I'm doing my 2nd refit
on my steel girl as well. In 2003 I debated some of the same questions concerning the epoxy coated interior. I suspected the coating had been applied during a 1993 major refit
and internal redesign but had never been painted nicely in open area's not covered by insulation
& wood. I used a rust guard acid treatment on all areas I found. Then used a pointed welding hammer and steel brush to pop away any affected areas. There are epoxy steel filler products that adhere & harden nicely but I personally prefer the old fashion way of weld filling, grinding back then treating small pits. I cleaned, lightly sanded, cleaned again with acetone then used a 2 pack enamel primer. Sanded lightly (again the acetone) then 2 coats white 2 pack enamel paint. Sounds like overkill but the older epoxy coating (I suspect was blown on) wasn't smooth and I was looking for a smooth, easy to wipe down clean surface. My theory is; the easier you can make a surface to clean, the less likely it is to hold any surface substrates that might cause corrosion
. The 2 pack is a challenge both inside and out with necessary respirator, ventilation... but I've found the advantage to a hardener bound enamel paint to be valuable long term.
On the Bilge / Keel
area; If you find a minor weathering crack in the concrete, I wouldn't give it much worry. But, if you see obvious areas where water
has been allowed into or around larger cracks or the sealed keel
area appears to have been violated by moisture that might have crept into the sealed area. My preference here again is both 2 pack primer then 2 pack paint for a reliable seal. Concrete floor paints are fine in a garage but the marine
demands bend the rules greatly.
I would (and have) drilled a small (plastic straw size) hole in the lowest keel area from the outside. If you strike water, just let it drain nicely. I left it open a few days, made sure I used a straw to keep the hole clear then closed with a weld. I didn't get more than about 20 seconds of water but the good feeling of knowing I've cleared it out and resealed it solid has lasted me 12 years!
I hope some of this is useful ~ Best wishes & fair winds.