How to Solder Copper Pipe (Step by Step)
Learning how to solder copper pipe is one of the most useful DIY plumbing skills a homeowner can pick up. A properly soldered copper joint, also called a sweat joint, can last 50 years or more without leaking, and the tools cost less than a single plumber visit. This guide walks you through the whole process in plain English, from cutting and cleaning the pipe to heating the joint and feeding the solder, so your first joint comes out watertight.
What You Need to Solder Copper Pipe
Before you light a torch, gather everything you will need. The basic kit is small and inexpensive: a propane or MAPP gas torch, lead-free solder, flux and a flux brush, emery cloth or a pipe-cleaning brush, a tubing cutter, a deburring tool, and a heat shield or fire-resistant cloth. You will also want safety glasses, work gloves, and a spray bottle of water or a fire extinguisher nearby. Most homeowners can buy the full kit for $60 to $120 in 2026, and the torch and cutter last for years.
The solder matters more than most beginners realize. Since 2014, federal law has required lead-free solder on any pipe that carries drinking water, and the standard choice today is 95/5 tin-antimony solder or a silver-bearing lead-free alloy. Old 50/50 tin-lead solder is still sold for non-potable work, but it must never be used on drinking-water lines. Check the label before you buy. Water-soluble flux is the easiest choice for beginners because it cleans up with a damp rag, while petroleum-based flux works fine too but needs more cleanup.
Your torch choice affects how fast joints heat up. A basic propane torch handles 1/2-inch and 3/4-inch pipe, which covers most home repairs, but it works slowly on 1-inch pipe and larger. MAPP gas burns hotter and is worth the extra cost if you are soldering several joints or working with larger pipe. Either way, buy a torch with a trigger-start igniter so you are not fumbling with a lighter near an open flame. If you are working near wood framing, a heat shield cloth is not optional — it protects studs and joists from scorching.
Step 1: Cut and Clean the Pipe
Start by shutting off the water and draining the line you are working on. Even a small trickle of water inside the pipe will steal heat from the joint and prevent the solder from flowing, which is the single most common cause of failed joints. Open a faucet at the lowest point in the house and one at the highest point to let the line drain fully. If water keeps seeping through, stuff a small piece of white bread into the pipe upstream of the joint — it temporarily blocks the water and dissolves once the water is turned back on.
Cut the pipe square with a tubing cutter, not a hacksaw. Tighten the cutter wheel gradually, rotating around the pipe and tightening a quarter turn each pass, until the pipe separates cleanly. A square cut matters because a crooked cut leaves a gap inside the fitting that solder cannot bridge. After cutting, ream the inside of the pipe with the deburring tool on your cutter to remove the burr, and smooth the outside edge with emery cloth.
Cleaning is the step beginners skip and professionals never do. Polish the outside of the pipe end and the inside of the fitting socket with emery cloth or a fitting brush until the copper is bright and shiny, with no dull spots or green corrosion left. Solder will not bond to dirty or oxidized copper, full stop. Wipe away the dust with a clean dry rag. Do not touch the cleaned surfaces with bare hands afterward, because skin oil can interfere with the bond. If you are repairing an old line, you may need to sand harder or use a wire brush to get through years of oxidation.
Step 2: Dry-Fit and Apply Flux
Slide the fitting onto the pipe and check the fit before you apply any flux. The pipe should slide in snugly with a little resistance. If it is loose and wobbles, the fitting may be the wrong size or worn, and no amount of solder will fix a sloppy fit. If it will not go on at all, check for a burr or a dent in the pipe end. Dry-fitting also lets you confirm angles and measurements before anything is permanent, which matters when you are assembling several fittings in a tight space.
Once the fit is right, take the joint apart and brush a thin, even layer of flux onto the outside of the pipe end and the inside of the fitting socket. Flux does two jobs: it cleans the metal as it heats and it helps the solder flow into the joint by capillary action. Use a thin coat — a thick glob of flux burns, leaves residue inside the pipe, and can actually block solder from flowing. Reassemble the joint with a slight twisting motion to spread the flux evenly, and wipe away any excess that squeezes out.
Assemble the full run of pipe and fittings before you solder anything. Soldering one joint can heat a nearby fitting enough to melt its solder, so plan the order of your joints and work from one end to the other. Leave the assembly supported so nothing moves while you work — a joint that shifts while the solder is cooling will leak. For more on choosing the right pipe for the job, see our guide to types of plumbing pipes.
Step 3: Heat the Joint Evenly
Light the torch and adjust it to a steady blue flame with a small, well-defined inner cone. Hold the flame so the tip of the inner cone is about an inch from the fitting, and move it slowly around the fitting, heating all sides evenly. Heat the fitting, not the pipe and not the solder — the fitting is the heavier piece of metal, and heating it draws solder into the joint. On a 1/2-inch joint this usually takes 10 to 20 seconds; a 3/4-inch joint takes a little longer.
