Which Solder Should You Use for Plumbing, Electrical, and Stained Glass Work?

Summary

Solder is a fusible alloy used to join metals by melting it at a lower temperature than the workpieces and allowing it to flow into the joint by capillary action. The correct solder selection depends on the application: potable water plumbing, gas, electrical, electronics, stained glass, or leadwork each have different requirements for alloy composition, melting temperature, flux type, and regulatory compliance.

The most significant regulatory boundary in UK practice is the prohibition of lead in potable water plumbing. Lead is a cumulative neurotoxin and the Water Supply (Water Fittings) Regulations 1999 prohibit the use of any fittings or materials (including solder) that would cause water to become unwholesome. WRAS (Water Regulations Advisory Scheme) approval is the standard mark of compliance for plumbing solder.

For electrical work, the EU RoHS Directive (Restriction of Hazardous Substances) has prohibited lead in new electrical and electronic equipment since 2006. This means standard 60/40 lead-tin solder cannot be used in new electronic equipment, though it is still used in repair work on pre-2006 equipment.

Key Facts

• Water Supply (Water Fittings) Regulations 1999 — UK regulation prohibiting materials that make water unwholesome; lead solder in potable water systems is prohibited
• WRAS (Water Regulations Advisory Scheme) approval — The standard accreditation for plumbing materials used with drinking water; look for WRAS-approved lead-free solder for all domestic plumbing
• Lead-free plumbing solder — Typically 97% tin / 3% copper (Sn97Cu3) or tin-silver-copper (SAC) alloys; melting range approximately 230–250°C (higher than 60/40 lead-tin at 183–190°C)
• 50/50 lead-tin solder — Traditional "plumber's solder"; 50% lead, 50% tin; melting range 183–215°C (wide pasty range, useful for wiped joints); now illegal for potable water in UK; still used for lead weatherings, flashings, and non-potable applications
• 60/40 tin-lead electrical solder — 60% tin, 40% lead; melting point approximately 183°C (eutectic-near); traditionally standard for electronics; restricted under RoHS for new equipment
• Lead-free electrical solder — Typically SAC 305 (Sn96.5/Ag3/Cu0.5), or SN100C (Sn+0.7Cu+0.05Ni) for wave soldering; higher melting point (~217–220°C) than lead-tin; requires hotter iron and different technique
• BS EN 29454 (ISO 9454) — Classification standard for flux for soft soldering; defines categories 1 (rosin-based), 2 (organic), and 3 (inorganic — acid); important for flux compatibility and residue cleaning
• Plumbing flux must be non-aggressive — Use only flux approved for copper plumbing; aggressive (acid) flux corrodes copper pipe and fittings; the Plumbing Flux standard in the UK is fluxes approved for use under BS EN 29454 category 1 or 2, with no chlorides
• Stained glass solder — Typically 50/50 or 60/40 lead-tin; lead content is acceptable here as the joints are not in contact with food or water; the joints are decorative and structural (holding leaded glass panels)
• Wiped joint (lead pipe) — A traditional plumbing technique using 50/50 or 53/47 lead-tin solder; applied by a moleskin pad (wiped joint); now largely obsolete for new work but relevant to restoration of original lead plumbing in historic buildings
• Soldering temperature — Lead-free plumbing solder requires higher iron/torch temperatures; 95/5 (tin-antimony) and 97/3 (tin-copper) alloys require a slightly hotter flame; if the solder does not flow freely, the joint is not hot enough — not that more flux is needed
• Potable water system requirement — Not just solder but all fittings, fluxes, and jointing compounds used in potable water systems must meet the Regulations and ideally be WRAS-approved
• Gas systems — Solder joints on gas pipework require a high-temperature solder; capillary fittings for gas use integral solder rings; check the manufacturer's specification and confirm the solder used is appropriate for gas service temperatures and pressures

Quick Reference Table

Detailed Guidance

Potable Water Plumbing — Lead-Free Requirement

The Water Supply (Water Fittings) Regulations 1999 (England and Wales; equivalents in Scotland and Northern Ireland) require that no fitting, pipe, or jointing material contaminates the water supply. Lead solder dissolves into water — particularly soft, acidic water — and was a significant source of lead ingestion in UK domestic properties before the prohibition.

All plumbing solder used in domestic water systems must now be lead-free. The WRAS product approval process provides a clear list of approved solders — check the WRAS product approval directory at wras.co.uk before specifying. The most common UK plumbing solder is 97/3 (tin-copper) or a tin-silver-copper alloy.

Flux selection: The flux used with lead-free solder for copper plumbing must also be WRAS-approved (or specifically formulated for potable water use) and must be non-aggressive. Do not use electrical acid-based flux on copper plumbing — it corrodes the copper over time and the chloride residue contaminates the water. Use a specialist plumbing flux (Yorkshire Flux, Frys Powerflow, or equivalent) rated for copper plumbing.

Higher melting point: Lead-free plumbing solder has a higher melting point (approximately 230–250°C) than lead-tin solder (183°C). This means the joint must be heated more thoroughly with the torch before the solder flows. A common error when switching from lead to lead-free solder is to apply the solder too early — if the joint is not hot enough, the solder will ball up on the surface rather than flowing into the joint. Heat the fitting first (not the solder), and apply solder when the fitting is hot enough to melt it on contact.

Electrical Soldering — RoHS and Lead-Free

The RoHS Directive (Restriction of Hazardous Substances in Electrical and Electronic Equipment) has been part of UK law since 2006 (implemented as the Electrical and Electronic Equipment (Restriction of the Use of Certain Hazardous Substances) Regulations, now retained UK law post-Brexit). It prohibits lead in new electrical and electronic equipment.

