Soldering pipes is one of those things that you might shy away as being too hard to learn, or something only the "pros" know how to do. But with the right tools and just a little bit of practice, it’s a very useful home improvement skill to have.
Get the right tools and supplies
For soldering copper pipe, you’ll first need to pick up a couple of tools, as well as few supplies (in addition to whatever pipe and fittings you need). They’re not expensive, and you can get them wherever plumbing supplies are sold.
The first thing you’ll need is a good torch. The least expensive is a simple propane torch, which is just a nozzle and a valve that attaches to a small, disposable propane cylinder. For a little more money — and it’s worth the investment — you can get one that has a built-in lighter, which means you can skip the matches or the spark striker.
The better torches also work with MAPP gas (a modified propane), which produces a hotter flame. This is something that’s a real advantage when working with larger-diameter pipe and heavier fittings such as valves.
The next thing you’ll need is a tubing cutter. While copper pipe can be cut with a hacksaw, it’s much better to use a tubing cutter. Tubing cutters have a small cutter wheel that comes in contact with the copper as the cutter is rotated around the pipe with increasing pressure, cutting through the pipe and producing a clean, square cut.
To ensure a good solder joint, the pipe and fitting have to be clean. For that, you’ll need a pipe cleaning tool. This is simply a tool with wire brushes in different sizes that cleans both the inside of the fitting and the outer surface of the pipe. You can also use steel wool or emery cloth, but the cleaning tool is faster and easier for the common 1/2- and 3/4-inch pipes used most often.
Finally, you’ll need lead-free solder and acid-free flux or tinning flux, plus a disposable flux brush.
The outside diameter of a copper pipe is slightly smaller in diameter than the inside of the copper fitting. The idea with soldering — also called "sweating a pipe" — is to fill all of that tiny space between the pipe and the fitting with liquid solder. There are three keys to success here: a clean joint, flux and proper temperature.
Cut your pipe to length, and make sure everything is ready to go. Next, clean the end of the pipe and the inside of the fitting with your cleaning brush or other abrasive. Both the pipe and the fittings should look bright, clean and shiny.
Once they’re clean, you next want to apply the flux. Flux helps to further clean the copper, and it also prevents further oxidation during the soldering process and promotes smooth flow of the solder into the joint. Flux comes in a paste form in a small can or jar. It’s applied to the end of the pipe and the inside of the fitting using a small, stiff brush.
Use caution when applying the flux, as it contains chemicals that can be harmful if you get it in your eyes, mouth or open cuts. Read and follow all label instructions carefully! Also, be careful where you set the brush, as the flux is somewhat sticky and it’s easy to pick up dirt and other impurities. If the brush gets dirty, either wipe it clean with a rag, or toss it and use a new one.
Next, assemble the joint by slipping the pipe into the fitting until it bottoms out completely. Rotate the pipe inside the fitting a little to spread the flux. Support the pipe so that the joint stays completely seated during the soldering process. If possible, set up several joints at the same time prior to soldering, so that working on one joint doesn’t disturb the prior joint before it’s had a chance to cool.
However, don’t get too far ahead of yourself. You want to complete the soldering as soon as possible after the joints have been cleaned and fluxed, to prevent the flux from drying out and becoming ineffective.
Now you’re ready to solder. The trick is to heat the fitting, not the solder. The fitting needs to be hot enough to allow the solder to melt and flow, but not so hot that the flux begins to smoke.
Position your torch so that the blue part of the flame is about 1-2 inches from the fitting. Heat the fitting until the flux begins to sizzle, which usually only takes a few seconds. Next, unroll several inches of solder off the roll, and bend about an inch at the end into a 45-degree angle. Now you can test the joint by touching the solder against the seam of the fitting on the side opposite from where the torch is. When the fitting is hot enough, the solder will melt easily. When the whole fitting is properly heated, solder will be sucked very quickly into the joint by way of capillary action.
Needless to say, you’re working with open flame, often in confined areas. Be careful! Always be very aware of where you’re pointing the flame. Keep the torch off until you’re ready to solder, and shut it off between joints. When soldering close to wood and other flammables, use a shield of some sort to avoid igniting the wood. And please be very careful around dryer lint — it’s extremely flammable!