How To Solder Wet Copper Pipe: 5 Things You Must Know

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In general, people know that soldering can be a demanding and hazardous process. Because it involves super-heating the metal, soldering usually is only performed on dry metal to avoid creating steam and stopping the metal from reaching the desired temperature. But, what if you need to solder copper pipes with water in them?

This article lists the five main things to know about how to solder wet copper pipes, including:

  • Plug the water
  • Find the right temperature
  • Sweat the copper
  • Using soldering paste to hasten the project
  • Using a damp cloth on the joints

Although it is usually recommended to only solder copper pipes that are completely dry, sometimes you need to fix one of your water pipes in the house. Things do not always work as intended, and you need to be prepared to work under less than ideal conditions. If you want to know what to keep in mind when you solder wet copper pipes, read on. 

How To Solder Wet Copper Pipes

Soldering wet pipes of any kind is a tricky business, but your first task is to get them as dry as you possibly can. We will cover the types of plugs that people commonly use to stop the water after the valve is shut off and the soldering process in detail below. The most important part of soldering is making sure you have the right materials for the job. 

Once you have these tools on hand, you are ready to begin soldering wet copper. Always remember to take any safety precautions that you need to before starting a soldering project. You will be working with an open flame, so gloves and eye protection are the bare minima of safety requirements required to keep you protected while you work. 

You will also need to make the same preparations with your copper pipe as you would usually when getting ready for any kind of soldering project. That includes cleaning the portion of the tube you plan to solder and deburring the inside of the pipe with a combination of sandpaper and a wire brush. 

Obviously, you do not want anything like gunk or rust to be there still when you start soldering.

If your pipe is rusty, you will want to be quite careful when cleaning it because the rust makes the copper more brittle, and you might end up creating a tiny crack or hole if you scrub it too roughly. 


Before you begin soldering your wet copper pipes, you will need some equipment. Regardless of how wide your tube is, some necessary tools are required for any kind of soldering, so you should ensure that you have everything you need before you begin the project. No one wants to get started and then realize they are missing something crucial.

You will need the following:

  • Wire brushes
  • Fire extinguisher
  • Gloves
  • Tube cutters
  • Torch
  • Striker
  • Fuel
  • Sandpaper
  • Safety glasses
  • Flux
  • Solder

Wire Brushes

Despite your pipe’s watery contents, it should come as no surprise that gunk and other unpleasant stuff can build up inside of your line. You do not want that stuff getting in the way of your soldering material affixing itself to the pipe because it might cause a leak or make the fitting not watertight. 

Fire Extinguisher

You might only be using a tiny torch, but you should never underestimate the need for a fire extinguisher. Whenever you are working with an open flame, you need to have an extinguisher on hand. It is always better to be safe than sorry. 


These are especially important, not only because you are using an open flame and dealing with scorching metal, but also because of the acidic nature of flux. You do not want to get such a strong acid on your skin or anywhere else on your body. 

Tube Cutters

If you use a rotary cutter, you will end up leaving behind a small burr or lip inside of your pipe, right at the cut edge. You will need to use a sharp tool to take the burr off so that it does not reduce your water flow or cause the water pressure to build up inside the pipe and possibly cause leaks. 


It can be somewhat tricky to determine the best torch to use when soldering copper pipes. For pipes between ½ and ¾ of an inch wide, a pencil torch is perfectly capable of reaching the temperature you need if you have some patience. For many people, waiting an extra few seconds is more comfortable than trying to maneuver a larger open flame in a tight spot. 


Depending on the type of torch you use, it may not come with a lighter built-in. For example, most pencil torches will require the extra use of a striker to get the flame going at the beginning. 

You always want to make sure you have prepared as much as possible before starting the fire, but especially in cases when you have to light the fire every time manually, you do not want to have to keep turning off the torch and then groping around for the striker every single time. 


Propane and propene or MAPP Gas are your two options. Which one is better for copper pipe soldering? Well, MAPP Gas burns at a hotter temperature, so it is better for pipes wider than one inch. Otherwise, you can just use propane since it is often less expensive. 


Some people prefer to use an abrasive pad or sponge instead of sandpaper for this task. Other people cut off the tip of a wire brush and attach it to a power drill to speed up the process and thoroughly polish the fitting and the pipe ends attached to the fitting. However you want to clean them, just make sure you get every inch. 

Safety Glasses

These are essential and a piece of equipment that you should not skip. In addition to the open flame and hot metal, you will also be using acidic flux, and getting that on your skin or in your eyes is potentially devastating. Practicing proper safety precautions is essential whenever you engage in home projects and repairs. 

Flux (Soldering Paste)

There are many types to choose from, although beginners tend to prefer tinning flux. It is more expensive than average flux, but it makes it easier to avoid any leaks when soldering. You want to make sure that your flux does not contain lead if your pipe contains drinking water. 

Additionally, you want the flux to be able to be dissolved by water. Otherwise, it will build up in your pipe, which can cause blockages or leaks if too much water pressure builds up behind the flux after the valve has been turned back on. 


If you plan on repairing a pipe that contains drinking water, you will need to select solder material that does not have lead. The label should clearly state that the solder is safe for drinking water. If you do not see that on the label, exercise caution and use a different soldering material for your drinking water pipes.

Plug The Water

The first thing you need to do before anything else is to plug up the water. Drying out your copper pipe entirely may not be possible depending on how urgent your project is, but you at least want to stop any more water from interfering. Many different pipe plugs on the market will inhibit the flow of water down the pipe while you are busy soldering.

