Soldering copper pipes can be tricky, even for experienced plumbers. Errors can lead to leaks, costly repairs, and safety hazards.
The process of joining copper pipe and fittings is called soldering (or sweating), a critical step in the copper installation process. Solder is a metal or metallic alloy that historically consisted of lead (known as lead-based solder) and tin in various proportions. Today, due to the Safe Water Drinking Act and lead-free restrictions, solders that contain more than 0.2% lead are not permitted for use in potable water systems.
Solders that are safe to use on potable water systems contain a percentage of tin and a combination of other nontoxic metals. The melting point of solder is lower than that of copper, and when heated, the solder melts and fuses the piping together once it has completely cooled.
If you're looking to master the art of soldering copper pipes, you’ve come to the right place. In this guide, we'll walk you through common soldering mistakes, how to avoid them, and tips to achieve a flawless soldered joint. Plus, we’ll provide links to valuable resources and products from Oatey to help you along the way.
1. Choosing the Wrong Products
Selecting the correct type of copper pipe, flux, and solder is crucial for a successful soldering job. Various types of copper pipes and fluxes are suited to different applications.
Below, we’ve included some brief guidelines to keep in mind for your next soldering project.
Copper Pipe
- Type K: Has the thickest wall and most robust durability. It is commonly used for commercial plumbing, such as underground water mains for potable water supply and HVAC lines.
- Type L: Wall thickness falls between Type K and M. Typically used for interior hot and cold-water distribution.
- Type M: This type has the thinnest wall and is the most popular choice for domestic plumbing systems due to its lightweight, decreased rigidity, and affordability.
- Copper DWV: Commonly used in older homes for vents and drains. It is no longer a popular choice among modern-day homeowners, as more cost-effective options are available.
Flux
Flux is formulated to remove any oxidation from the pipe and actually etches the pipe surface in preparation for the soldering process to be successful. Important variables, such as ambient temperature, local code guidelines, and any job site time limitations, should all be considered prior to purchasing your soldering supplies.
- Petroleum-based flux (or Petrolatum Flux): Oatey® No. 5 Paste Flux requires flushing and is designed to provide superior wetting properties for better solder flow. It can be used with most soft solders, is 100% lead-free, and is safe for use in potable water applications. No. 5 Paste Flux’s formula prevents copper piping from turning green and is excellent for large-diameter copper pipe applications.
- Hot weather flux: Oatey® No. 5 Hot Weather Flux is specially formulated for hot weather climates and will not separate in temperatures up to 135°F. It cleans and fluxes most commonly soldered metals, including copper, brass, zinc, galvanized iron, lead and tin or copper-coated metals.
- Water-soluble flux: Oatey® H-20®5 Paste Flux is a water-flushable soldering paste flux designed to clean and flux most commonly soldered metals. It is 100% lead-free, safe for use in potable water applications, and can be used on copper piping without discoloration. It is excellent for large-diameter copper pipe applications.
- Tinning flux: Available in both water-soluble and petroleum-based formulas, tinning flux is enhanced with tinning powder particles to pre-tin piping. This improves the flow of solder and enables even heating of a fitting, which is necessary when soldering larger diameter piping systems. Innint flux is compatible with all common plumbing solder alloys. Check out this article to learn how to expertly solder low-lead brass using tinning flux.
Although petroleum-based fluxes are safe to use, they must be flushed with a chemical solution from the piping system due to their water insolubility. However, water-soluble fluxes become self-cleaning and flush away once water enters the system. Refer to manufacturer instructions for product-specific application and safety guidelines to ensure proper use.
Solder
- Tin-antimony solder: Oatey® 95/5 Lead-Free Plumbing Wire Solder contains 95% tin and 5% antimony, is lead-free and is safe for water supply lines. It is designed for use in plumbing applications where frequent extreme temperature changes and vibrations occur (refrigeration, cooling equipment, and heat ducts) and can also be used to solder electronics. The melting range is 450°F to 464°F, and it has an unlimited shelf life.
