We get brown algae stains at the waterline and last couple years I used heavy polishes, an orbital sander with fine grit, and other stuff, so I'm pretty sure I put
"etching" into the gelcoat, as well as scrubbing many layers off. SO now I use muratic acid & water mix to clean without sanding/polishes, BUT what now to do
to the scarred surface of the gelcoat ? How we know when its time to put new gelcoat or a 2 part paint over it ?
Here goes a foolish thing, which is an attempt to summarize countless years of posts on this subject by several generations of members:
The time to paint your hull is when you want it to be a different color.
All other gelcoat flaws are fixable, often with amazing results. Personally, I love a dark colored hull, so I bought Don Casey's book on sailboat refinishing (very cheap on Amazon, under $10) and followed his advice to the letter using two part polyurethane paint. He is a god, n my humble opinion.
Wes
I'll add something to what Wes said. The time to paint is when you are tired of the maintenance required to keep your old gelcoat looking decent. You can generally make old gelcoat look good, but it takes more maintenance than I want to do to keep it looking good all the time. When you recoat with catalyzed polyurethane, maintenance goes down to about an hour a year on a 23 hull, wash and high quality wax.
Catalyzed Polyurethane not re-gelcoat. It is tougher and more UV resistant than gelcoat.