in tight quarters.
- A spray bottle filled with water is also good to keep around, as you can dampen any wood studs or materials before soldering to prevent burning.
- Heat-resistant gloves to protect your hands and goggles to protect your eyes.
How to solder a copper pipe
1. Cut the pipe to size and ream the burrs
Use the pipe cutter to cut the pipe to length. Ensure that it’s long enough to fit inside the fittings. Use the pipe reamer to remove any burrs from the fresh cut.
2. Clean the pipe and fitting
Corrosion, oxidation, and carbon can prevent a good seal. To avoid this, clean the ends of the pipe well. Wrap the emery cloth around the end of the pipe and hold it in your hand. Twist the end of the pipe back and forth in the cloth until it’s perfectly clean. Clean the fitting by twisting the appropriately sized fitting brush inside the fitting until it’s clean.
3. Apply flux to the fitting and pipe
Using the acid brush, apply flux to the inside of the fitting and around the outside of the pipe. Slide the pipe into the fitting and twist it one-half turn to ensure the flux spreads around the joint. This is also a good time to position the fire cloth behind the joint and dampen anything that can burn with the spray bottle.
4. Prepare the solder
Prepare the solder by unraveling about 8 inches from the spool. Bend the solder downward approximately 2 inches in from the end of the solder wire.