When it comes to plumbing, copper pipes are a popular choice for water supply lines. Copper is durable, resistant to corrosion and has antimicrobial properties. However, copper pipes need to be properly joined together, usually with solder. Choosing the right solder is important to create strong joints that will last and avoid health hazards like lead contamination. So what solder is best to use with copper pipes? There are a few key factors to consider when selecting solder for copper plumbing.
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Lead-Free vs Leaded Solder
One of the most important considerations when choosing solder is whether you want lead-free or leaded solder. Lead solder was commonly used in the past. However, due to health concerns, lead-free solders are now recommended for drinking water plumbing.
Lead Solder
Lead solder contains about 50% lead. The lead makes the solder easy to work with and creates reliable joints. However, lead is toxic and can leach from pipes into drinking water, causing lead poisoning. This is especially concerning for children who are more susceptible to lead’s neurological effects. Due to these health risks, lead solder was banned for drinking water systems in the US in 1986. Lead solder is still allowed for other applications like electronics.
Lead-Free Solder
Lead-free solders provide a safer option for copper plumbing. Instead of lead, they contain other metals like tin, silver, copper and bismuth. Lead-free solder meets health standards for contact with drinking water. There are different lead-free solder alloys on the market, but common options include:
– 95/5 Tin Antimony solder: Contains 95% tin and 5% antimony. This popular lead-free solder has similar working properties to lead solder. The antimony strengthens the joints.
– Silver-Tin solder: Contains 3-4% silver and the rest tin. The silver improves strength and flow.
– Copper-Tin solder: Contains 15% copper, remainder tin. Offers decent flow while minimizing cost.
So in summary, lead-free solders are the way to go for any new copper plumbing, especially for drinking water. While more expensive, they eliminate the risks of lead leaching and provide safer, reliable joints.
Solder Type
In addition to lead vs lead-free composition, solders come in different forms including wire, bar, and paste. Each has their advantages for particular soldering jobs.
Wire Solder
Wire solder consists of a hollow core flux with a wire of solder alloy wrapped around it. To use it, you cut off sections of wire as needed and melt them against the copper joint. The inner core of flux helps clean and join the metals. Wire solder provides an easy way to portion out solder as needed. It allows good control of the solder amount for small joints.
Bar Solder
Bar solder comes as solid sticks or bars of solder metal alloy. To use them, you melt the end of the bar with a torch and apply the melted solder to the copper joint. Bar solder is suitable for larger soldering jobs where you need a greater quantity of solder. It provides an economical way to buy solder in bulk. You can wrap up and save any unused solder for next time.
Paste Solder
Paste solder comes in tubes or syringes of flux paste with solder powder mixed in. To use it, you squeeze out paste onto the joint and heat it until melted. Paste solder offers the convenience of an all-in-one flux and solder formula. The paste consistency can make it easier to apply on vertical or inverted joints. However, paste solder may dry out over time in storage. It also typically costs more than wire or bar solder.
Which is Best?
For occasional, small soldering jobs on copper pipes, wire solder provides a handy, measured way to apply solder. For larger copper joints or whole plumbing systems, bar solder is often the most economical choice. Paste solder is great for tricky joints but costs more. Ultimately, the best type comes down to the specific project and preference.
Solder Diameter
Solder for copper plumbing comes in a range of diameters. The diameter required depends on the size of the copper pipes being joined.
Pipe Size
Common standard pipe sizes for copper plumbing include:
– 1/4 inch (often used for appliance connections)
– 3/8 inch (common branch and supply lines)
– 1/2 inch (frequently used for main water lines)
– 3/4 inch (sometimes used for main lines and risers)
Larger commercial sizes like 1 inch to 2 inches are also available.
Solder Diameter
As a general rule, the solder diameter should be close to the same size as the copper pipe inner diameter. This helps ensure the solder fully fills the cup of the fitting and makes a complete joint.
