How To Solder a Pipe

Soldering copper pipes creates a watertight seal between pipes and fittings, ensuring leak-free plumbing. While it may seem daunting at first, with the right tools and techniques, you can master this valuable skill. This Old House plumbing and heating expert Richard Trethewey demonstrates the proper techniques for soldering copper pipes in the video above. In this article, we’ll explore the step-by-step process of soldering pipes, alongside expert tips to achieve the best results. 

Understanding Soldering Basics

Soldering, also known as “sweating” pipes, is the process of joining metal surfaces using a filler metal (solder) that melts at a lower temperature than the base metals. For copper pipes, this creates a strong, long-lasting connection that can withstand the pressures of a home plumbing system.

The Science Behind Soldering

When heat is applied to copper pipes and fittings, the metal expands, creating microscopic gaps. As solder is introduced to these heated surfaces, it melts and flows into these gaps through capillary action. Once cooled, the solder solidifies, forming a tight seal between the pipe and fitting.

Types of Solder

There are two main types of solder used in plumbing:

• Lead-free solder: This is the standard for modern plumbing systems, as it’s safe for potable water. It’s typically an alloy of tin and copper.
• 50/50 solder: A mixture of 50% tin and 50% lead, this type is only used for non-potable water systems or heating applications. Always use lead-free solder on your home’s plumbing system.

Deciding to Solder

Even experienced DIYers need to know when they can take on a job themselves and when it’s best to call the professionals. State regulations differ when it comes to which jobs must be performed by licensed plumbers. However, these tasks require permits and should always be left to professionals:

• Pipe installation or replacement
• Plumbing ventilation
• Water heater installation
• Work on gas lines

Minor repairs and leak fixes are safe to do yourself, but you don’t want to make any changes that could compromise your safety or the value of your home. Part of being a good DIYer is knowing when to ask for help.

Gathering the Tools and Materials Needed for Soldering

Before you begin soldering, gather the required tools and materials.

Tools

• Emery cloth or cleaning brush: Cleans the surfaces of the pipes and fittings
• Fire extinguisher: Increases safety in case of an accident
• Flux brush: Applies flux evenly to the pipe and fitting surfaces
• Heat-resistant gloves: Protect your hands from sparks or dripping solder
• Heat shield: Protects surrounding materials from the heat of the torch
• Propane torch: Provides the heat necessary to melt the solder
• Tubing cutter: Ensures clean, straight cuts on the pipe ends
• Reamer or file: Removes burrs from cut pipe
• Safety glasses: Shields your eyes from sparks and splatter

Materials

• Clean cloth: Used to wipe away excess solder
• Copper pipes and fittings: The components you’ll be joining
• Flux: Helps the solder flow and prevents oxidation during heating, also known as soldering paste
• Lead-free solder: The filler metal that will create the seal

Preparing the Pipes for Soldering

Before you light your torch, make sure the pipes you’re working on are clean and fluxed. 

Cleaning the Surfaces

1. If necessary, use a tubing cutter for a clean, straight cut on the pipe ends.
2. Remove any burrs or rough edges from the cut pipe using a reamer or file. Make sure copper shavings don’t fall into the pipe.
3. Clean the outside of the pipe and the inside of the fitting using an emery cloth or a cleaning brush. Remove any fingerprints on the areas to be joined.

Applying Flux

1. Use a flux brush to apply a thin, even layer of flux to the outside of the pipe end.
2. Apply flux to the inside of the fitting as well.
3. Immediately insert the pipe into the fitting, twisting slightly to spread the flux evenly.

The Soldering Process

With the pipes prepared, it’s time to begin the actual soldering process. 

Setting Up Your Torch and Solder

1. Thread the torch tip onto the propane cylinder. Make sure it’s securely attached to prevent leaks.
2. Open the valve and ignite the propane using a striker or built-in igniter. You want a steady and strong flame.
3. Adjust the valve to create a sharp, well-defined pencil-tip flame. This type of flame provides the right amount of heat for soldering copper pipes.
4. Unwind the solder and cut off about as much as you need. Bend the solder at a 90-degree angle to make it easier to hold.

Soldering the Joint

1. Put the heat shield between the joint you’re soldering and any flammable material.
2. Apply heat to one side of the copper fitting. Move the flame around the fitting to evenly heat it.
3. Continue heating until the flux begins to bubble and sizzle. This indicates that the metal is hot enough for soldering.
4. Once the flux is bubbling, press the solder against the opposite side of the fitting from where you’re applying heat. The heat will draw the melted solder into the joint through capillary action. Do not heat the solder itself.
5. Continue applying solder until a small bead appears around the entire joint. This ensures that the joint is completely sealed.

Cooling and Cleaning

1. Remove the heat source once the joint is fully soldered. 
2. Allow the joint to cool naturally for a few minutes.
3. Use a clean, dry cloth to wipe away any excess solder while it’s still warm. This gives the joint a neat appearance.
4. Also wipe away any remaining flux, which can cause discoloration and damage over time.

Tips for Successful Soldering

For the best chance of achieving quality results, keep these expert tips in mind:

• Always work in a well-ventilated area to avoid inhaling fumes.
• Confirm all water is drained from existing pipes before soldering. Water can prevent the joint from reaching the necessary temperature.
• Keep a spray bottle of water nearby to quickly cool joints if needed.
• Practice on scrap pieces of pipe before tackling your actual plumbing project. This helps improve your technique.
• Use a fireproof heat shield to protect surrounding wood framing, insulation, and other combustible or meltable materials. This helps prevent accidental fires.

Troubleshooting Common Soldering Issues

Even experienced plumbers occasionally encounter issues when soldering. Here are some common problems and their solutions.

Leaky Joints

If you discover a leak after soldering:

1. Disassemble the joint and clean all surfaces thoroughly. Check that all oxidation and dirt are removed.
2. Reapply flux and reassemble the joint. Make sure all surfaces are covered with flux.
3. Reheat the joint and apply additional solder as needed. Make sure the solder flows completely around the joint.

Discolored or Burnt Pipes

Overheating can cause pipes to burn or oxidize. To prevent overheating:

• Use the correct flame size for the pipe diameter. A smaller flame is sufficient for smaller pipes.
• Keep the flame moving to distribute heat evenly.
• Remove the heat as soon as the solder flows completely around the joint.

Solder Not Flowing Properly

If the solder isn’t flowing into the joint, it may be due to:

• Insufficient heating: If the joint is not hot enough, the solder won’t melt. Pull the solder away and continue to heat the pipe with the torch.
• Dirty surfaces: Clean the pipe and fitting thoroughly before applying flux.
• Old or contaminated flux: Use fresh flux for proper flow.

Safety Considerations When Soldering

Soldering involves high temperatures and potentially harmful materials. Always prioritize safety by:

• Wearing safety glasses
• Using heat-resistant gloves
• Working in a well-ventilated area
• Keeping a fire extinguisher nearby in case of emergencies
• Allowing joints to cool completely before testing or pressurizing the system

Our Conclusion

Learning how to solder copper pipes will allow you to fix leaks or change fittings yourself. We recommend practicing a few times on a spare pipe until you’ve got the hang of getting the solder to flow where it needs to. Remember to prioritize safety, prepare your surfaces properly, and consult a licensed plumber for substantial changes to your home’s plumbing system.