How to Solder a Copper Pipe Joint — Trade Method
Soldered copper joints last 60+ years — no push-fit competitor comes close. The trade calls this 'sweating' a joint. Here is the reliable method.
Step-by-step method
1. Cut and deburr pipe
Use a pipe slicer for a square cut. Ream the inside edge with a deburrer — a lip inside restricts flow.
2. Clean the mating surfaces
Wire wool or emery cloth to bright copper on the pipe end (25mm depth) and inside the fitting. Any oxide = weak joint.
3. Flux both surfaces
Thin coat of self-cleaning water-soluble flux (Fernox Powerflow or La-Co). Assemble the joint fully home.
4. Heat and apply solder
Play the blowtorch flame around the fitting (not directly on solder). When flux boils and hisses, touch solder wire to the joint mouth — it will draw in by capillary action.
5. Wipe and cool
Wipe excess solder with a damp cloth. Do NOT quench with water — let it air cool 30 seconds. Pressure test before boxing in.
Frequently asked questions
Yorkshire (solder-ring) vs end-feed?+
Yorkshire is easier — solder is pre-loaded, harder to under-solder. End-feed is cheaper and marginally stronger if done right. Trade preference: Yorkshire for domestic, end-feed for commercial.
What solder is safe for drinking water?+
Lead-free plumbing solder only (marked BS EN 29453). Never use electrical solder — it contains lead and is illegal for potable water.