Copper Soldering & ProPress

Copper is still the go-to material for commercial work, exposed runs, and anywhere the pipe needs to look good for decades. You can join it two ways. Soldering, also called sweating, uses heat and a filler metal. Press fittings use a tool to squeeze a sealing fitting onto the tube with no flame. Both make permanent joints when done correctly, and both fail in predictable ways when a step gets skipped. This is the plumbing-specific method. The general chemistry of solder and flux, and the hot work rules that apply near anything that burns, apply here too.

What You Will Be Able to Do

• Pick the right copper type and size for a water line
• Cut, ream, and clean tube so solder will take
• Solder a lead-free joint and judge whether it is good
• Make a press joint and find the usual causes of failure
• Decide between solder, press, and push-fit for a given job

Copper Types

Copper water tube comes in three wall thicknesses. The color of the printing tells you which is which.

Type L is the workhorse for interior supply in many areas. Many codes also allow Type M above ground, and some areas do not. Check before you buy. There is also a thinner DWV copper for drains only, seen mostly in older buildings. It is never used for water supply.

Copper comes hard-drawn in straight lengths or soft in coils. Soft copper bends around obstacles and is often used for underground runs and short connections.

Horizontal support for small copper is commonly every 6 feet. Larger tube can go farther, and the exact size break depends on your code. Vertical runs are usually supported at each floor, up to 10 feet.

Preparing the Tube

Soldering and pressing both start here, and most bad joints can be traced to this step.

1. Cut it square. Use a tubing cutter, not a hacksaw. Tighten the wheel a little with each turn around the tube. Cranking down hard crushes the tube out of round. Use a mini cutter in tight spots.
2. Ream it. Remove the burr inside and outside with the reamer on the cutter or a deburring tool. An inside burr disturbs the flow and can cause erosion over time. An outside burr keeps the fitting from seating and can tear a press fitting's O-ring.
3. Clean it. For solder, sand the outside of the tube about an inch back and brush the inside of the fitting until both are bright. A dull, oily, or tarnished surface will not take solder.
4. Keep it clean. Handle the tube by the middle, not the cleaned end. Oil from your skin is enough to stop solder from flowing.

Soldering a Joint

Flux and Solder

Flux does two jobs. It keeps the hot copper from forming oxides, and it helps solder wet the surface and pull into the joint by capillary action. Use a water-soluble flux labeled for potable water, and brush a thin, even coat on both the tube end and the inside of the fitting. Too much flux stays inside the pipe and can corrode it later.

The Safe Drinking Water Act limits solder and flux on drinking water lines to no more than 0.2 percent lead. Use solder labeled lead-free. Common choices are tin-antimony (95/5) and tin-silver-copper alloys. Solder with lead (50/50) must not be used on drinking water lines. If the label does not say lead-free, do not use it there.

The Procedure

Warning: Water in the line turns to steam, blows solder out of the joint, and can spray scalding water at you. Shut off the water and open a low faucet to drain the line before you heat anything.

1. Protect anything nearby that can burn. Put a flame shield behind the joint, have an extinguisher within reach, and follow the site's hot work rules.
2. Fit the joint together and twist it a quarter turn to spread the flux. Make sure the tube is fully seated.
3. Light the torch and adjust it to a sharp blue inner cone.
4. Aim the flame at the fitting, not the tube and not the solder. The fitting is thicker and needs to come up to temperature first. Move the flame around the whole fitting so it heats evenly.
5. Touch the solder to the joint on the side away from the flame. When the fitting is ready, the solder melts on contact and pulls into the joint. If you have to hold the solder in the flame, the fitting is not hot enough.
6. Feed solder until a bright ring shows around the whole joint. For 1/2-inch tube, about 1/2 inch of wire is enough. Extra solder only drips into the pipe.
7. Remove the heat and hold the joint still until the solder sets.
8. Wipe the joint with a damp rag while it is still warm to remove flux.

After the system is together, flush the line to clear leftover flux.

Stopping a trickle of water takes planning. Open a low point to drain the line. If water keeps coming, the valve may be leaking by. A small plug of white bread pushed into the pipe can hold back a trickle long enough to sweat the joint, and it flushes out later. Larger problems need a pipe-freezing kit or a new valve.

