On Nov 22, 9:42*pm, Adrian wrote:
Both of those require REALLY clean - freshly blasted
steel to give of their best.

Indeed, freshly blasted is Sa2, bright mirror is Sa2.5.

You can get Sa2.5 on lightly corroded auto steel with a 3M clean-n-
strip.
An example would be a scrape which has been neglected such that paint
has domed and gone brittle in the surrounding area, underneath you
will find dark millscale which the 3M Clean-n-Strip cleans out to
leave bright shiny metal as a broad crater of limited depth. Then
either zinc product works superbly at stopping corrosion dead - but
are mechanically weak. You need galvanising primer, then normal car
paint, but it is still a weak underlying area.

For this job, they recommended
Rustoleum 769 primer.

Good and that tackles the weakness of pure zinc products (they are
meant for freshly drilled or ground welds on RSJ, where you want the
longest life but also where abrasion resistance is immaterial).

You can buy miniature sand blasting kits; exactly like a paint air
sprayer, plug in to a compressor, will blast small areas for auto
repair etc. Add-ons for pressure washers also exist of course.