cast iron rust prime or leave it?

Remove anything flaking or near to flaking first, then paint should be fine for garden quality jobs

Rust carries on rusting in my experience and cracks the paint more moisture gets in etc. However how long do you want it to last, probably outlast most of us even if it does need the odd clean and touch up. More 'rustic' as they say! Brian

You could use phosphoric acid, leave for say 6 hours and then wash off before painting.

Phosphoric acid (rust remover/converter) available on Ebay in various quaities

HCl is far quicker. Watch the fumes.

NT

True of rust on car panels, less of an issue on (single pieces of) cast iron IMHO.

Wire brush and gloss paint will work; wire brush, phosphate or zinc primer will last longer.

yes, but ferric chride is soluble, aqnd just washes off. Iron phosphate however stays in te iron and acts as a protective layter and a sort of primer

but looks like it is not that bothered by it. Will oil based u/c then gloss work or do I need to use rust inhibitor primer first? Have some but would save time if the paint alone will be enough.

Thanks all. The chemicals sound a bit scary - was just wondering whether pr imer needed. Being a bit rustic myself going to crack straight on with u/c. Sure it will all work out in the end.