How to Solder Copper Pipe

1. Prepare Tools and Materials

   Before you can begin soldering, you need to gather the appropriate tools, materials, and safety equipment. Prepare an area where you can work, keeping in mind that it needs to be in close proximity to the plumbing system that you are working on. Place a drop cloth on the ground so that floor is protected from solder, flux paste, and copper shavings.

   Make sure that you have safety glasses, safety gloves, and breathing protection. Solder and solder paste can both produce powerful fumes, especially when you are working in a cramped space, like under a sink or in the basement. Keep the doors and windows open and use a fan to help ventilate the space while you work.

   Warning

   You will need to use a blow torch to solder copper pipe, so it's important to have a fire extinguisher on hand. You should also have a towel and a bucket half-filled with water in case of emergency.
   

   If you are working close to an object or surface, then it's recommended to use a heat shield or fire-retardant cloth to protect the vulnerable material from the flame and heat produced by the torch.
   

2. Turn off and Drain the Water

   The water needs to be turned off and drained before you can solder plumbing lines in the home. You can use an isolation valve to only turn off the water to the area where you are working or, if you don't have an isolation valve, you will need to turn off the main water valve for the entire home.

   Drain the remaining water from the plumbing system by opening nearby faucets, but keep in mind that there will still be some water left in the pipes, so have a bucket prepared when you cut into the existing plumbing.

   It's essential to stop the flow of water to the area where you will be soldering because water in the line will cool the copper and prevent the solder from forming a watertight seal.
   

3. Lay out, Measure, and Cut Copper Pipe

   Lay down the first piece of copper pipe that you will be working on. Use a tape measure to measure the desired length of pipe. Keep in mind that it's always better to cut the pipe too long and have to trim the end than it is to cut it too short and have to use an entirely different piece.

   You can cut through the copper pipe with an adjustable pipe cutter that is suitable for most common residential pipe diameters. You can also use a pipe cutter that is made for a specific pipe diameter as long as it matches the size of material you are working on. If you don't have a pipe cutter, it's recommended to get one, though in emergencies you can also use a hacksaw or a grinder to cut through a copper pipe.

   At this point, it's a good idea to put the various pieces together as you measure and cut the copper to ensure that everything fits according to your project plan. Note that you won't be soldering at this point, just measuring and testing before taking the pieces apart again.
   

4. Clean the Pipe and Fittings

   Cleaning the pipe may sound odd, but the intent is to remove any burrs that could have been made when you were cutting the pipe and to scuff the smooth surface of the pipe so that it's easier for the solder to bond to the copper. Use grit cloth to clean the pipe and scuff the surface of the copper pipe end, slightly farther than the depth that the fitting will reach, until it has a scratched, but shiny, appearance.

   Warning

   Make sure you are wearing safety gloves during this step. The cut edges of a copper pipe can slice through the grit cloth and your skin very easily if pressure is applied at the wrong angle.

   You will also need to prepare the inside of the fittings in the same way, except instead of using grit cloth, you can use a wire fitting brush that slides inside the fitting and scuffs the copper when you rotate the brush.
   

5. Apply Plumbing Flux Paste

   Each step of the soldering process is designed to help improve your likelihood of creating a neat, leak-free joint. Plumbing flux paste is a chemical compound that helps to clean the copper pipe and fittings, but it also works to draw in the liquid solder during the soldering process.

   Use a flux brush to apply the flux paste to the exterior of the copper pipe end and the interior of the copper fitting. Make sure to set the pipe and fittings in a safe place to avoid getting any dirt, hair, or other debris stuck in the flux paste. Debris can prevent the solder from sealing completely, leaving a leak in the soldered joint.
   

6. Assemble the Plumbing

   If you previously assembled the plumbing parts while you were cutting and measuring the copper pipe, then this step should be fairly straightforward. Simply slide the fitting over the end of the copper pipe and repeat with each piece in the plumbing assembly according to your project plan.

   Soldering copper pipe can be as simple as a single joint or far more complex with multiple joints, valves, couplings, and more. Each piece is a part of a larger puzzle, so as long as there aren't any leaks and it all makes sense in the end, the project can be as simple or complex as your skills allow.

   If you didn't take the time to fit the plumbing together while you were measuring and cutting, then you may find that some of your pieces of copper are too long or too short. Trim the pieces that are too long and replace the pieces that are too short. Make sure to clean the pipe again and reapply the plumbing flux paste.

7. Apply Heat and Solder

   Once the copper pipe and fittings have been assembled, position a heat shield or fire-retardant cloth to protect any vulnerable surfaces and pull out about 3 to 4 inches of solder from the roll. The solder can be pulled out and turned into a small hook shape that will make it easier to apply along the entire edge of the fitting.

   Carefully light the blowtorch, adjust the flame so that it has a sharp, blue appearance, then apply the tip of the flame to the underside of the copper fitting. It won't take long for the copper to begin to heat up, so after 15 to 20 seconds, use your other hand to apply the solder to the top of the joint. If it doesn't liquefy on contact, wait a few seconds without removing the flame from the pipe.

   Once the solder begins to liquefy, remove the flame and apply the solder around the joint, filling the entire gap between the copper pipe and fitting to ensure that it forms a complete seal. Repeat this process as necessary with every new joint in the plumbing assembly to solder the entire assembly together.

   Remember, your plumbing assembly may just be two or three pieces, but a more complex project can easily have over 20 pieces to solder together. Do not attempt a complex project until you feel confident in your soldering skills.

   Tip

   While you can use a standard propane torch for soldering, a blow torch equipped with MAPP gas is much more effective because MAPP gas burns at a higher temperature, allowing the copper to heat up quickly and reducing the chance of permanently warping the metal through sustained heating.

8. Clean the Soldered Joints

   The soldered joints should be allowed to cool for several minutes before attempting to clean them. Once it is safe to do so, use the wet towels to wipe the plumbing down and remove any leftover flux paste. If the flux paste is left on the pipe, it can lead to premature degradation due to the corrosive qualities of plumbing flux.
   

   Inspect the soldered joints carefully and re-solder any joints that do not appear to be completely sealed. While a visual inspection isn't a foolproof way to spot leaks, it is easier to fix a mistake now than it is after turning the water back on.

   The reason for this is that when the valve is turned back on, the pipes will fill with water and any leaks will be clear to see, but even after turning the water off again, you will not be able to drain the water without cutting into the plumbing.

9. Test for Leaks
   

   With the job done, all that's left is to make sure that the joints do not leak. Slowly turn on the water and watch the plumbing for any signs of leaks. If you don't spot any leaks, open the valve completely to restore the standard water pressure to the system. Inspect the plumbing again and look for leaking or wet joints.

   If there are any leaks, you will need to shut down the water, drain the line, and attempt to repair the leak. Keep in mind that it's incredibly difficult to solder with water in the plumbing line, so if you cannot drain the water from the area, you may need to cut the pipe and repair this new cut as well as the existing leak.

When to Call a Professional

All but the most experienced DIYers should call a professional for soldering copper pipe. This is a highly advanced project with many risks: Unless you have plenty of experience and all the skills necessary to complete this project safely, hire a professional to complete the work for you.