Knowing how to solder a copper pipe, or “sweating” them as some plumbers call it, is key for proper sealing. Most homes use these pipes to distribute water from the main line to sinks, showers, dishwashers, or even to reroute a plumbing vent—and a tiny leak can cause thousands of dollars in damages if it's not fixed right away. You don't necessarily have to hire a plumber to solder copper pipes. Follow the steps in this DIY guide to learn how to solder copper pipes on your own.
What Is Soldering?
Soldering is the process of joining two pieces of metal together by heating solder, which is a metal alloy that consists of tin and lead. While a soldering iron is used for smaller soldering jobs, such as electronics, you typically use a blow torch to solder copper pipe in a process the pros refer to as “sweating the pipes.” When soldering copper pipes, you use the blowtorch to heat the solder to 600 degrees, causing it to melt around the joint between the two pipes. When it cools, it creates a strong watertight joint between the two pieces of metal.
How to Prepare to Solder Copper Piping
Gather together the supplies you'll need for sweating copper pipes. It might be worth having a little extra copper on hand in case you need to cut a longer piece of pipe than initially expected. Always wear gloves and protective goggles when soldering copper pipes and have access to a fire extinguisher for safety reasons.
Keep in mind solder is only meant for metals like copper, brass, aluminum, and steel. This might be a factor if you're trying to decide between copper and PEX piping.
Cut Your Pipe to the Desired Length
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Measure the length of copper pipe you'll need for the finished project, then cut it using a tube cutter to get the right size. Tubing cutters come in small, medium, and large sizes, and some are adjustable to meet the diameter of your pipe. Read the instructions when using a tube cutter. You may need to slowly turn it to make a cut that won't bend the copper—If it bends, it may be unusable.
Deburr and Clean the Pipes
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Before soldering copper pipes, always deburr them first. In other words, remove any sharp edges from the ends of the pipe. You can use a file, sandpaper, or a deburring tool to file down the interior and exterior surfaces of the pipe's edge.
Without taking this step, you risk not creating a tight seal and possibly cutting yourself on sharp edges as you work. After deburring, use a compressed air canister to clear away any excess shavings. You’ll also want to clean the pipe fittings to help ensure a tight seal.
Cleaning your copper pipes is also important for DIY fixing a pinhole leak, which could save you a call to your plumber.
Add Flux to the Pipe and Fitting
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Apply flux to the joint you're soldering using a pipe brush, as well as the pipe fitting. Flux is a compound that goes on the inside of a pipe before heating it to help create an inseparable bond.
Apply Heat to Sweat the Pipe
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Before applying heat, unwind your solder wire. You'll need it in the next step, and it's safer to unwind it now before the pipe gets hot.
Wearing heat-resistant gloves, use your propane torch to evenly heat the pipe and fitting, holding the pipe on the opposite side and rotating it on all sides.
Touch the Solder to the Pipe
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Touch your solder wire to the edge of your pipe and rotate the pipe to coat the entire circumference. If the solder doesn't melt, you need to heat your pipe longer or possibly more evenly around the edges.
Apply Enough Solder Around the Joint
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You may need to add solder several times to coat the whole area. This may require you to do it piece by piece, reheating the pipe as it cools each time. Tackle one joint at a time if you're doing multiple pieces of copper pipe. For reference, you'll need around 1/2 inch of solder for every 1/2 inch of pipe.
Clean Away the Remaining Flux
Clear the remaining flux off with a rag. Excess flux on the exterior can discolor your pipes and wear them out over time. Fortunately, now's the best time to do it since the pipe is hot and it's easy to remove.
Two Tips to Join a Pipe Without Heat
If you don’t feel comfortable wielding a torch to solder two copper pipes together, consider using these two flame-free alternatives instead.
Copper Bonding
Copper bonding is basically glue for copper pipes. It won’t create bonds as strong as soldering, but it requires no expertise, costs less than press fittings, and doesn’t involve a torch or applying heat of any kind:
Prep the pipe as you would for soldering by cleaning and deburring it.
Apply a line of glue around the end of the copper pipe.
Insert the pipe into the fitting.
Rotate the pipe a full 360 degrees to spread the glue around the entire bond.
Allow the glue to dry per the manufacturer’s instructions before putting the pipe back in use.
Press Fittings
This relatively new way of joining copper pipe uses brute force as opposed to molten metal to bond the two pipes. Press fittings don’t require a blow torch, create connections much more quickly than soldering, and require less skill. This makes press fittings similar in many ways to working with PEX plumbing.
Though easier to execute, press fittings do require a larger investment than soldering. The press tool required to make this kind of connection costs $150 or more, and the press fit fittings are more expensive than standard copper fittings.
Prepare the pipe for connecting by cleaning and deburring it. Don’t skip this step as the sharp metal burr can damage the rubber ring in the press fitting that makes the connection watertight.
Insert the press fitting over the copper pipe all the way to the stop.
Use a marker to mark where the fitting ends.
Remove the pipe and measure from the end of it to your mark. Make sure the measurement matches the depth of the fitting.
Reinsert the pipe into the fitting and use the press tool to compress the two metals together to create a tight connection (make sure the fitting doesn’t deviate from the mark you made as you do this).
DIY Copper Pipe Soldering vs. Hiring a Pro
Learning how to solder a copper pipe can save you the cost of a burst pipe repair or allow you to DIY renovations to your home’s plumbing by giving you the skills to connect copper pipes yourself.
However, if you don't have access to the proper materials to solder a copper pipe, such as gloves or a fire extinguisher, it's probably best to hire a local plumber with experience to tackle the job.
Hiring a plumber is also a good idea if you're uncomfortable using a torch. Additionally, excess flux on the inside of the pipes can leave behind an acidic residue, which isn't great for the water flowing through it later.
Flex is necessary for soldering copper pipe. This acidic paste attracts the solder, pulling it deeper into the joint so the solder fills all the gaps between the two metal fittings. While many solder products contain small amounts of flux, you need to apply the additional flux paste to ensure you achieve a water-tight fit between the two copper pipes.
You can use normal solder, which consists of a tin and copper alloy, on copper pipes. You should avoid using leaded solder, especially if you're soldering together water supply lines, as it will contaminate drinking water. One way to test if your copper pipes contain lead is to scrape off the solder. If the scraped area is shiny, it likely contains lead.
Wearing a mask while soldering is a good idea, but if you're in a well-ventilated area or outside, you don't need to cover your mouth. However, you definitely need to protect your eyes from sparks or other debris. You're working with a blow torch here, so taking proper precautions is essential for your safety.
Be careful not to overheat the joint, as this can burn out the paste flux and cause a leak where the solder has not properly taken to the joint. You will know when this happens, as the solder will ball up on the inside of the pipe rather than being drawn into the joint.
A professional content writer, C.E. has written about all things home, family, and wellness for a variety of publications, including HomeLight, Noodle, and Mimi. A third-generation Los Angeleno, she is always looking for ways to make the most of the sun, whether it be building an urban garden or decorating with the help of some low-maintenance, air-purifying plants.
A professional content writer, C.E. has written about all things home, family, and wellness for a variety of publications, including HomeLight, Noodle, and Mimi. A third-generation Los Angeleno, she is always looking for ways to make the most of the sun, whether it be building an urban garden or decorating with the help of some low-maintenance, air-purifying plants.
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