Fluxes and solders

Some concerns about using lead solder and applying fluxes incorrectly

The Manager of the Water Regulations Advisory Scheme has expressed concern regarding the illicit use of lead solder and the improper application of fluxes.

I have not received formal training as a plumber, and I write with some trepidation about the skills that should be second nature to all plumbers. However, recent observations have indicated that there is considerable room for improvement in the quality of plumbing work. The illicit use of lead solder and the improper application of flux have prompted concerns among water suppliers, plumbing associations, water fitting manufacturers, and health authorities regarding potential health risks.

Reasons for concern

In the past eighteen months, a young boy and his father, who had both been unwell for an extended period of time, consulted with their physician, who identified the presence of lead poisoning. The results of blood tests confirmed the diagnosis, and subsequent detective work revealed that the source of the lead poisoning was drinking water with excessive amounts of lead in it. The lead contamination originated from the use of lead-based solder in the jointing of the pipework.

The child was in the habit of taking a glass of water for nighttime consumption from a tap in an upstairs bathroom that was not frequently used. The father consumed a considerable amount of water at home and brought hot and cold beverages to work with him. The residence was not constructed with lead plumbing. The residence was constructed recently, subsequent to the enactment of the 1987 water supply bylaws, which prohibited the utilization of lead-based solders for the construction of hot and cold water systems. A subsequent survey indicated that over 15% of residences constructed up to three years prior had employed the use of lead solder in contravention of the relevant bylaws. This was not confined to a single estate, builder, or plumbing firm.

Ban on use of lead solder

In response to concerns about the potential health effects of even low levels of lead in drinking water, since the 1980s, the use of lead-based solder has been prohibited for installation on hot and cold water systems. Leaded solders may be employed in non-drinking water systems, such as closed circuit central heating pipework, where the water is not required to be wholesome. These requirements have been incorporated into the new Water Fittings Regulations (Water Byelaws 2000). It is the responsibility of water suppliers to ensure compliance with these regulations. In the event that the illicit use of lead-based solder is discovered in a drinking water system, the water supplier is likely to require the replacement of all joints at the installer’s expense. In addition, the installer may be subject to criminal prosecution and a fine.

Alternatives to lead solder

Push-fit and press-fit fittings represent alternative solutions to soldered joints. In instances where soldered joints are required or preferred, lead-free solders are available in the form of integral solder ring fittings or for end-feed use. The utilization of a solder such as number 23 tin/copper alloy soft solder, which has been manufactured in accordance with the specifications set forth in EN 29453, will ensure that the levels of lead present in the solder are within an acceptable range. In addition to its suitability for all soldering work, the aforementioned solder is less dense than lead solder, resulting in a greater volume per 500-gram reel. Consequently, there are more joints per reel.

Fluxes -good and bad

The application of flux facilitates the wetting, adhesion, and alloying of molten solder with the copper tube. The transition to lead-free solders, which have a higher melting point than their lead-based counterparts, necessitates the use of an appropriate flux. In the case of ordinary soft solder joints, fluxes based on zinc chloride or zinc ammonium chloride are typically employed. It is advisable to adhere to the manufacturers’ instructions. Modern fluxes, in particular self-cleaning varieties, may be more corrosive to copper tubes and thus require greater caution in their use. The overuse of flux can result in an accelerated corrosion rate of the pipework. In certain instances, elevated levels of copper and lead have been observed in water samples that have been in contact with poorly constructed joints that have accumulated excessive flux residues. Ultimately, excessive corrosion can result in the premature failure of the pipework and the occurrence of leaks.

Cleaning and fluxing

Once the cut tube end has been deburred on the interior and exterior, the exterior of the tube should be cleaned. The green abrasive impregnated nylon kitchen scouring pad is recommended for domestic use to avoid steel wool fragments in the system. It is imperative that flux not be applied to the fittings. Instead, a thin coating should be applied to the outside of the tube immediately following cleaning. It is recommended that the assembly be completed without delay to prevent contamination by dirt or dust. The flux should then be distributed internally by twisting the fitting onto the tube. Any excess flux should be wiped off. It is essential that the heating of the tube and fitting be even and that the temperature be maintained at a level sufficient to melt the solder, but not so high as to cause damage. It is important to note that temperatures exceeding this level may result in the flux being charred. For integral fittings, it is sufficient to apply gentle, even heat until a complete ring of solder appears at the mouth of the fitting. It is inadvisable to attempt to add additional solder to an integral ring fitting by means of an end feed. For end-feed joints, it is necessary to heat the tube and fitting to a sufficient temperature so that, once the heat source is removed, the solder will melt and flow into the joint when touched to the tube. It is advisable to avoid using excessive quantities of solder, as this may result in the soldering iron overheating and causing damage to the tube. For small tube joints, a length of solder wire equal to the diameter of the tube should be sufficient to fill the joint.


Once the joint has cooled, any residual flux on the exterior should be removed with warm water. The pipeline should be flushed to remove flux residues and any debris. For water-based fluxes, cold water is sufficient; however, for grease-based fluxes, hot water is preferable, as cold water may not effectively remove the residue.

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