How to solder copper pipe – step by step instructions for sweating copper pipe

Your browser does not support HTML5 video.

Soldering copper pipe, or, sweating copper pipe, as the tradesmen say, uses capillary action to create a tight solder joint. By using a propane torch to heat the two pieces you are connecting, silver solder is “sucked” into the connection and spreads evenly within the copper pipe and copper fitting and covers the mating surfaces completely with molten solder. Once the assembly cools, you should have a solid, leak-free connection that will survive the test of time.

Use care when working with propane torches. Keep the heat away from wood  or other combustible materials. Please let your work cool before touching it.

Tip – Outside sweating of copper pipes will keep the stink outside the house and keep the wife happy … don’t create an unpleasant hobby for the family, don’t  you agree ?

Step 1: Plan ahead

Gather all the items you will need to complete the project. Be sure you have adequate copper tubing and fittings to complete all your angles & runs. You do not want to run to the store in the middle of soldering.

Step 2: Cutting Copper Pipe

Cutting Copper PipeOnce ready, cut all your copper pipe and pieces in to the right lengths. (Don’t forget to add the length of copper pipe that will insert into every copper fitting.) A copper tubing cutter will give you the best cut, however you can use a saw and a chop box if you are desperate. However you cut the copper pipe, be sure to not bend the copper pipe or create cuts in the copper faces that will be soldered. The imperfections can cause leaks. Really, the tubing cutter will give you superior results and finish….and is faster.

A tubing cutter rotates around the pipe as you cut. Move the blade of the tubing cutter to your length mark. Lightly tighten the clamp. Spin the cutter around the pipe several times to lightly score the pipe, then, tighten the clamp a quarter turn after each full rotation. Repeat, and keep rotating and clamping until the pipe is cut, go slowly and take your time….. After a while you will learn to slowly tighten the tubing cutter as you rotate it around the pipe and then the cutting will go pretty fast. It takes 8-10 rotations to cut most pipe.

Tip– tightening the tubing cutter too fast can cause the pipe to bend into an oval shape which will prevent a successful sweating of the joint.

Step 3: Reaming Copper Pipe

Reaming Copper PipeOperate the reaming tool of the pipe cutter,  use in order to remove the burr from the inside of the copper pipe.

Step 4: Polishing Copper Pipe

Polishing Copper PipeNow, prepare the copper pipe and copper fitting to be soldered. Use emery(way better!) cloth or sandpaper and polish the ends of the copper pipe pieces where they will be joined. I prefer the open mesh emery cloth, it lasts much longer and polishes better….continue to polish the copper until the all the metal is shiny. This removes any impurities, dirt, and oxidation that may oppose a leak-free joint. Also, sand the end of the pipe. Do not touch the cleaned copper with bare hands or dirty gloves. Skin oils, dirt, and impurities will impair the soldering operation.

Tip – most water leaks, are from compromised copper, not being properly cleaned, sanded, and prepped.

Tip – Do not use copper polish to clean the copper, it will pollute the metal and prevent you from soldering.

Step 5: Polishing Copper Fittings

Polishing Copper FittingsRotate a wire brush inside the fitting, several complete rotations, in order to polish the insides of the copper  fittings.

Tip – you can cut the handle off the brush, insert the remaining wire into a drill, and quickly sand the inside of the fitting, its easy and fun!

Step 6: Apply silver tinning flux to both copper parts

Apply silver tinning flux to both copper partsBefore you start sweating copper pipes, assemble all the parts, to ensure, that everything fits correctly. Make sure all copper joints slide together without a lot of forceful twisting. If copper pipes, do not slide easily into the copper fittings, ensure they are not bent into an oval shape. Toss and recut copper pipes, if they don’t fit well.

Now, take apart the assembly, and use the flux applicator brush to put a thin layer of flux, on all surfaces, that will be sweated. Flux the outside ends of all the copper pipes, and, the inside of the copper fittings. Re-assemble the copper pipes, & copper fittings once all fluxed. The flux acid, cleans the copper surface, as you heat the joint, and keeps out oxygen(thus preventing oxidation), enabling the solder to flow evenly.

Tip – use a high quality silver tinning flux and applicator. It will cause the solder, to flow easily, into the copper pipe, & copper fittings. Note: water soluble flux is code in most places.

