I've been advised to clean off the rust and old paint and repaint with
hammerite type paint. Just how much rust will hammerite tolerate?
I'm using a abrasive disc on a 115mm grinder, and its taking off the
paint and surface rust fine but the surface is somewhat uneven and
there's rust in the pits. Do I need to treat for these rust areas?
The bath is outside upsidedown so access is as good as it can be.

Rob