On 28 July, 16:01, Jeweller wrote:

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

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.