How To: Solder Copper Pipe Fittings

Connections are made between sections of iron pipe using threaded fittings. The walls of copper pipe, however, are too thin and soft to be threaded, so a different sort of fitting is used, called a sweat fitting. It's called that because the process of joining the various elements using solder involves heating them with a propane torch until they seem to sweat.

There's no particular magic required to solder a sweat fitting, though the very presence of a propane torch makes it a procedure that must be done carefully. Making a tight, leak-free joint is more a matter of careful preparation of the parts than of skill or experience.

Polishing the tubing and fittings. The individual lengths of tubing that link the elements of the plumbing system are connected at fittings. The fittings come in a variety of configurations, including elbows, Ts, forty-fives, couplings, and others. No matter what fitting you are sweating, however, the first step to the process is smoothing and polishing the areas to be joined.

Lay out the arrangement of pipes and fittings, and cut the pipes to length. Make sure the ends are cut square. Use a utility knife to trim off any burrs from the cuts.

At each joint, polish the outside of the pipe using plumber's tape (also called emery cloth, it's sold in narrow strips). Another convenient option for shining pipe surfaces before sweating them is a synthetic, woven abrasive pad. Sold as stripping pads, they resemble those sold for scrubbing pots but will clean and brighten copper in a few easy strokes.

Polish the openings of the fittings, too, using a wire-brush pipe cleaner. Polishing both surfaces is critical: blemishes left on the connecting surfaces are likely to produce leaks later because the solder will not bond properly.

Flux the fittings. Apply plumber's flux to the inside of each fitting to be soldered. Use one of the inexpensive flux brushes made for the task, as it keeps your fingers and hands clean. The flux has the consistency of a thin grease, and when heated will draw the solder into the fitting. Slide the pipe into the fitting, give it a twist to spread the flux evenly, and wipe off any excess flux that squeezes out.