Reading a Soldered Joint

A leaky joint rarely gets better by adding solder over it. Take it apart, clean everything, and start over. If a fitting has been overheated, replace it.

Warning: Hot joints stay hot longer than they look. After any torch work, check the area for smoldering and keep watching as long as your site's fire watch rules require.

Press Fittings

A press fitting has a sealing element, usually an O-ring, inside the fitting. A battery-powered press tool squeezes the fitting onto the tube. There is no flame, which is the big advantage. ProPress is a well-known brand from Viega, and you will hear that name used for all copper press fittings.

Press fittings for copper are made to standards such as ASME B16.51 and IAPMO PS 117. They are not the same as push-fit fittings, which fall under ASSE 1061.

Making a Press Joint

1. Cut the tube square and ream it. Press fittings need a clean, round end too, even though they use no solder.
2. Wipe the tube end clean. Paint, thread sealant, or grit can stop the O-ring from sealing.
3. Check that the O-ring is in place and undamaged.
4. Mark the insertion depth on the tube using the manufacturer's gauge or chart.
5. Push the tube fully into the fitting with a slight twist until the mark lines up with the fitting edge.
6. Choose the jaw that matches the fitting system and the tube size. Jaws are not interchangeable between systems.
7. Place the jaw squarely on the fitting's press bead and press the trigger. Let the tool finish the full cycle.
8. Inspect the joint and check your depth mark again.

The most common cause of a failed press joint is a tube that was not pushed all the way in. A half-seated tube can pass a quick look and then leak or pull out under pressure. A partial press from a dying battery is also a problem. You cannot fix a bad press by pressing over it. Cut the fitting out and use a new one.

Most press fittings are built to leak on purpose if they are left unpressed, so a pressure test finds any you missed. Always do the test.

Press joints are limited by the O-ring. The fitting must be rated for the fluid and temperature you are working with. Standard EPDM seals are fine for water but wrong for gas and oil, which use different seals and fittings. Check the listing.

When Press Beats Solder

Press fittings shine in occupied buildings, near combustible materials, and anywhere a torch would call for a hot work permit and a fire watch. With no flame, you have no ignition risk near framing, insulation, or finishes. A press joint is also fast and works on a line that is not completely dry, though the tube must still be clean and undamaged.

Push-Fit Fittings

A push-fit fitting grips the tube with teeth and seals with an O-ring. All you need is a clean cut, a deburred end, and a depth mark. They are made for quick repairs and tight spots. Whether they are allowed inside finished walls depends on your jurisdiction, and many inspectors restrict them there. Check with your authority having jurisdiction (AHJ) before you close a wall. A push-fit fitting also needs a tube free of deep scratches, or the O-ring can leak.

Choosing a Method

Common Mistakes

Check Your Understanding

1. You touch solder to a heated joint and it beads up and rolls off. What are the two likely causes?

Either the copper was not clean enough, or the fitting is not hot enough. Let it cool, take it apart, clean both surfaces, reflux, and try again.

2. You need to tie into a line in an occupied office above a drop ceiling full of old insulation. Solder or press?

Press. There is no flame near combustible material, and you may avoid a hot work permit and a fire watch. Your site rules still apply.

3. A press joint leaked at the pressure test, even though it looks pressed. What do you check first?

Check the depth mark. The most likely problem is that the tube never reached full depth. Cut the fitting out and replace it. You cannot press it again.

4. A coworker hands you a roll of 50/50 solder to repair a kitchen supply line. What do you say?

No. 50/50 contains lead and cannot be used on a drinking water line. Use solder labeled lead-free.

Key Takeaways

• Clean, bright copper is the difference between a good joint and a leak.
• Drain the line before you solder. Steam ruins joints and burns people.
• Heat the fitting, and let the hot fitting melt the solder.
• Use lead-free solder and flux on all drinking water lines.
• Press joints fail most often because the tube was not fully inserted, so mark your depth.
• Press and push-fit fittings have limits. Check the listing and ask your AHJ.