Bottom Paint Question Part 2

[bffatcat]

Unfortunately my first post was not articulate enough. I said the bottom was down to the bare fiberglass on my first post, my error. I should have said down to bare jell coat in spots

I dont know what bottom paint was used when the boat was new in 1975
but I do know it was a hard bottom paint. Again when I got the boat 9 years ago it had an old blue caked and chipped hard finish bottom paint on it. There was never any barrier coat applied to the bare bottom. When the boat was new the bottom was first painted with the hard bottom paint right on top of the jell coat When I first got the boat I sanded the old hard bottom paint smooth. The entire bottom was covered with this old blue hard paint. It was smooth with good adherence after sanding no bare spots. I would have had to strip the bottom to get the old paint off so I painted over the old blue paint with 2 coats of red ablative bottom paint. and have continued to do the same each spring for the last 8 years. When I had the bottom pressure washed each fall some of the red ablative paint came off, but the original blue hard finish paint always stayed in tact. This year was different. When the bottom was pressure washed several large sections of the old hard blue paint came off exposing the bare jell coat. My Question: for someone in the know. Can I sand the bare jell coat apply 2 coats of ablative directly on top of the bare spots or do I have to put some kind of protective coating on the bare jell coat before applying the ablative bottom paint. The bare spots are about 10% of the entire bottom

 

[Tim R.]

Because you are thinning areas of gelcoat, I would build up the bottom with an epoxy barrier coat like Interluxes 2000. Next apply a contrasting color multi season ablative to act as a signal coat so you know when to repaint, then apply 2 coats of your finish ablative. I have done this on 3 boats now including my ericson 35.

 

[CalebD]

Articulate enough.

Unfortunately my first post was not articulate enough.

My Question: for someone in the know. Can I sand the bare jell coat apply 2 coats of ablative directly on top of the bare spots or do I have to put some kind of protective coating on the bare jell coat before applying the ablative bottom paint. The bare spots are about 10% of the entire bottom

While Tim's recommendation is probably the most proactive approach to treating your hull and what I would like to do sometime to my 1967, 41 year old boat but given the amount of paint that is under the ablative layers I keep applying I am not looking forward to the task, or the number of days it would take me to do it.
In order to get the best results with a barrier coat it is my understanding that you would want to get ALL the old paint off and then apply the barrier coats, then re-coat with anti-fouling paint several times.
To answer your question though, you can put bottom paint right on top of gel coat (IMHO). If there is bare gel coat showing why do you want to sand it? It should be pretty smooth to begin with. I would use the finest grit sandpaper you can get your hands on for this so as not to thin the coating. You could always just rub it with acetone to see what that does. I always like to wipe the hull down with something nasty like Interlux #202 thinner before re-painting to get all foreign stuff and wax off for best adhesion.
If I were in your shoes I would continue to do what you have been doing until more or all of the older hard paint falls off as that would be the time to consider doing a barrier coat job unless you want to be real proactive like Tim and Mainesail. If your boat gets hauled out for a good part of the year and you are not getting blisters then a barrier coat job is still probably a good idea, just not imperative right now.
Advice is cheap and the above are only my opinions