Sweating Copper Water Lines

Copper lines fit together with lead-free, solid-core solder. The soldering process involves heating the pipe and is commonly called “sweating.”

Before cutting any “live” water lines, make sure the water supply valve is off. Open the house’s highest and lowest faucets to drain the water lines.

NOTE: Even a small amount of water in a copper line can prevent the joint from heating up enough to accept solder.

Cut the pipe with a hacksaw or a tube cutter by gradually tightening it to score and cut the pipe. Some cutters also have a triangular reamer that can be used to remove burrs.

Sand both the fitting and pipe surfaces to be soldered with a wire brush or emery cloth and wipe clean with a rag. Then apply flux on both pieces. Flux prevents the joint from oxidizing and helps solder flow and bond to the copper.

Fit the pieces together and heat the joint with a propane torch. It should only take up to 30 seconds to get the temperature hot enough to melt solder.

Pull the solder across the heated joint. The solder should virtually suck up in and around the joint. If the joint still doesn’t melt solder, there may be water in the line.

Quickly wipe away any excess solder with a rag and allow the joint to cool and set up.

Once you’re done soldering the run, brace the pipe between joists with brackets/braces to prevent them from banging and stuff insulation in any holes in joists that the pipes go through.

Prevent fasteners from puncturing water lines, nail up protective plates across framing members.