Sweating Copper Pipe in Your Wall

Sweating Copper Pipe

The plumbing supply lines in your walls are probably copper pipe. There are a few other materials they could be, like the newer PEX or the older galvanized steel, but chances are they’re copper. If you have a leak in one of those pipes it has to be fixed right away, and the best way to do that is with solder.

Repairing or installing copper pipe and fittings with solder is called “sweating,” or “soldering” interchangeably, but no one would ever say they sweat electronic connections, so sweating copper is more specific. It’s also not that hard to do.

Your Blowtorch

Yes, you get to use a blowtorch. BernzOmatic has a plumbing torch kit that packages almost everything you need together. You get a tank of propane, a torch head with a trigger starter, lead free flux, lead free solder and a brush for the flux. The only thing I’d add to the kit is a roll of emery cloth for cleaning the pipe. This is like sandpaper, but tougher and you’ll use it to clean the pipe. If you didn’t get this kit, make sure to get lead free solder and flux, suitable for potable water.

BernzOmatic kit

Obviously, a blowtorch is not a toy, so follow the safety instructions and get comfortable and familiar with it before you start in on the task at hand. If there’s a fair amount of light where you’re working, you might not be able to see the flame, but you can hear the difference between the propane flowing out of the nozzle and the fire actually burning. It’s not heavy, but get to know the weight of it and how to move it around to the various angles in which you’ll be using it. Dropping an unfamiliar drill-driver the first time you use it is not the same as dropping a burning blowtorch. That said, following the obvious precautions, this is a useful tool that you should have in your arsenal.

Do have a fire extinguisher close by.

Accessing the Pipe

Leaking pipes are not conveniently located. Ever. They’re inside the walls or under your house. If you’re lucky, the leak is in a place where you can see it, maybe exposed in your basement overhead or behind an access panel. If you’re not lucky (and your plumbing has a leak, so we know you’re not) you’re going to have to hunt it down, cut away some drywall or scuttle into your crawlspace.

cutting drywall

If you’re cutting drywall, make the hole big enough for you to comfortably work in. Cut from stud to stud across and about a foot above and below the leak. The best tool for this is a keyhole saw. It has a sharp toothed, pointed blade, and it’s also called a “jab saw” because you can easily smack it on the butt with the palm of your hand and jab it through the wall. Watch the video and you’ll see I couldn’t find my keyhole saw, so I used a cheap, folding saw that I think came free with another tool. The blade is too flexible to effectively jab it through to start, but you can see it still works. You can also use a spent sawzall blade and they sell handles just for this purpose.

If you’re going to be deep under your house in a narrow crawlspace, lying on your back, unless you’re already good at this, call a pro.

Cutting the Pipe

You’ve found the pipe and identified the leak. If you haven’t done it already, turn off the water. There might be a valve that shuts of the section of pipe in question, but if there isn’t then shut off the water to the whole house. You should already know where this valve is. Open the taps after the water’s off to drain the water from the pipe. You can’t sweat a pipe with water in it.

With the water off and the pipe drained, mark a location on either side of the leak where you’ll cut the offending section away. An inch or so on either side gives you room to work. Now wrap a strip of emery cloth around the cut point and work it back and forth like a burlesque dancer with a scarf between her thighs until the copper is shinny all the way around. Do this at each cut point. You want the copper to be clean and it’s easier to do this before it’s cut.

emery cloth

Secure your pipe cutter around the pipe and tighten it down with the thumbscrew. Twist it around and around, tightening it every few turns. It might take a couple minutes, but the sharp cutting wheel bites into the copper, scoring a straight line all the way around and making a very clean cut. Some water will drain from the pipe. Catch it with a rag.

pipe cutter

Making the Repair Piece

Cut a replacement piece of pipe the length of the distance between the two cut ends. If it’s a straight section all you need is a section of pipe and 2 straight connectors, all of the same diameter as the old pipe. If it’s got an elbow, then you need the elbow fitting, 2 pieces of pipe and 2 straight connectors. Clean out the insides of the new fittings and the outside of the replacement piece of pipe with the emery cloth.

replacement piece

Fitting the New Section

Now we’re getting to the meat of the matter. With the brush from the kit spread a thin layer of flux on the outside of the pipe sections and the insides of the fittings. Too much flux can make a mess, but it’s better than too little, which will not work. If it’s ½-inch pipe, you need to flux ½-inch from the end of the pipe, all the way around. Slide the fitting’s over the ends of the replacement piece of pipe and then fit that unit between the cut ends. There’s some flex in the installed pipe, so you’ll be able to manipulate it to make the replacement fit.

Sweating the Pipe

With the new section now in place unroll a length of solder from the spool. For ½-inch pipe, you’ll use ½-inch of solder per joint, and so on for other dimensions of pipe, so unroll enough that you won’t have to worry about feeding it out as you work. Bend the end into a hook, so you can reach around the backside of the pipe.


Safety – When you get your supplies, get a flame proof pad that fits between the pipe and the structure behind it. They’re in the plumbing section. If you overshoot with the torch the pad will protect the wall or framing.

Fire up the torch. If the new section is less than 2 inches long, hold the torch in the middle, moving it a bit so you don’t create a single hotspot. If it’s longer than that, hold the torch in the middle of the lowest fitting and do them one at a time starting from there. Watch the flux. When it starts to bubble, touch the solder to the joint. It should liquefy instantly. If it doesn’t it’s not hot enough. As the solder melts, the flux sucks it into the fitting. Move the solder around the joint to be sure you get it all the way around. Do this at each joint.


Don’t over heat it. Once the flux is bubbling, ease off with the torch or take it away all together. The residual heat will do the work for you. When each joint is done, turn off your torch. That’s it for that.

Cleaning Up

First, do nothing. Do not clean up the newly sweated joints with a damp gag – do not attempt to cool them down – do not turn the water back on. Allow the repair to cool naturally. It won’t take long. When the pipe is back to room temperature, now you can clean it with a damp rag. It might still look a little messy, but that’s okay. What you don’t want is extra flux left behind on the surface.

Turn the water back on and watch your repair. Make sure there are no leaks. If you messed up, it will show right away.

If you had to cut drywall away, consider leaving it open. Unless it’s in a spot where it will be unsightly, it would be good to have access in case of problems in the future. There are access panel doors that fit right into a rough hole in drywall. You can also hang a picture over the hole. If you do need to repair it, We’ll cover that in a future article.



Watch it all happen in the video here: http://doitwithjustin.com/2015/06/23/sweating-copper-pipe-inside-your-wall/

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