Soldering, also known as sweating, is a foundational skill in plumbing that opens the door to professional-quality copper piping repairs and installations. Heat is applied to a joint between two metal parts—typically copper pipes and fittings—allowing the filler metal to flow into the joint and creating a watertight seal.
Solder is an alloy of different metals, varying depending on the application. Traditionally, solder was made from lead; however, lead solders are no longer used for such applications due to the adverse effects of lead in potable water systems. Despite this, lead solder is still preferred in some areas.
Soldered joints are compact, cost-effective, and ideal for tight spaces, providing a reliable, permanent connection without the need for expensive tools. While alternative technologies like push-to-connect fittings and press systems are popular, soldering offers greater control and durability when done properly.
This comprehensive project guide walks through the complete process of soldering copper pipes, including tools, prep, safety tips, solder choice and mistakes to avoid.
New to soldering? Read: Soldering 101 - Soldering Tools, Tips & Techniques
First, measure the copper pipe to the desired length and cut using a tube cutter. Make sure the pipe is cut square.
Position the cutter around the tube, ensuring the cutting wheel is aligned with your mark. Hand-tighten the cutter gently, avoiding going too tight initially, to prevent flaring or burrs.
Once it’s snug, give it a slight quarter turn. Begin rotating the cutter around the tube, making one or two full rotations before tightening another quarter turn. Repeat this process until the cutter fully penetrates the tube.
After cutting:
Pro Tip: Choose a cutter sized appropriately for your pipe. Large cutters on small-diameter pipe can cause tracking or misalignment.
Clean the pipe's exterior with sand cloth or abrasive mesh. For the fitting interior, use a fitting brush of matching size.
Remember, regardless of the numerous products available for pipe cleaning, they all serve a similar purpose: to abrade and prepare the surfaces. Whether using emery pads, sand cloth, or specialized tools, the key is personal preference and finding the best method for you.
Flux plays a critical role in making a clean, leak-free solder joint by acting as a wetting agent. It helps solder flow evenly into the joint while preventing oxidation as the metal heats up. Without it, the solder won’t bond properly. However, when it comes to application, more is not better.
Pro Tip: Even seasoned plumbers use tinning flux—it’s versatile, forgiving, and ideal for larger pipe sizes or tricky jobs.
Torch tips come in different sizes for a reason. Use a smaller tip for pipes 1 inch and under, and switch to a medium or large tip for bigger diameters.
A larger tip delivers more heat across a wider area, which is critical for larger pipe sizes. An oversized tip on a small pipe can overheat the joint and burn off the flux, causing the solder to fail.
Once the joint is hot enough, touch the solder to the opposite side of the flame. If everything’s properly prepped, the solder should melt on contact and be drawn into the joint by capillary action. Then rotate and apply solder to the other side.
A general rule of thumb is that you only need a length of solder equal to the diameter of the pipe:
More than that is typically waste—it drips, scorches, or ends up on the floor. Excess solder won’t improve the seal and could indicate an underlying issue with cleaning or flux application.
Watch for proper flow:
If the solder flows cleanly and fills the joint, it will “disappear” into the fitting and not run off. If it melts and drops straight down, the joint likely wasn't cleaned or fluxed correctly, or the temperature is uneven.
Pro Tip: Always shield nearby surfaces or components with a flame protector. In confined areas, pre-dampen nearby wood or insulation. Take 20 seconds to visualize your work area. Think to yourself, “If I put the flame this way, am I risking any nearby surfaces?” This will help you avoid accidents and burns.
After soldering, the joint will still be hot—this is your window to finish the job cleanly and safely.
Pro Tip: Keep a rag bucket nearby while soldering. This simple habit pays off in both safety and presentation.
Let the joint fully cool before testing.
Pro Tip: Air testing lets you fix a bad joint by reheating and applying more flux and solder, which is not always possible after water has flowed through.
Working with an open flame means taking safety seriously, especially in older homes or tight spaces. One quick mistake can cause burns or even a fire. Follow these best practices to keep your workspace safe and your joints clean.
Pro Tip: In older homes or tight spaces, spray surrounding wood, joists, or insulation with water before applying heat. Even materials you can’t see can ignite from residual heat or smolder long after you leave the job site.
Selecting the right solder depends entirely on your application. For any potable water application, choose a lead-free option like Oatey® Safe-Flo® or Oatey® 95/5. For larger pipes or thicker joints, Oatey® 97/3 offers a higher melting range and better flow for gap-filling.
Use rosin core solder like Oatey® Rosin Core Wire Solder for electrical work and acid core solder like Oatey® Acid Core Wire Solder for galvanized metal repairs—both feature built-in flux for easier use. Leaded solder may be allowed for HVAC systems, but always check local codes before proceeding.
This guide breaks down the different types of solder, their compositions, applications, and how to pick the right one.
Read this troubleshooting guide explaining how to avoid these mistakes for a clean, leak-free joint.
Working on a more advanced project?
Looking for the right tools and materials? Explore Oatey’s line of trusted soldering products:
They’re the same process—“sweating” is a trade term for soldering.
Most solder melts between 360°F and 460°F. Aim for 500°F pipe surface temperature. Use the correct torch tip and gas (MAPP, propane, or acetylene).
Always use lead-free solder, such as Oatey® Safe-Flo®.
Not directly. You must cut out the joint, clean both surfaces, and re-solder. However, air testing allows you to fix a bad joint by reheating and applying more flux and solder, which is not always possible after water has flowed through.
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