Soldering zinc

[Jeweller]

I'm expecting to need to alter some zinc downpipes and bends. These are new items with a finish (?) on them. Is lead solder going to be the route I should take?

Otherwise, advice please.

[John Rumm]

You will need an aggressive flux like bakers fluid for zinc, and a big enough gas powered "iron". Usually paint the flux on, and it quickly colours the metal black. Follow with bar solder and the iron - the solder should flow nicely to where the flux has been applied.

[Jeweller]

Does this mean a torch with a needle flame and the solder with a flux core are not up to the job?

[John Rumm]

Flux cored solder probably won't work for this, its better done with flux applied first when cold - otherwise in the time taken to get it hot enough to solder, the zinc surface will form a layer of oxide that prevents the solder flowing.

You may be able to use a fine flame - but a torch end with an actual soldering bit will make it easier as you can run it up and down the seams to get a neat fillet of solder. e.g.

[Jeweller]

Got it, thanks.

[Andy Dingley]

No! You need an iron, in particular you need a big (i.e. literally massive) warm iron, not a small hot flame. Zinc will react badly to high temperatures, even at a pinpoint, by even burning to powdery white zinc oxide, or even vapourising completely (zinc has a very low boiling point).

In practical terms, zinc is joined by mechanical rolling and crimping, rather than by soldering. It can be soldered (and for French cafe tables, it was) but it's a bugger of a process, particularly when outdoors.

[Jeweller]

Much obliged.

[NT]

Surely epoxy would be easier

NT

[Spamlet]

Now you are making us all jealous! Did you have to buy all those bikes to get the tyre designs for your rings (Which look pretty clever by the way)?

:-) S

[Matty F]

I am delighted with the solder pot that I made:

seems to tin almost anything that I can fit in it. You'd need a larger version.

[Dave Plowman (News)]

I made a new zinc tray for the top of a bay window which has a recessed flat roof ages ago and don't remember having problems soldering the seams to make it watertight. I used a Camping Gaz blowlamp which has a solder bit attachment rather than direct heat. Ordinary engineer's solder and Bakers fluid. Don't remember it being any more difficult than soldering other large sheet materials like tinplate.

[Jeweller]

Heh. Not the bikes but our garage is ram jam full of tyres. This prototyping is a seriously expensive business.

[Andy Wade]

Acid-cored solder might do the job, if you can still get it. (Wash the workpiece afterwards, as with any aggressive flux.)

[Frank Erskine]

Yes, you can - even from B&Q :-)

[John Rumm]

A separate paint-on-able flux makes a neater job on this sort of application I find...

[Frank Erskine]

True - that's what I use.