Tip– Only polish and flux what you will solder today. The acid of the flux will cause oxidation overnight.

Step 7: Soldering Copper Pipe

Soldering Copper PipeGet ready for sweating copper pipe. Be sure to keep heat away from all flammable materials near each copper piece, including framing, wires, and insulation. Cover the combustible materials with copper or steel sheet  metal, or fireproof cloth. Then, unwind about 10 inches of your roll of silver solder. Bend the last 2.5 inches in an 80-degree angle. Light your propane or map torch and adjust to a 1.5″ flame. Heat the copper fitting, with the torch, where the copper pipe fits into it. Utilize the inner flame, and move it around somewhat, so that it heats the whole fitting cup area. After heating for approx 10 seconds, melt the solder onto the joint at its highest elevation. If it is hot enough, capillary action, will suck solder right into the joint. If solder does not, go into the joint, apply more  torch, and try, try again. When solder drips out of the bottom of the copper fitting, the joint is adequately full of solder.

Tip – using the best silver solder will make your copper pipe sweating flow more smoothly. Buy lead free solder that mostly contains silver. The silver solder sticks to the copper fitting joint. Silver solder flows at a lower temperature, thus, less heating is required, and there is a longer flow time.

Step 8: Brush off excess solder

Quickly brush off excess solder, from around the joint, with a damp cloth for a professional finish. But, be careful; the joint is still hot.

Final Step: Test your system

Once all joints are soldered, and cool, you can now test your system. Open valve and faucets to bleed out  air. Check for leaks. If you encounter leaks, you will need to re-sweat  the leaking copper joints. Be sure to wash the outside and flush the inside of the copper joints to prevent copper oxidation.

Tip– be sure to drain all water; otherwise the water will boil and  prevent the fitting, from heating up enough to liquefy the solder. Try to reheat and apply new silver solder. If the it still leaks, you may need to replace the defective copper fitting or copper pipe.


Advanced Soldering Copper Pipe
How to sweat copper pipe

Advanced solder technique for larger joints: For horizontal joints, apply the solder, off-center, at the bottom of the joint. When, solder begins to melt, push the solder straight into the joint, while keeping the heat at the bottom of the fitting and slightly ahead of  the solder application. Continue this technique across the base of the fitting and up each side to the top of the fitting, overlapping slightly each time between the already applied solder and the new work. Small solder drops may appear at the solder application point, thus the joint is full of solder.

FYI, The solidified solder, at the joint base, makes a dam, to limit the solder from falling out of the joint as the joint is being filled.

Note: the solder will follow the heat.

For vertical position joints, use a similar series of overlapping passes, starting, wherever is easiest.

This technique takes a bit more practice…..


Soldering Torch: The basic soldering tool is a torch, consisting of one regulator, tube,  and a tip combination, that screws onto the top of a small propane tank. In order to use the torch, slowly open the fuel valve and light the tip of the torch. A regulator that has a built-in clicker finger actuated igniter works the best by far, its worth the extra few $$.

You can also use  a striker as well. Squeezing the steel handle pushes the flint over rough metal to make sparks, which ignite the gas. Don’t use matches.

Safety Equipment:

Safety Glasses, Always use leather gloves to prevent burns and cuts. Since you may turn the water off to work on the plumbing, be sure to have a bucket of water AND a fire extinguisher handy in case of fire. Use of a flame protector cloth is a wise investment. Using a spray bottle to wet flammables is a good idea.

What to tubing type to use for soldering copper pipe?

Find the correct copper tubing diameter. Copper pipe used for plumbing is nominally sized, ie: the outside diameter of the tubing is approximately 1/8″ (0.125 inches) bigger, than its stated size. Therefore, 1/2″ nominal copper pipe is about 5/8″ inches, of diameter.

But, is the pipe the right wall thickness, for your project?

Most nominal copper pipe is available in four weights or four wall thicknesses, which are all color-coded. Interior residential projects will mostly involve copper pipe, of two wall thicknesses: Type M or L.

‘L’ wall thickness pipe is marked with a medium blue writing on the pipe and is the most commonly used wall thickness for plumbing. Type L pipe wall thickness is thicker than type M. A hot water heater would still use type L piping since it is not air bled and thus is exposed to oxidation.