Keep the flame moving. Holding it in one spot overheats the flux, burns it away, and leaves a scorched joint that will not take solder. You will know the joint is hot enough when the flux starts to bubble and then goes quiet and clear, and a touch of solder to the joint melts instantly on contact. If the solder balls up instead of melting, the joint is not hot enough yet. If you see smoke and the copper starts to discolor, you have overheated it — let it cool, clean it, re-flux, and start over.
Protect everything around the joint. Hold a heat shield cloth behind the fitting when you are working inside a wall cavity, and keep the flame away from plastic pipe, wiring, and insulation. Copper conducts heat surprisingly far along the pipe, so a fitting a foot away can get hot enough to melt. If you are soldering near a shutoff valve or a plastic component, wrap a damp rag around the pipe between the joint and the component to act as a heat sink.
Step 4: Feed the Solder
Once the joint is hot enough, take the flame away and touch the tip of the solder wire to the seam where the pipe meets the fitting. The solder should melt immediately and get sucked into the joint by capillary action. Feed in about 1/2 inch of solder for a 1/2-inch joint and about 3/4 inch for a 3/4-inch joint — that is usually enough to fill the joint completely. You will see a thin, shiny ring of solder appear all the way around the seam when the joint is full.
Do not keep feeding solder once the ring appears. Extra solder does not make a stronger joint; it just drips inside the pipe, where it can restrict flow or break loose later. Do not move the flame back onto the joint while feeding solder either — the heat from the fitting is what melts the solder, and reheating a finished joint can melt the solder out. If the solder is not flowing, the joint is too cool, and you need to reheat it rather than force more solder in.
On vertical joints, feed the solder at the bottom of the seam first and work upward, letting capillary action pull it around. On horizontal joints, feed at the top and let gravity help. Either way, check that the shiny ring appears all the way around the joint. A gap in the ring means the joint did not fill, and you should reheat and add a small amount of solder to that spot while the joint is still warm. If the joint has already cooled, you will need to reheat the whole fitting to reflow the solder.
Step 5: Cool Down and Inspect
Let the joint cool naturally. Do not quench it with water or a wet rag — rapid cooling can crack the joint or create a weak bond, and it is one of the classic beginner mistakes. The joint will be cool enough to touch in a minute or two. While it is still warm, wipe the outside with a damp rag to remove flux residue, which is corrosive and will turn the copper green over time if left in place.
Inspect the joint before you turn the water back on. A good joint has a thin, even ring of solder around the entire seam, with no gaps, drips, or blobs. The copper should be clean, not blackened or scorched. If you see a gap in the ring, reheat the joint and add a little solder. If the joint looks like a melted blob with solder dripping down the pipe, you used too much heat or too much solder — it may still hold, but clean it up and watch it closely when you pressurize the line.
Turn the water back on slowly and check every joint for drips. A tiny weep at a joint usually means the joint did not fill completely. Sometimes a small leak will seal itself as minerals deposit, but do not count on it — drain the line, reheat the joint, and add solder while it is hot. If a joint leaks badly, the best fix is to cut it out and start over with a new fitting, since trying to patch a badly made joint rarely works.
Common Soldering Mistakes to Avoid
The most common mistake is soldering a joint with water still in the pipe. Even a slow drip absorbs enough heat to keep the solder from flowing, and the result is a cold joint that looks fine but leaks under pressure. Always drain the line completely, and use the bread trick or a pipe-freezing kit if a valve will not shut off fully. The second most common mistake is skipping the cleaning step — solder simply will not stick to oxidized copper, and no amount of heat fixes that.
Overheating is the third classic error. When flux burns away, the joint oxidizes while you are trying to solder it, and the solder beads up instead of flowing. If the copper turns dark blue or black, stop, let it cool, take the joint apart, clean both pieces again, re-flux, and try once more. Underheating is the opposite problem: the solder melts on the outside but never flows into the joint, leaving a joint that looks soldered but has no bond inside. The test is simple — solder should melt the instant it touches the fitting, not the flame.
Finally, do not use too much solder or too much flux. A joint needs only a small amount of each, and excess solder inside the pipe can narrow the opening and eventually cause a blockage. Excess flux leaves acidic residue that corrodes the pipe from the inside over time. If you are joining copper to another material instead, read our guide on how to connect PEX to copper and our guide to connecting ABS to PVC for the right transition fittings.
When to Call a Plumber Instead
Soldering is a great DIY skill, but some jobs belong to a professional. If the pipe is inside a finished wall with no access panel, if you are working on a gas line (never solder gas lines yourself), or if the main water line needs to be shut off at the street, call a plumber. The same goes for any job where a mistake would flood a finished room — the cost of a plumber is small compared with water damage repairs.
Also consider calling a professional if your first few practice joints keep failing. Buy a few cheap fittings and practice on scrap pipe before touching the real thing — an hour of practice on the workbench is worth more than any guide. Once you can make three clean joints in a row on scrap, you are ready for a real repair. If you would rather have a pro handle it, our plumbing pipe installation guide explains what to expect from a professional job, and you can reach a local plumber at (877) 762-1902.