How to Sweat (Solder) Copper Water Pipes for a Watertight Seal

Soldering pipes (called sweating) is the standard way to join two or more pieces of regular copper pipe together.  A solder joint forms a strong, watertight seal that will last for decades or longer when done properly.  In fact, a proper solder joint is less likely to leak than the rest of the copper pipe, which can develop pinhole leaks do to chemical erosion.

For many homeowners the thought of plumbing anything is quite daunting.  We all envision our basements or living areas filling up with water due to some error or oversight in our work.  The truth is that basic plumbing, including sweating pipes as discussed in this article, is a relatively simple job that any motivated homeowner can tackle safely with only a few specialized tools.

This article covers the basics of joining two pipes together.  If you’re looking for more information, we highly recommend Stanley’s Complete Plumbing, which will walk you through this and many other topics in more detail than we can.  Stanley’s Compete Plumbing includes illustrations and detailed steps on an array of plumbing projects, and qualifies for free shipping (purchase over $25) on Amazon.

A note on permits & experience: Some jurisdictions require you to be a licensed plumber to perform plumbing work.  We are DIYers and not licensed plumbers.  This article is for general information.  You may wish to consult with a licensed plumber before undertaking plumbing work in your home or business.  In any event, use this information at your own risk.

Understanding Pipe and Fittings Basics

Most water pipes in a house are between 3/8″ and 3/4″ in diameter.   Main water lines are as large as 1-inch, while small lines (e.g., to a refrigerator icemaker) could be as small as 3/8-inch.  The nominal diameter of a pipe is always 1/8 inch less than the outside diameter.  Copper Pipe wall sizes vary with the size of the pipe such that the inside diameter is always approximately the nominal width.  Copper water pipe is sold in three different wall thicknesses (K, L, M), and can be rigid or soft pipe.  Sizes.com has a great article on copper pipe basics for more information.

In order to join two pieces of copper pipe together, you must use a sleeve (or other fitting, such as the T-joint shown below) which has an inside diameter that matches the outside diameter of the pipe.  In our picture examples below, the T-Joint and valve fit snugly over the copper pipe and are designed to be sweat soldered onto the pipe.  To join two pipes instead of three, you would use a sleeve instead of a T-joint.

Tools and Materials needed to Solder Pipes

The tools and materials list for standard sweat soldering isn’t long or complicated.  We’ve linked to several of the products on Amazon.  Everything is also available in your local big box store or plumbing supply shop.

1. Plumbing Solder (non-lead based).  Solder is sold by the ounce on a spool.  Solder melts at a much lower temperature than copper, which makes it suitable for joining two copper pipes under heat.
2. Copper Pipe Brush.  The brush is used to clean the inside of the fittings and the outside of pipes to prepare them for soldering.  Plumber’s sandcloth can be used as an alternative but this tool makes the job easy.
3. Small Propane Tank & Welding Striker.  Used to heat the pipe and fitting to be joined.
4. Plumber’s Flux.  Used to coat the pipes and fittings to prepare them for soldering.
5. Plumber’s Sandcloth.  Used to de-bur pipes.
6. Heat Resistant Pad.
7. Copper Pipe and Fittings.

Preparing the Plumbing Environment

This tutorial doesn’t cover sweating a joint that is already a part of home’s plumbing.  However, if you were going to work in that environment, these steps are important.  No matter the environment, you should always take precautions to protect the area where you will be heating the pipe with the propane torch.

• Turn off the main water to the house.
• Open the lowest possible valve in the house. (e.g., the utility sink in the basement) to drain all water from the pipes.  Water in the line will prevent the pipe from heating and will cause the installation to fail.  You may also need to open a pipe on the top floor of the house to relieve vacuum pressure.
• Disconnect any PVC plumbing from the nearby copper. (Newer homes may have a combination of PVC and copper piping).
• Protect objects around the joint area from heat.  You will be working with a propane torch that burns at over 1000 degrees.  Be sure there are no combustible materials nearby, and that you put up a heat guard between the torch and any flammable materials, such as wood studs.  An assistant may be appropriate.
• Ensure adequate ventilation in your work area. Open doors and windows and consider running a fan.
• Do as much work as possible at a bench. If you are making several joins, work as many of them out of the plumbing line as possible.

Preparing Copper Pipes for Soldering

• Step 1: Using the copper pipe brush, clean the outside of the pipe and the inside of the fitting. After cleaning, the pipes should be free of debris and appear shiny.

• Step 2: Inspect the pipe and the fitting for burs (small pieces of metal on the fitting or pipe that prevent an easy join).
• Step 3: Try dry fitting the connection to ensure they easily connect.  If they don’t fit easily and snugly, clean the pipes further using the copper pipe brush or sandcloth (shown below).

• Step 4: Once dry fitting is successful, separate the pipe and fitting and apply plumber’s flux to the outside of the pipe and inside of the fitting. During soldering, plumbing flux will evaporate and draw the solder into the joint, forming a tight seal all the way around the joint.

Soldering the Pipes

• Step 1: Light the propane torch and turn the flame to medium.  Note: Most torches will produce more flame when tilted downward.  Be careful to hold the torch in a consistent way.
• Step 2: Point the flame directly at the joint. The joint will heat up after about 20-60 seconds.  (Note that the picture below shows the valve closed.  We’ve gotten some advice below that it would be better for the valve to be open to reduce the risk of damage to the valve).

• Step 3: Touch the solder to the crease between the fitting and the pipe. When the joint is hot enough, the solder will melt and capillary action will pull the solder into the joint.  As the solder starts to melt, move it all the way around the joint.  When solder pools outside the joint, the joint is stable.
• Step 4: Turn off the heat and allow the pipe to cool.

Testing the Solder Joint

1. If you followed these instructions, the joint is likely very tight.  The only good way to test is to put pressure on the joint (turn on the water to the house).  Be sure to wait until the solder has cooled (2-3 minutes) before pressurizing the line to avoid the solder cracking due to a quick change in temperature.

More Plumbing Help

For more information on this and other plumbing topics, we highly recommend Stanley’s Complete Plumbing, which covers this topic in more detail and many other home plumbing scenarios.  Good luck with your plumbing!

What do you think? Tackled any plumbing projects in your own home?  Would you change anything here?

by: Fred | January 13, 2009 | filed in: Projects
Related Tags: plumbing

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