Folkboat Hull (grp sheathed) painting

[woolleyhatter]

dear fonts of all knowledge
I have a lovely FB which i discovered recently is sheathed on the topsides to just below the waterline. I'd like to re-paint her (prob white which is her current colour), and i'm at odds how to "prepare" the existing hull. It's in reasonable condition but it's easy to see the imperfections.
My question is how do i go about getting it prepared?. Do i rub down the gelcoat (which has been painted on by hand), or do i go with sandpaper/wet and dry, and then prime and paint etc, or should i take it right down to the bare glass and go from there.
Boat is undercover and in a huge shed and temp etc is good.
Any advice will be well received and recommendation on paints etc would be great.
Many thanks

 

[sailorman]

http://www.international-marine.com/Paint Guides/MPG_PaintApplication.pdf

 

[oldharry]

Shuddering at the thought of a FB hull 'sheathed in GRP'.

I would immediately ask myself several questions: Why on earth do that? What has it been sheathed with? Polyester resin does not stick well to timber, and falls off again very easily. What is going on underneath? If it was done with polyester resin and the bond is failing, that provides ideal conditions for rot.

If on the other hand it has been done 'properly' using a proven sheathing system like the West system or even Cascover then there should be nothing to worry about. But your description sounds more than a bit suspect that it has been botched. But even so - a carvel hull, designed to flex and move, with a 'hard' sheath? Doesnt sound good to me.

 

[laurance]

Old Harry raises a valid point, however if you are satisfied nothing untoward is going on under the sheathing you can simply abrade the flow coat till you have flatted out the brush marks, finishing with say 120 grit to leave a good key, then give the surface a really thorough wash n' rinse and follow with your chosen paint system: marine enamel or one part polyester, or, my favourite, a good quality trade oil gloss and undercoat such as Dulux's Weathershield. No special primer needed in an case.
In theory, if you are sure the sheathing is sound you could use a two-part polyester but you are probably going to add to the problems Old Harry has alluded too should they arise. I can think of one instance I know of with a sheathed carvel hull two-packed that has lasted for years without issues, but this is on a very stable well built hull. Two pack is unpleasant to work with and expensive, hardly worth the time and effort on a Folkie' that you can get round in a morning with paint ordinaire every couple of seasons. Besides you can't go cheating on the sombre duty wooden boat maintenance, that wouldn't be fair on the rest of us.

 

[laurance]

....further, assuming she is a clinker Folkie' she may have been glassed-up as a way of saving a beat up hull otherwise needing a rebuild, so I would only want to know what was under the glass if I was prepared for the worst. Otherwise slap some paint on and get sailing until you really have to have a look.
If a carvel Folkie' and especially with splined seams, as in one case I know, a sound layer of sheathing may be less to worry about....