How to Expertly Solder Low-Lead Brass Using Tinning Flux

Tinning Flux is particularly useful to solder low- or no-lead brass effectively. Generally, lead brass conducts heat better than metals used today. However, most older, lead-piping systems have been eliminated, because research has shown that lead in water pipes can harm the human body through repeated exposure. The Environmental Protection Agency determined that drinking water's maximum lead-contaminant level should be zero due to its toxicity.

Soldering low lead brass can be daunting, since it doesn't conduct heat well. Using tinning flux will help eliminate the human error of soldering low-lead brass and help fill the joint to create a leak-free connection.

Let's explore how tinning flux helps the soldering process, how to apply it, and the types of tinning flux available at your supply house or local hardware store.

What is tinning flux and how does it help?

Unlike other flux formulas on the market, tinning flux contains ground-up solder flakes, known as tinning powder, that clean, tin and flux most commonly soldered metals, including copper, brass, zinc, galvanized iron lead and tin or copper-coated metals.

Tinning powder particles enhance the flux formula to pre-tin piping and improve the solder flow, enabling even heating of a fitting. The latter is necessary when soldering larger diameter piping systems.

Flux provides superior wetting properties for better solder flow. It also prevents oxidation by filling the joint and blocking air from entering during the wetting process.

Note: Tinning flux is not meant for use with aluminum, stainless steel or magnesium. Also, take care not to use it in electrical parts. We do not recommend Oatey flux and solders for aluminum, because it conducts heat so well that it is difficult to keep it warm enough to actually solder. Stainless steel should be brazed or welded. Consult the Oatey Technical Department for applications not specifically referenced here.

How to use tinning flux during the soldering process

Step 1: Preparation

It's important to clean all surfaces before soldering. Deburr (or ream) the inside of the pipe ends, using a deburring tool to remove any sharp edges and small bumps or roughness (known as burrs.) Deburring creates a smooth surface, ensuring less resistance to the water flow.

During prep, clean the fitting hub and the pipe with either a fitting brush or an abrasive sand cloth for larger diameter pipes.

Step 2: Apply the tinning flux

Apply a small amount of tinning flux inside the fitting and outside the pipe with an acid brush. Don't overdo it, as it requires only a thin layer on both surfaces.

Apply the flux with a brush: Do not apply it with your fingers and be sure to wash your hands thoroughly after use.

Use a damp cloth to remove any excess flux from the pipe and inside the fitting before connecting them.

Important: Never flux a pipe that will not be soldered within four hours. Flux is an acid and will have an etching effect if left on the pipe too long without heat and solder being applied.

Step 3:  Heat to temperature required for soldering

Do not overheat the piping:

  • For small-diameter piping, direct the heat near the joint.
  • For large-diameter piping, move the heat around the joint to ensure adequate solder flow around the circumference of the joint.

Note: Oatey considers pipes in a home to be large-diameter if they are 32mm (1.25 inches) or greater.

Since low-lead brass doesn't conduct heat as well, start by heating the pipe a little bit right outside of the hub or directly at the joint until the flux starts to bubble or activate. Then apply heat to the base of the fitting.

Applying heat to both the pipe and the fitting will ensure the most effective joint down the line, because solder follows the flux, which will flow towards heat. This method will allow the flux or solder to get drawn towards the base of the fitting, which, in turn, fills the entire fitting.

When applying heat, make sure you remove the flame as soon as the solder melts. As the solder melts, the flux will pull the solder into the fitting cup. Too much heat will either cause excess solder flow or burn off the flux, which will increase the chance of a leak path.

Read our blog to learn how to solder copper pipe and common mistakes to avoid to ensure a leak-free joint.

Step 4: Wipe off any excess flux

While the joint is still warm, immediately wipe away any residual flux or solder drips with a dry rag.

Wiping off excess flux is easy to skip, but don't. Failure to wipe away excess flux will result in severe pipe damage over time.

Any flux sitting in the pipe will eat away at the copper. It can also cause Verdigris — a greenish-blue discoloration commonly found on copper, bronze and brass — to form and destroy copper pipe over time. Eventually (it might be 20 years down the line), it will cause pitting and create a leak.

Types of Tinning Flux

Water-soluble tinning flux is water-flushable flux containing solder powder to aid in the soldering process. It is good for large-diameter copper piping and will not turn copper piping green.

Water-soluble tinning flux will flush out of the line when running normal water and is compatible with all common plumbing solder alloys. Water-soluble flux is less corrosive and self-cleans on the pipe's interior as water flows through the lines. It has a narrower temperature range when heating, but it works with all common plumbing solder alloys.

Petrolatum-based tinning flux (non-soluble flux) also contains tinning powder to help pre-tin the pipe to provide superior wetting properties for better solder flow. It cleans, tins and fluxes most commonly soldered metals, such as copper, copper-coated metals, brass, zinc, galvanized iron, lead and tin. With a petrolatum-based tinning flux, it's required to flush the line with a trisodium phosphate cleaner, due to their water insolubility. 

Fluxing is a critical step in the soldering process. Using tinning flux is particularly helpful when you are soldering larger-diameter pipes, because it acts as a primer and helps fill pipe joints completely.

Tinning flux is also helpful for homeowners or tradesmen who haven't done a lot of soldering, as it provides added protection to the pipe joint.

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