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How to Solder a Water Supply Line Installation

Water Supply Line Installation Tips

High Anxiety

Many a homeowner backs away from soldering copper pipe. The torch, molten solder, leaks, high pressure, etc. cause one to hesitate. Heck, isn't that one reason why plumbers make so much money? Well, I'm a plumber and I'm here to tell you that with a little knowledge and one or two practice joints, you can successfully solder leak-free joints in copper tubing.Yes, the process is dangerous, you can cause fires, you can burn yourself (I have various deep scars from serious third degree burns), however, I can't recall reading a story in the paper about a homeowner who drowned from repairing a copper line. If you do fail, so what? Call the plumber to bail you out (figuratively speaking of course!)

The Basics

To solder copper pipe you must heat the copper pipe and the fitting to be soldered to a sufficient temperature. When the copper is hot enough, it will actually draw the solder into the joint by capillary attraction. Believe it or not, solder will actually flow uphill. A simple propane torch that uses screw-on bottles will adequately solder pipe up to 3/4 inch in diameter. Plumbers generally use acetylene torches for two reasons. The acetylene burns hotter than propane, allowing for faster solder times. The acetylene is available in larger tanks which attach to handy hoses and lightweight torches. If you want acetylene, you just need to go to a large plumbing supply house or a place that services welders.

Clean Pipe & Fittings

Solder, which is available in leaded and no-lead versions, attaches to the pipe on a molecular level. The surface of the soldered joint actually becomes an alloy where the copper and solder intermix. For this to happen, the copper must be very clean and free of oxidation. You can clean copper pipe in any number of ways. You can use coarse steel wool, sandpaper and/or a wire brush. Special round wire brushes come in a variety of sizes to clean the inside of copper fittings and valves. Simply twist the brushes or pipe to clean them. Even if you purchase new copper pipe, it too should be cleaned. You only need to brighten the area which is to receive solder.

Flux - The Catalyst

Flux is a chemical which helps you solder. It actually finishes up the cleaning job you started with the sandpaper and brushes. In addition, it prevents the pipe from oxidizing as you heat it. You can solder without flux, but it is really difficult! Flux is applied to both the pipe and the fitting with a handy miniature paint brush. You do not need massive amounts to be effective. Besides, once you start to heat the pipe, 90 percent of it boils off and evaporates.

Solder - Different Types - Beware!

Solder is available in three types: 50 percent lead/50 percent tin; 95 percent tin-antimony/5 percent lead; and lead-free solder.

Any water supply pipe should be soldered with solder that contains no more than five percent lead. If possible, use the lead-free solder. The 50 percent lead solder is used for copper drain lines. It melts at a lower temperature and is able to bridge larger gaps as it cools. This is handy when working with large diameter (up to 4 inch!) copper pipe and fittings.You MUST pay attention when you buy solder. The 1 pound rolls look very much alike. Carefully look at the label as you might purchase the wrong one.

Lighting & Working with a Torch

Plumbing torches can be lit with matches, lighters or preferably a flint striker. Matches and lighters can be dangerous, as you might not put them out. A flint striker makes sparks which ignite the flame. Plus, a single flint in a striker can last a homeowner 10 years or more!

Flame temperature is important. You need to set the flame on medium or high to generate enough heat to melt solder. If your flame is adjusted correctly, it will burn different shades of blue. You will notice at the center of the flame a darker blue section that comes to a point. This is the hottest part of the flame. You apply this part of the flame to the copper pipe.

Don't be afraid to heat both sides of the pipe. Rotate the torch around the joint for even heat distribution. When I use my acetylene torch and I am soldering 1/2 inch pipe, I can usually heat the pipe to the correct temperature in 10 seconds or less. A propane torch may take 15 to 20 seconds.

Always look beyond the pipe. Extremely hot temperatures are beyond the visible portions of the flame. You can easily scorch lumber or wires. If you are soldering near old lumber or in joist spaces near vertical walls, you can easily start your house on fire. Be careful and use flame shields. These are flame resistant fabrics or simple pieces of sheet metal which absorb and/or deflect the heat.

Applying Solder

As you heat the pipe and fitting you will see the flux begin to boil and evaporate. Once the flux stops boiling the pipe is generally hot enough to solder. Move the torch away and touch the solder to the pipe. It may take 2 to 3 seconds for the solder to melt. If the pipe is horizontal, apply the solder to the top of the pipe. The solder will roll around in an instant. If you have done the job right, a droplet of solder will be at the bottom of the joint. You can flick this molten solder away with an old rag. Blowing on the joint will allow it to cool. It will be hot, but rub the joint quickly with an old rag to remove flux residue. This will also polish the solder. Check the joint closely to see if you see a silver-colored band around the entire joint. If so, your first solder joint may be perfect. As I would say on a job: Another quality installation!

Common Causes of Soldering Leaks

Virtually every soldering leak is a result of "operator error" - that is, it can be traced to some fault on your part. Here is a list of some of the most common causes for failure. Most are easy to correct. Some will give you problems.

Insufficient Soldering Temperature

This is the most common problem. Rookies and homeowners apply the torch to the joint to be soldered. They follow immediately with the solder. Within 2 to 3 seconds the solder melts from the intense torch heat. However, the copper pipe and fitting have yet to reach the necessary temperature to allow the solder to be drawn deeply into the joint.

Insufficient or Stingy Use of Solder

Often leaks result because just one side of the joint was soldered or the solder was not left on the joint long enough. Try to look at all sides of the joint after soldering. If you do not see a thin silver line where the fitting meets the pipe, you may have a problem!

Flux Failure

The solder paste or flux that helps the solder flow in the joint can cause problems. First, if you have not thoroughly stirred it before use, you can have a problem. The chemicals in the flux can separate, especially in hot weather. Also, you can get the flux too hot and burn the joint.

Dirty Pipes - Hand Grease

You must already get the message that both the pipe and the fitting surfaces that are to accept solder must be perfectly clean. I have had problems where I touched a pipe surface with my hands before fluxing. The oil and grease from my hands fouled the pipe!

Water in the Lines

You can't solder copper pipe with water in the lines (unless you have a super powerful torch with a special tip.) The water acts as a heat sink. You can't get the pipe hot enough to melt the solder. A common problem is water that drains from above as you try to solder. Homeowners often can't trace the source. Well, you must open all valves to all fixtures and even flush the toilets! The best way I have found to evacuate the lines is to turn the main water valve off. Go to the top of the house and open all the faucets. Proceed to the basement opening valves on the way. Then open the lowest valve in the system. Had your plumber installed a boiler drain valve right next to the main water valve you could really do the job right! Just attach a hose to this and empty the water at a floor drain. This method allows you to get just about every bit of water from the lines.

Pressurizing the System too Early

If you have just one simple joint to solder, you can ruin it by turning on the water too quickly. You can actually blow air and water right through the hot, molten solder. I did this 20 years ago, I know!

It sometimes can take up to 20 or 30 seconds for a pipe to cool sufficiently. You can always cool it by pouring or spraying water on the pipe. Watch out for steam!

Column B380


2 Responses to How to Solder a Water Supply Line Installation

  1. I appreciate your column. I believe the lead standard in the US for solder for potable water is no more than 0.2% lead, rather than the 5% mentioned above.

  2. Great information!

    One question I have is about flushing the excess flux out of the water lines after installation. Is there a special procedure necessary?

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