Working copper pipe
Clean, dry and bright is the whole secret of a soldered joint. The rest is technique that comes quickly.
Clean is the whole job
A soldered joint works by capillary action pulling molten solder into the gap between pipe and fitting. That only happens if the solder wets the metal, and it will not wet copper oxide. So the pipe is abraded to bright metal and the fitting socket is brushed clean, every time.
Flux helps by dissolving the thin oxide that forms while you are working, and it is often mistaken for a cleaner. It is not. A dirty joint with plenty of flux still fails, usually a few weeks later under pressure.
- Bright metal, both parts
- Abrasive strip on the pipe, wire brush in the socket. Dull copper is oxidised copper.
- Clean past the socket
- Solder and flux travel with the heat. Cleaning only the covered part leaves oxide at the joint edge.
- Flux is not a cleaner
- It removes the oxide that forms during the job, not the oxide that was there before you started.
- Do not touch the cleaned end
- Skin oil is enough to stop solder wetting a patch. Handle the pipe further back.
Heating a joint correctly
Heat the fitting, not the solder and not the pipe alone. When the fitting is at temperature, touching solder to the joint mouth draws it in around the whole circumference in about a second, and you will see it flash.
Overheating is the common error. It burns the flux, which then stops working, and the joint will not take even though it is plainly hot enough. If a joint refuses to take solder, let it cool, clean it again, reflux it and start over.
- Heat the fitting
- The socket carries the heat into the gap. Playing the flame on the solder just melts it into a blob.
- Watch for the flash
- Solder drawn in disappears into the joint in about a second. That is the signal to stop.
- Overheating burns the flux
- A joint that will not take when clearly hot is over-fluxed and burnt. Cool, clean, reflux.
- Drain the pipe fully
- A trace of water in the pipe holds the temperature at 100 degrees and the joint will never solder. This defeats everyone once.
Bending beats fitting
Every soldered elbow is two joints that can leak and a restriction to flow. A bend is neither, and on 15mm and 22mm a lever bender makes one in seconds. On a run with four corners that is eight fewer joints.
The former sets the radius and supports the wall while it goes round, which is what stops the bore flattening. Bending over your knee looks fine and reduces the bore more than you would think.
- Two fewer joints per corner
- Fewer leak paths, better flow, and less solder and less time.
- Always use a former
- It supports the wall. A freehand bend flattens the bore even when it looks acceptable.
- Measure to the centre of the bend
- Benders work around the mark rather than from it. The tool's own scale tells you where.
- Annealed pipe bends easier
- Soft coiled copper bends by hand with a spring. Half hard straight lengths need the bender.
When you cannot use a flame
In an occupied building, near a joist, or in a loft full of insulation, hot work is a genuine fire risk and often not permitted. Three systems avoid it entirely: compression, press fit and push fit.
Compression is cheap and fully serviceable, and it must stay accessible. Press fit is fast and permanent but needs an expensive tool. Push fit is the quickest of all and is the one most likely to be objected to on visible pipework.
- Compression
- An olive crushed between nut and fitting. Cheap, reusable fittings, and it must remain accessible for inspection.
- Press fit
- A crimped seal, permanent and fast. The tool cost is the barrier, not the fittings.
- Push fit
- An O ring and grab ring. Fastest of all, and check whether it is acceptable where it will be seen.
- Heat mat if you must solder
- Behind any joint near timber. A torch job can start a fire that shows itself hours later.
Compression joints and how they leak
A compression joint seals when the nut crushes a brass olive between the pipe and the fitting body. It needs the pipe cut square, deburred, and pushed fully home before the nut is tightened, and it needs the right amount of tightening.
The usual mistake is overtightening, which extrudes the olive and can split the nut. Hand tight plus about one full turn is the general rule, then a quarter turn more if it weeps. A joint that still weeps after that needs the olive replaced, not more force.
- Square and deburred
- The olive cannot seat evenly on an angled or burred end, and that is most compression leaks.
- Home before tightening
- Push the pipe fully to the shoulder. Tightening onto a partly inserted pipe seals nothing.
- One turn past hand tight
- Then a quarter more if needed. Beyond that you are extruding the olive, not sealing it.
- Two spanners
- One holding the body, one on the nut, or the pipe twists and the joint behind it loosens.
Frequently asked questions
- What tools do I need to work with copper pipe?
- A wheel pipe cutter, a deburring reamer, abrasive strip and fitting brushes, a lever bender, a blowtorch, lead free solder, flux and a heat mat. Add two adjustable spanners for compression fittings. That is a complete kit for domestic copper plumbing.
- Why will my copper joint not take solder?
- Three usual causes. The surface was not clean, so the solder cannot wet it. The joint was overheated and the flux has burnt. Or there is still water in the pipe, which holds the temperature at 100 degrees and no joint will solder at that. Drain fully and start again.
- Do I heat the solder or the fitting?
- The fitting. When it reaches temperature, touching the solder to the mouth of the joint draws it in around the whole circumference in about a second. Playing the flame on the solder just melts it into a blob that sits on the outside.
- Can I use lead solder on drinking water pipe?
- No. Lead solder is prohibited on potable water systems and has been for decades. Use lead free solder, which needs slightly more heat and behaves a little differently. Lead solder is still sold for non potable and electrical work, so read the label.
- How tight should a compression fitting be?
- Hand tight plus about one full turn with spanners, then a quarter turn more if it weeps. Beyond that you are extruding the olive rather than sealing it, and you can split the nut. If it still weeps, replace the olive rather than tightening further.
- Should I bend copper pipe or use elbows?
- Bend where you can. A bend has no joint to leak and restricts flow less than an elbow, and it saves two soldered connections per corner. Use fittings where the radius would be too tight for a bender or where there is no room to swing one.
- Are push fit fittings as good as soldered ones?
- For performance in service, modern push fit is rated for the same pressures and temperatures. They are bulkier, they cost more per joint, and some people object to them on visible pipework. Their real advantage is speed and no flame at all, which matters in an occupied building.
- What is a press fit tool and is it worth it?
- A tool that crimps a fitting permanently onto the pipe against an internal O ring, with no heat. It is fast and reliable, and the tool is expensive enough that it only makes sense for regular work or where hot work is not permitted at all.
