Things You'll Need
120-grit emery cloth
Circular wire brush
Soldering paste and brush
Roll of solder
Water spray bottle
When copper water supply pipes are installed in homes, many of the joints (known as couplings) are installed in vertical, or nearly vertical, positions. As melted solder is used to seal the joint, this means that its lower seam -- where the lower pipe end enters into the coupling -- must receive the solder by its being sucked up vertically into the joint. This process, called capillary action, is carried out by applying soldering paste to the pipe and coupling, which when hot, forces the solder up between the coupling and pipe, creating a water-tight seal.
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Wrap a 6-inch length of 120-grit emery cloth at a perpendicular angle around the outside of one copper pipe end, turning the cloth several times until the pipe underneath becomes shiny. Repeat this process with a second section of copper pipe. Push a circular wire brush inside a copper coupling, and rotate the brush several times.
Brush an ample layer of soldering paste (called flux) around each shiny pipe end, as well as the inside of the coupling. Slip the coupling onto the end of one pipe, and push the other pipe end into the remaining end of the coupling -- position the pipes/coupling in a vertical position in a vise, if practicing installing a vertical copper joint.
Pull a 10-inch section of solder from its roll, and bend the last 2 inches 90 degrees. Turn on a propane torch, and heat around the center of the coupling on all sides. Take the torch away, and listen for the flux to make a sizzling sound. When it sizzles, touch the tip of the solder to the coupling's lower seam. If the coupling/pipe is hot enough for the solder to melt, capillary action will suck the solder up between the coupling and pipe. Apply solder all around the bottom seam. Solder around the coupling's higher seam in the same way. Use a rag to carefully wipe away all solder drips and flux from the joint.
If cutting the pipes to length prior to soldering the joint, use a tubing cutter to cut the pipes as the cut will then be straight and leave no burrs.
Keep a filled water spray bottle close by, in case the propane torch ignites a flammable object close to the soldered joint.