How to Solder Copper Repiping Joints

Items Needed:

  • Pipe Cutter
  • Reaming Tool
  • Emery Cloth or Scotch Bright (for prepping soldering areas)
  • Clean, Dry Rag
  • Solder Flux
  • Lead-free (95/5) Solder
  • Propane Torch

If you are familiar with mechanical assemblies, you probably already know that perfection is achieved in the preparation. Soldering copper piping joints is no different in this respect, so make sure you follow the instructions below to get nice clean, and most important, leak-proof solder joints. Prepare your joints properly and you will get a nice watertight seal – don't and you will get a leaky joint.

Solder melts at much lower temperatures than the copper you are working with. If you use solder flux (an acid based, water-soluble paste) liberally and your joints are hot enough, the solder will automatically wick into the joint by way of capillary action, boding with the copper at a molecular level.

Solder a couple of test joints before you start soldering functional pieces together. Although soldering is not difficult, it does take a little finesse to make it look good and get faster at it.

Step 1: Measure and Cut

Measure each of your cuts at least twice to ensure that your measurements are correct. To cut the pipe, tighten pipe cutter and start turning – tightening more as you go, but don't over tighten or you will bend the pipe instead of cutting it. You may have to tighten several times in the course of a single cut. Take it nice and easy to begin with – you'll get faster as you go along when you learn how tight you really need it.

Step 2: Reaming and Cleaning Parts after the Cut

Ream the cut ends to remove any burrs. Clean solder mating surfaces using a piece of emery cloth or Scotch-Brite. You will notice an increase in luster as you remove the oxidized copper from the surface. Wipe off grit with a clean cloth. This will help the solder to wick into the copper itself. Not prepping solder surfaces in this manner results in leaky joints.

Step 3: Assembly

Liberally brush solder-flux to all abraded mating surfaces and assemble the joint. Using the torch, move the flame around so that the joint area is heated evenly. Keep the flame far enough back so that only the tip of the blue flame is in contact with the copper. Too close or too far away and it will take longer to heat the copper.

As the flux melts, the copper will get shiny and the flux will start to bubble, eventually sizzling and smoking. Now is the time to apply the solder. Back the torch flame away so it is not touching the solder directly or you'll make a mess. Touch the solder to the lip of the joint. Keep moving the solder to other areas of the joint to ensure good coverage. You may have to get the joint hot again in the process, but you'll know when to do so; the solder won't be melting against the joint.

For horizontal joints, start at the bottom and move your way to the top and down the other side. Once again, you'll see the solder wick in.

Step 4: Cleaning Excess Solder

Apply some solder flux to the joint while the joint is still warm and wipe off excess solder with a clean rag.