How to Solder Copper Pipes for a Permanent, Watertight Joint

Begin by ensuring your work area is safe. Shut off the main water supply to the house or the branch line you are working on. Open the lowest faucet in the system to drain all water from the pipes. Even a small amount of water will prevent the pipe from reaching the necessary temperature for soldering. Place a heat shield or fire-resistant blanket behind your work area to protect walls and other flammable materials. Keep a fire extinguisher and a bucket of water within arm's reach. Wear safety glasses to protect your eyes from flux spatter and leather gloves to protect your hands from heat.

Measure your copper pipe to the required length. Place the tubing cutter around the pipe at the marked location. Tighten the knob until the cutting wheel just makes contact with the pipe. Rotate the cutter around the pipe, tightening the knob slightly (about a quarter turn) after each full rotation. Continue this process until the wheel cuts completely through the pipe. This method ensures a clean, square cut which is essential for a proper fit inside the fitting.

After cutting, a small ridge or 'burr' will be present on the inside and outside edge of the pipe. This burr must be removed to ensure proper water flow and a snug fit. Use the triangular deburring tool, often attached to the back of the tubing cutter, to ream the inside of the pipe. A few twists will remove the inner burr. Then, use the blade or a file to smooth the outside edge.

This is the most critical step for a successful joint. Any contaminants like dirt or oil will prevent the solder from adhering. Use a strip of emery cloth or fine-grit sandpaper to thoroughly clean the outside of the pipe end that will go into the fitting. Sand it until the copper is bright and shiny, like a new penny, for about 1 inch from the end. Next, use a wire fitting brush to clean the inside of the fitting. Insert the brush and twist it several times until the inside surface is also bright and shiny. Do not touch the cleaned surfaces with your fingers, as oils from your skin can contaminate the joint.

Using a small brush (often supplied in the flux container), apply a thin, even layer of water-soluble soldering flux to the cleaned outside end of the pipe. Then, apply another thin layer to the cleaned inside of the fitting. The flux serves two purposes: it chemically cleans away any remaining oxidation when heated and helps the molten solder flow smoothly into the joint.

Immediately after applying flux, assemble the joint. Push the pipe into the fitting until it bottoms out. Give the pipe a slight twist (about a quarter turn) to ensure the flux is evenly spread. Wipe away any excess flux that squeezes out of the joint with a clean rag.

Unroll about 8-10 inches of solder from its spool and bend the first inch at a 90-degree angle for easier application. Light your propane or MAPP gas torch with a spark lighter. Adjust the flame to have a blue inner cone about 1-2 inches long. Begin heating the joint by applying the tip of the blue inner cone to the middle of the fitting. Do NOT heat the pipe directly. Move the flame around the entire circumference of the fitting to heat it evenly. The flux will begin to bubble and smoke, which is normal. In about 30-60 seconds, the copper will be hot enough to melt solder. You can test the temperature by briefly touching the solder to the joint on the side opposite the flame. If it melts instantly, the joint is ready.

Once the fitting is hot enough, remove the flame and touch the tip of the solder to the point where the pipe meets the fitting. Touch it to the side of the joint opposite where you were just heating. Capillary action will suck the molten solder into the gap between the pipe and fitting. Continue feeding the solder into the joint as you move the solder tip around the seam until a bright, continuous silver ring appears around the entire joint. For a 1/2-inch pipe, you will only need about 1/2-inch of solder. Once the gap is filled, remove the solder.

Allow the joint to cool undisturbed for several minutes. Do not move or stress the joint while the solder is solidifying. Quenching the joint with water can stress the metal and cause a hairline fracture, leading to a leak. Once the joint has air-cooled enough to be safely touched, use a damp rag to wipe away any remaining flux residue from the outside of the pipe and fitting. This is important because flux is acidic and can cause corrosion over time.

After all joints have been soldered and have completely cooled, you can test your work. Ensure all faucets are closed. Slowly turn the main water supply back on. Listen for the sound of rushing water filling the pipes. Once they are full, carefully inspect each solder joint for any drips or leaks. Use a dry paper towel to wipe around each joint; even the smallest leak will show up as a wet spot on the paper. If a leak is found, the water must be shut off, the pipe drained, and the faulty joint must be disassembled, re-cleaned, and re-soldered.