- Tin-copper solder: Oatey® 97/3 Lead-Free Plumbing Wire Solder contains 97% tin and 3% copper and is lead-free and safe for water supply lines. Designed for sweating copper and brass plumbing joints, it has a melting range of 440°F to 572°F and an unlimited shelf life.
- Silver-bearing solder: Oatey® Silver Lead-Free Plumbing Wire Solder contains silver, copper, bismuth, and tin. Lead-free and safe for water supply lines, this solder is ideal for low-lead brass applications. Its wide melting range (420°F to 460°F) enables more time for soldering joints.
2. Skipping the Prep
Proper preparation is arguably the most critical step in soldering. Oxidation and impurities on the pipe surface can prevent the solder from correctly bonding the pipe and fitting. Neglecting the following three steps can lead to weak joints and potential leaks.
Steps to Prep Copper Pipes:
- Deburr: Use a deburring tool to remove any roughness inside the pipe. This ensures smooth water flow.
- Clean: Remove oils and dirt using an abrasive cloth like Oatey® Plumber’s Abrasive Sandcloth, Oatey® 180 Open Mesh Cloth, Oatey® Nylon Grit Pads or the Oatey® O.D. Tube Cleaning Brush.
- Polish fittings: Clean the interior of the fitting hub with an Oatey® Heavy Duty Fitting Brush.
3. Not Protecting Surrounding Areas
When soldering, especially in older homes, protecting the surroundings from potential fire hazards is essential. Proper protection prevents accidents and ensures safety.
Protective Measures:
- Flame protector: Use a flame-retardant cloth like the Oatey® Flame Protector to shield nearby areas. The Oatey Flame Protector is a non-asbestos flame-retardant cloth that protects studs, walls, floors and other surfaces from flames and sparks when soldering. Made of oxidized polyacrylonitrile (OPAN) fibers, this cloth offers up to 2,280°F of heat protection and is ideal for use with higher-temperature torches, including propane and MAPP gas. Brass eyelets allow for easy hanging from a stud or wall.
- Scrap metal: Place between the joint and any flammable materials.
4. Applying Too Much or Not Enough Flux
It’s tempting to use a large amount of flux, thinking it will improve the soldering process. However, too much flux can lead to severe problems.
Risks of Excess Flux:
- Corrosion: Excess flux turns into acid when heated, traveling inside the pipe and causing pitting.
- Wasted product: Using more flux than necessary leads to unnecessary waste.
We recommend evenly applying a thin layer of this product with an Oatey® Acid Brush to the copper pipe and the inside of a fitting. Any excess flux should be removed prior to connecting them.
While too much flux is harmful, too little can pose issues.
Importance of Sufficient Flux:
- Flow issues: Insufficient flux can prevent proper solder flow.
- Leak paths: Gaps in flux application can lead to leak paths.
Apply a consistently thin layer to ensure optimal results.
For more tips on applying flux, see our soldering tips and techniques.
5. Overheating the Joint
Applying too much heat can cause the solder to drip away from the joint, resulting in leaks. The flame should be removed as soon as the solder melts. Be sure to heat the joint evenly and position the flame at a 45-degree angle near the bottom of the fitting hub. Use the appropriate torch tip size for the pipe. A large tip provides excess heat and risks overheating smaller pipes.
Understanding Heat Requirements:
- Smaller pipes: Require less heat; use a smaller torch tip.
- Larger pipes: Need more heat; use a larger torch tip for even heating.
Follow manufacturer guidelines for best results.
6. Neglecting Cleanup
While the joint is still warm, immediately wipe away any leftover flux or solder drips with a dry rag to ensure copper pipe longevity. Excess flux may seem harmless; however, it can cause Verdigris, a greenish-blue discoloration commonly found on copper, bronze and brass, to form and destroy copper pipe over time. An old, rusting penny and the Statue of Liberty are great examples of Verdigris in action.