Some common solder diameters for copper pipe are:
– 1/8 inch solder – for 1/4 inch pipe
– 3/8 inch solder – for 3/8 inch pipe
– 1/2 inch solder – for 1/2 inch pipe
– 5/8 inch solder – for 3/4 inch pipe
Using too small of a solder diameter can result in leaks and weak joints. Too large of a diameter can cause excessive buildup and clogged pipes. Matching the pipe and solder size helps optimize the joint.
Solder Flux Types
Flux plays a crucial role in soldering copper pipes. Flux removes surface oxides and impurities, allowing the solder to adhere and flow. The right type of soldering flux makes the joints strong and prevent leaks.
Acid Flux
Traditional acid fluxes contain zinc chloride, hydrochloric acid, and ammonium chloride. Acid fluxes are highly active and efficient at cleaning copper and removing oxides for solid joints. However, they are also corrosive and can damage pipes if not fully washed out after soldering.
Non-Acid Flux
Non-acid fluxes provide a safer option for copper plumbing systems. As the name suggests, non-acid fluxes don’t contain harsh acids. Instead, they use organic acids and/or synthetic resins to remove oxides and prevent re-oxidation during soldering. While not as aggressive as acid fluxes, non-acid types still allow for quality solder joints when used properly. They are recommended for drinking water systems.
Both Work
Both acid and non-acid fluxes can work well for copper pipe soldering. But the non-corrosive, non-acid option is best to avoid long-term corrosion issues in installed plumbing systems. It provides a good balance of joint strength and safety. Be sure to carefully follow manufacturer’s directions for cleaning and flushing non-acid fluxes after installation.
Solder Alloy Composition
The specific metals contained in solder determine properties like joint strength, melting point, and flowability. Common alloy compositions used in lead-free solder for copper plumbing include:
95/5 Tin Antimony
– 95% tin
– 5% antimony
Advantages:
– Low melting point for easy application
– Good tensile strength
– Flows and joints well like lead solder
96.5/3/0.5 Tin Silver Copper
– 96.5% tin
– 3% silver
– 0.5% copper
Advantages:
– Higher strength than plain tin-antimony solder
– Excellent flow with thorough joint penetration
– Resists fatigue and vibration failure
99.3/0.7 Tin Copper
– 99.3% tin
– 0.7% copper
Advantages:
– Cost-effective tin-copper alloy
– Good balance of moderate flow and joint strength
– Low melting temperature
Generally, solders with 1.5-3% silver offer the best performance. But less expensive tin-copper alloys also produce adequate joints. The optimal alloy comes down to the specific project requirements.
Recommendations
Based on the factors discussed, here are some recommended solders for copper pipe plumbing:
For Drinking Water Systems
– Lead-free alloy like 95/5 tin-antimony or tin-silver-copper
– Match solder diameter to pipe size
– Non-acid, non-corrosive flux
– Conformance to NSF 61/ASTM B32 specifications
For Heating/Cooling or Condensate Pipes
– Lead-free tin-antimony, tin-silver-copper or tin-copper alloys
– Non-acid or acid flux depending on install/cleanup convenience
– Wire, bar or paste flux-cored solder
For Other Low-Pressure Applications
– Tin-antimony alloys for easiest application
– Appropriately matched solder diameter
– Economical non-acid flux
Proper soldering technique is also important – clean pipes, apply flux, overheat solder, allow proper cool time, and thoroughly flush systems after install. With the right solder choice and proper procedures, strong and durable solder joints can be achieved for a copper plumbing system.
Conclusion
Choosing the optimal solder for copper pipes depends on the specific project and application. But when health and safety are priorities, lead-free solders with non-corrosive fluxes are highly recommended, especially for drinking water systems. Tin-antimony and tin-silver-copper alloys offer time-tested lead-free choices that produce strong joints when used correctly. Matching solder diameter to pipe size also ensures a solid connection. With quality lead-free solder and proper technique, long-lasting and leak-free joints can be achieved for copper plumbing.