You will want to put the plug in far enough back to give you some elbow room for your soldering. If the section you are working on is as dry as possible, it will go a long way in aiding you as you work. In addition to plugging up the pipe, you will need to remember to shut off the water that flows to the line. 

If you leave it on, the water will build up in the pipe behind the plug, and your pipe may burst or crack from all of that water pressure, so remember to shut it off beforehand. If the water starts to leak out of the line or around your plug, you can put a bucket underneath to catch the errant water, just as long as it is not dripping into your workspace. 

As mentioned above, soldering metal that is actively wet or full of liquid is not recommended because the heat dissipates into the liquid and causes it to steam. The creation of steam steals the heat away and inhibits the metal from heating up to reach the temperature it needs to. 

Draining The Pipe

Before you can actually insert the plug, you will need to drill a tiny hole into the pipe and let out any water that is leftover inside the tube. Have a bucket on hand to catch the water so that it does not just splash all over you and the floor, and then set that water aside. 

Having turned off the water for the house, if there is an emergency with the torch, having a bucket of water in a convenient location in addition to a fire extinguisher may be a real life-saver. Once you have completely drained the pipe, you can get to work cutting the pipe and inserting the plug, as discussed in detail below. 

Plugging Up The Pipe

For people who do not have handy pipe plugs that are watertight, there are other DIY solutions that you can consider. Some people have used a large amount of chewing gum, moistened bread, or wax capsules as their make-shift pipe plugs. Whatever you choose to use, you will need to push the plug into the pipe with something long and thin, like a pen or knitting needle.

Just make sure that you can get the plug out again once your project is finished. Many a poor DIYer has ended up causing more damage to their pipes by clogging them with their improvised pasty plugs. As long as you can get the plug out again when you have finished soldering, you should be safe. 

For things like damp bread, most people bank on the fact that the renewed water pressure, once the valves are turned back on, will be forceful enough to flush the bread plug out of the pipe entirely. You want your plug to sop up any extra moisture without clogging the pipe. However, for people who do not want to take a chance, hardware stores sell pipe plugs.

These plugs have their own applicators and, at the end of the project, you can get rid of the plug with your soldering torch. All you have to do is heat up the area directly underneath the plug with the soldering torch, and the water plug should dissolve without a problem. A neat and simple solution if you are willing to spend the money on it. 

Find The Right Temperature

Speaking of temperature, you want to know precisely what your torch is capable of and set it to the optimal temperature based on the width of your pipe. Clearly, the larger the tube is, the more heat you will need to correctly solder it without allowing for leaks and a poor fitting. To find the right temperature, you will need to measure your pipe’s diameter.

Keep in mind that cleaning the inside of the pipe may increase its diameter, so it is better to measure it a second time after you have gone over it with your sandpaper and wire brush. A smaller pipe needs not only less heat but will need the heat applier for a shorter amount of time too. For example, a ½ inch pipe does best when you apply 3,500F of heat.

Your torch’s wattage tells you how hot it is capable of becoming. As a comparison, a torch with a wattage of 15 can achieve up to 550F, whereas a torch with a wattage of 40 can achieve more than 800F. Using anything over 500F will work, although most people prefer to use a torch capable of 750-800F for copper pipes. 

If you use a torch that is not capable of at least 500F, you may have to spend longer waiting for your pipe to heat up to the ideal temperature, so you might end up stuck in a crouched position, counting down the minutes as you keep the torch going.  

Sweat It Up

Once you have applied the soldering paste to the area, you plan to heat up, crank up your torch and listen to the paste sizzle and pop. You only need to scorch it for around five to ten seconds and then repeat the same process on the other side to make sure it is heating evenly. If you want to have a visual, you can gently touch one part of the soldering material to the pipe.

If the soldering material begins to melt upon contact, that means you have achieved the right temperature. Then you can put the fitting into the pipe. Please remember to assemble the pipe fitting before you start turning up the heat so that you will not have to spend precious moments fumbling around with the parts while your pipe cools down. 

After you put the fitting into the pipe, you can use a cloth to wipe away any excess flux that may have leaked out to the sides. If you notice that any parts are not completely sealed, you can apply more flux after the metal cools slightly and then reheat the area so that the flux melts into those cracks and affixes the fitting firmly to the pipe. 

Your Pipe’s Flux Capacity

Soldering paste, also known as flux, should be gently applied in a thin layer over the top of your pipe. The flux is an acidic substance that works to connect the solder and the line. If you repair a tube that holds drinking water, you will need to check that the flux you are using is safe for potable water, but many hardware stores sell flux, so you should not have any trouble finding it. 

Flux also serves to discourage the creation of rust in both the copper pipe and whatever solder you use. 

Use A Damp Cloth

This may seem counterintuitive since the whole reason that this job is more challenging than average is the presence of water, but using a damp cloth to protect the pipe’s joints is often recommended by experts. By wetting the fabric, it absorbs heat from your torch and stops the open flame from touching the protected parts underneath. 

In Conclusion

Now that you know the basics of soldering a copper pipe that currently holds water, you can roll up your sleeves and get to repairing those old pipes in the basement. You will not have to keep putting off the project and rolling your eyes at the exorbitant cost of getting a handyman out to your house; now you can be the handyman and solder that pipe!


How to Solder Copper Pipe With Water in It |

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