‘M’ wall thickness is marked in red writing on the pipe and has the lightest wall thickness,  that can be used for a pressurized system. It is typically used for hydronic(water) heating systems with a closed loop. The closed loop hydronic system has air bleeder valves and thus removes oxygen from the system. The absence of air reduces corrosion in the pipe over the years and thus enables the safe use of the lighter pipe.

DWV pipe is for ‘drain waste vent’ systems and is only used for drains. Since copper is expensive, the DWV piping is used infrequently. Also, it may contain small amounts of lead and thus not appropriate for USP water use, aka, don’t drink the stuff!

Type K copper pipes have even thicker walls than Type L or Type M. Type ‘K’ pipe is normally used to water distribution, fire protection,  HVAC, and oil. K copper pipe is not to be used for natural gas applications, as the gas, can damage joints. K Copper pipe joints, use either flared or compression fittings; ‘K’ tubing is thicker and thus recommended  for underground installations like water line mains.

Type K,M,L piping are available in either soft or hard varieties. M & L piping are usually hard. Refrigeration tubing is usually soft.

Get the correct fittings and joints for your project.

Female & male adapters,  are used to join a soldered pipe to a threaded fitting or pipe.

Reducing adapters or tubing adapters,  are used to go from a smaller size pipe up to a larger pipe.

Street fittings are fitting sized on one end and pipe sized on the other end.

Elbows are used to turn the piping, available in 90 degree bends, 45 degree bends, and sometimes 22.5.

Tees and Wyes are used to join branch piping to the pipe main; a double tee or cross tee or double wye has two branch piping outlets.

What types of Solder are there?

There are several types of solder available on the market, most not suitable for USP or potable(drinking) water. (Solder is pronounced like “sod-er,” not soldier btw.)

  • Lead solder is made of, or contains lead, and is used for many legal applications such as joining copper drainage pipe(DWV), electrical copper, and copper roofing. Its usually a 50/50 mix of tin and lead. It melts at a relatively low temperature and adheres easily to the copper. Be careful, lead is poisonous, treat it as such while using and disposing. Also some municipalities, like San Francisco, have outlawed all lead uses, check with local building departments. The 1986 amendment to the Federal Safe Drinking Water Act (SDWA) banned solders containing lead at concentrations of greater than 0.2% for all potable water systems.
  • Roof solder is different than other solders for two reasons:  it contains lead and it comes in 50/50(tin/lead) bars, not as coiled wire. Also the technique typically used a flat electric iron instead of an open flame to heat up the copper: safer. Heat up the copper and then apply the solder to where the heat was not where it is. Slowly draw the iron parallel to the joint. The final project should look like a ribbon of mercury after the joint is complete and sealed. Caution: most municipalities are outlawing lead roof solder.
  • Electric solder is also unique. It also contains 50/50 lead/tin ratio, but it has a flux rosin core running down the center of the solder wire(its hollow). Soldering makes a better and more durable electrical connection than wire nuts. Don’t use acid core for copper plumbing joints, it will ruin your joints.

Plumbing  Solder: Must be lead free. Don’t buy the cheapest.

Copper pipe silver solder

I’ve had good luck with a product called ‘100% Watersafe.’ It has a higher silver content for strength and flowability; melting point is 418-440 degrees F. A silver/  copper / tin enhanced alloy. You get 25% more feet of solder per pound than 50/50. Lead, zinc, arsenic, cadmium, and nickel free and meets ASTM-B32. Great for sweating copper joints.

Lead and silver free solder is cheaper but you will need such a high temperature that you can blacken and oxidize the pipe before the solder melts(you have to use the hotter MAPP gas not propane)….and the high temp stuff does not flow and seal as well either. Unfortunately the good stuff is about twice the cost, but you make this up after the first cheap stuff solder joint that leaks.

High Temperature and Pressure Note:

Continuous operation at temperatures exceeding 250°F, or where the highest joint strength is required, use brazing not solder for joining pipes and fittings. At higher pressures, or, for greater joint strength, use silver solder.

Ventilation Caution: The burning flux makes a smoky stink and lead fumes are extremely poisonous. Be sure to either solder outside or provide adequate ventilation with fans, ect, per OSHA standards.

Helpful Links:

Soldering copper pipe per building code must follow ASTM: B32 –,