Shared Knowledge


How to - Solder Copper Pipes


28 December 2005




Summary: copper joints must be clean, free of any moisture, roughed up and coated with flux before applying heat. Apply heat to the larger diameter of the 2 pipes being soldered.




Not shy about tackling just about any home repair, I have from time to time had to solder copper water or heat pipes. Soldering copper pipe is not difficult but there are several things to keep in mind:


- Use a pipe cutter to cut copper pipe as opposed to a hack saw. A pipe cutter will make a clean vertical cut whereas making a vertical cut using a hacksaw will be difficult and a hacksaw will leave edge burrs, which you will have to remove before you can use the pipe. A pipe cutter for all but the largest diameter cooper pipe is not an expensive investment. When you cut the copper pipe, make sure you allow enough pipe length to fully insert pipe into the fitting you are joining to. A pipe only partially seated into a fitting and then soldered, is not going to hold. The pipe must be inserted all the way into the fitting until it butts up against the fitting flange.


-  Use sandpaper to rough up the surface of the pipe, which is going to be inserted into the fitting at least to the depth of the fitting. Also rough up the inside of the fitting.


- Make sure all copper is free of water, moisture and dirt.


- Get good copper pipe flux and use a flux brush to coat the inside of the fitting and also the entire end of the copper pipe to the length of the fitting depth. (You can buy copper pipe soldering kits at any hardware store, which includes flux, brush, solder and perhaps even a torch.)


- Slowly insert the pipe into the fitting up to the depth of the fitting. Using a propane torch, begin heating the copper fitting (not the pipe), moving the torch flame slowly back and forth. (I suppose the distance you hold the torch from the fitting depends on the torch used but I find holding my propane torch about 2 inches from the fitting is a good distance.) If you are soldering a water pipe, use lead-free solder and place the end of your solder coil on the pipe inserted into the fitting right at the junction of the 2 pieces of copper. When the junction becomes hot enough, the flux will melt and so too the solder and the flux will pull the solder into fitting and around the inserted pipe. Continue to melt solder until you have a nice solder seam around where the pipe enters the fitting. You want a nice seam of solder here so keep applying solder until it literally drips off the pipe.

-  If you have some solder drips or the seam around the pipe fitting is not perfect looking, it really does not matter. However, the solder seam around the pipe and the fitting should appear to be solid all the way around.

-  Allow the pipe and fitting to cool and then turn on the water and check junction for leaks or weeps (a weep is not a drip but junction is moist to the touch). If the junction is weeping moisture, then your solder junction is not sealed. Do not confuse excess flux as moisture. If your junction leaks or weeps, turn off the water, drain the pipe of water, apply torch heat to the fitting and using vice grips or other hand protection, pull the pipe out of the fitting, rough surfaces again, remove all moisture and repeat process defined above.


If you are working in a very confined area, be careful your torch does not ignite materials close to the pipe junction you are soldering. Also be careful handling the torch. Know it sounds ridiculous to warn about this, but when one's focus is on the junction, perhaps in an awkward physical position, it really is not that hard to burn your self or your clothes with the torch. Be careful.


Finally, be aware that it can be almost impossible to re-solder a broken seam on a water pipe. Although you may think you have drained all the water from the associated water pipe, water will still be in the pipe and no amount of heating is going to allow you to get a good new, solder flow to start around the broken junction. Although I am not happy about saying it, but it is better in these circumstances to cut out the bad junction and use virgin pipe. Virgin pipe solders easily, pipes with water in them or where you can not get flux into the junction, will simply never solder well again.