How they differ
Solid wire relies entirely on an external shielding gas to keep atmosphere out of the weld pool. Flux-cored wire carries flux inside a tubular wire; depending on the type it either generates its own shielding as the flux burns, or supplements a gas shield and adds slag control on top of it.
That single difference cascades into everything else: wind tolerance, out-of-position behaviour, deposition rate, cleanup and cost.
Where solid wire wins
- Indoor and sheltered work where a gas shield stays where you put it.
- Thin material and appearance-critical welds — less spatter, no slag to chip.
- High-volume repetitive fabrication with consistent, prepared material.
- Lower consumable cost per kilo of wire.
Where flux-cored wins
- Outdoor and site work where wind would strip a gas shield.
- Out-of-position welding — vertical and overhead — where slag supports the pool.
- Thicker sections and higher deposition rates, so fewer passes.
- Less-than-clean or as-received material.
The cost that gets missed
Comparing price per kilo of wire is the wrong comparison. What matters is cost per kilo of deposited weld metal, which includes deposition rate, duty cycle, gas consumption and the labour spent chipping slag or grinding spatter.
Flux-cored wire usually costs more per kilo and can still be cheaper per finished joint on heavy site work, because it lays metal faster and needs no gas. Solid wire is usually cheaper per finished joint in a workshop, because nothing has to be cleaned off afterwards.
What most operations actually do
Carry both. A workshop with a site crew runs solid wire on the bench and flux-cored in the bakkie, and the store holds the fast-moving diameters of each. It is not indecision — it is matching the consumable to two genuinely different jobs.