here on TinBoats, we like to see photos of issues so that accurate feedback can be provided.
Rkt - I second Dale's suggestion.
to answer your basic question: sand, scratch, pull or whatever to get ALL the existing
corossion removed and neutralized - then, apply fiberglass cloth and epoxy in place. (available at your auto parts store).
I would not suggest Polyester Fiberglass Resin for this job. E-P-O-X-Y only.
Raka Epoxy is a mail-order product and worth the money. https://raka.com/epoxy.html
this is something that you need to research on line to see what will work in your case.
Personally, I would recommend the West System
G/Flex 650 epoxy to seal the seams. Available at several online sources.
https://www.amazon.com/NRS-flex-Epoxy-2-4oz/dp/B002IZFPQE/ref=sr_1_cc_1?s=aps&ie=UTF8&qid=1481908617&sr=1-1-catcorr&keywords=G-Flex+650
it is a little expensive. There are several good videos on YouTube. A little goes a long way once warmed up.
I ordered two kits from Amazon @ $28.00 for two 4oz bottle kits - mixed one to one.
The project I am working on is quite extensive - and I want to do it right the first (and only) time.
I will use the G/Flex epoxy on the outside of the hull, then when flipped over and ready for paint,
I will use the Gluvit to seal the inside of the seams - then prime and paint.
Liquid epoxy would be the best fix. Just depends on your budget and how many times you want to fix it.
https://www.youtube.com/watch?v=UCOziXeTXzY
Please avoid caulks and especially anything that contains 100% pure silicone.
two-part epoxy putty is a band aid - it does not seap into the seams, cracks and crevices.
do it wrong and you open the door to possible future crevice corrosion issues.
Never-Ever use those "spray seal" products on boats as seen on TV !!!!!!!!!!!!!!!!
good stuff is expensive - bad stuff is cheap
jus my Dos Centavos
.