In practice, this means:

• New circuit boards, electronic components, and consumer electronics must use lead-free solder (typically SAC305 or similar)
• Repair work on pre-2006 equipment may use either lead-tin or lead-free solder; lead-tin is often preferred for repairs because it is more forgiving and has a lower melting point

Lead-free solder for electronics requires a hotter soldering iron (typically 350–380°C tip temperature vs 300–330°C for lead-tin) and has slightly different working properties — it tends to look duller when cooled (a dull joint with lead-free solder is not necessarily a dry joint as it would be with lead-tin).

Flux for electrical work: Use rosin-based flux (category 1 under BS EN 29454) — either RMA (rosin mildly activated) or RA (rosin activated). Do not use water-based or acid flux (category 3) for electrical/electronic work — the ionic residues are conductive and cause corrosion and short-circuit failures.

Stained Glass and Decorative Leadwork

Traditional leaded glass (stained glass windows, leaded lights) uses lead came — H-section extruded lead strip — to hold glass pieces in a panel. The joints between lead came pieces are soldered. For this application:

• 50/50 lead-tin solder is traditional and remains in use (the joint is not in contact with food or water)
• The solder joint is a structural connection holding the lead came together at intersections
• Tallow or light rosin flux is used; the flux is washed off after soldering with a proprietary came cleaner

The high lead content of 50/50 solder creates a larger pasty range (the temperature range between fully liquid and fully solid) than eutectic alloys. This wide pasty range was historically useful for wiped plumbing joints (lead-tin solder can be shaped with a pad while in the pasty state). For stained glass, it is workable with a standard soldering iron.

COSHH considerations for lead soldering: lead fume is a significant hazard. Adequate ventilation (LEV or open-air working) is required for any lead soldering work. Wash hands thoroughly before eating or leaving work.

Gas Systems

Capillary solder fittings for gas (copper and copper-alloy) are available with integral solder rings. The solder specified for gas capillary fittings is not the same as standard plumbing solder — gas fittings are pressure-rated and tested, and the solder must achieve the required mechanical strength and gas-tightness. Always use the fitting manufacturer's specified solder or integral solder ring fittings rather than trying to add solder separately. Confirm compliance with BS 7291 (thermoplastic) or BS EN 1254 (copper fittings) as relevant.

For gas installations, any soldered joint must be tested for gas-tightness before the system is commissioned. Follow Gas Safe Register guidance for all gas pipework installation.

Frequently Asked Questions

Is 50/50 solder still legal for use in heating systems (not drinking water)?

Technically, the Water Supply (Water Fittings) Regulations 1999 apply to water supply systems for drinking water. Closed-loop heating systems (central heating circuits) are not subject to the same prohibition on lead. However, best practice (and many specifiers) now requires lead-free solder throughout to avoid confusion about which system is which, and to reduce lead exposure to installers and future occupants. Lead-free solder for heating systems is strongly recommended.

Why does my lead-free solder look dull instead of shiny?

Dull appearance is a normal characteristic of many lead-free solder alloys — it does not indicate a "dry joint" (a cold joint with poor adhesion) as it often would with lead-tin solder. A dry joint with lead-free solder usually shows as a rough, grainy, or lumpy texture rather than simply being dull. The key test is whether the solder flowed into the joint cleanly when the joint was at the correct temperature.

Can I use plumbing flux for electrical soldering?

No. Plumbing flux (even non-aggressive plumbing grade) is not appropriate for electrical connections. It may contain chlorides or other ionic substances that cause corrosion on circuit boards and wire connections over time. Use rosin-based flux (category 1, BS EN 29454) for all electrical work.

What flux should I use for lead-free solder on copper pipe?

Use a WRAS-approved non-aggressive plumbing flux specifically formulated for use with lead-free solder. Products such as Frys Powerflow, Yorkshire Flux, and Harris Stay-Brite Flux are common examples. Always check that the flux is compatible with lead-free solder — some older plumbing fluxes were optimised for 50/50 lead-tin and may not perform as well with lead-free alloys.

Do I need WRAS approval for solder used on a commercial building water supply?

Yes. The Water Supply (Water Fittings) Regulations apply to all water supply systems in England and Wales, domestic and commercial. All materials in contact with drinking water should meet the requirements and are ideally WRAS-approved. Building regulations inspectors and water companies can require evidence of compliance on commercial projects.

Regulations & Standards

• Water Supply (Water Fittings) Regulations 1999 (SI 1999/1148) — Prohibition of materials (including lead solder) that contaminate drinking water

• The Electrical and Electronic Equipment (Restriction of the Use of Certain Hazardous Substances) Regulations 2012 (UK RoHS) — Prohibition of lead in new electrical and electronic equipment

• BS EN 29454 (ISO 9454) — Specification for fluxes for soft soldering; classification and requirements by activity and residue type

• WRAS (Water Regulations Advisory Scheme) — Product approval scheme for materials used in contact with drinking water

• Gas Safety (Installation and Use) Regulations 1998 — General duty for gas installation work to be carried out safely; relevant to solder used in gas pipework

• WRAS Product Approval Directory — Search for approved solders and fluxes for potable water use

• Harris Products — Lead-free solder technical data — Alloy composition and melting ranges for plumbing solders

• HSE — Lead: control of exposure in the workplace — COSHH requirements for lead solder and flux work

• IPC J-STD-006 — Industry standard for electronic solder alloy specifications (referenced for SAC alloys)

• Gas Safe Register — Technical guidance — Installation requirements for gas pipework including jointing methods

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