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Prep for bottom paint

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JanS48
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USA
141 Posts

Initially Posted - 04/16/2015 : 00:29:34

Greetings all
What is the minimum prep before painting the bottom? The bottom has been washed clean. Is sanding a must? If so is a light 'scuffing' all that is needed?

82 C25 FK Std Rig

Thanks in advance
Jan

82 C25 SR FK
Sailing out of Newport Harbor.

dasreboot
Admiral

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803 Posts

Response Posted - 04/16/2015 : 03:43:57

what kind of paint? paints that build up, you can scuff until the build up is too thick, then you have to sand it off. vc17 adheres to the last coat with no sanding requires.

Todd Lewis
Eowyn 87 TR/WK C25 #5656
ARWEN 84 TR/SK C25 #4031
www.mainsailsailingschool.com

Stinkpotter
Master Marine Consultant

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Djibouti
9013 Posts

Response Posted - 04/16/2015 : 06:05:06

I find ablative (or "copolymer") paints don't need sanding--it just reduces their longevity by removing part of what normally sluffs off. Light sanding is generally recommended for hard paint. Hard can't go on top of ablative, but ablative can go on hard, subject to the compatibility listed on the manufacturer's site. Incompatibility suggests that the underlying paint will peel and flake off--probably right on your roller. The new water-based paints seem to be less prone to causing that because they don't contain the hydrocarbon solvents that soften other paints.

Now I've told you more than I know...

Dave Bristle
Association "Port Captain" for Mystic/Stonington CT
PO of 1985 C-25 SR/FK #5032 Passage, USCG "sixpack" (expired),
Now on Eastern 27 $+!nkp*+ Sarge

Voyager
Master Marine Consultant

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5231 Posts

Response Posted - 04/16/2015 : 16:35:47

With ablative, the surface seems to dry out over the winter so seem to develop a dusty coating that I prefer to roughen up. As well, there are areas that flake off easily, so I go around and scrape those down to the undercoat. At that point I wash the bottom, let it dry then apply a slightly thinned ablative paint using a short nap roller.
Seems to work out well.
After several years' paint, I find it best to scrape or heavily sand to smooth out the rough spots. Sometimes I get down to the barrier coat so I start the cycle all over again.

Bruce Ross
Passage ~ SR-FK ~ C25 #5032

Port Captain � Milford, CT

islander
Master Marine Consultant

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3992 Posts

Response Posted - 04/16/2015 : 16:50:43

quote:
With ablative, the surface seems to dry out over the winter so seem to develop a dusty coating

It's a bit of a shock in the spring to see that and thought for sure I needed a full paint job but a quick once over with a dry soft brush on a stick takes that dusty coating off. After that I sanded a few rough spots and touched them up. Good to go for the 3rd season. I'll save the full redo for next year. At $700 per paint job I got to get some mileage

Scott-"IMPULSE"87'C25/SR/WK/Din.#5688
Sailing out of Glen Cove,L.I Sound

Steve Milby
Past Commodore

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5851 Posts

Response Posted - 04/16/2015 : 16:52:02

Like Bruce, I don't paint over that dusty surface that you sometimes get with ablative paints. I wash the bottom with clear water and either a sponge or a plastic scrubber, and then paint over it. I think that dusty stuff is probably a combination of dirt and perhaps some paint residue that sloughs off while the boat is on the hard, and it doesn't require much effort to get it off.

Steve Milby J/24 "Captiva Wind"
previously C&C 35, Cal 25, C25 TR/FK, C22
Past Commodore

Edited by - Steve Milby on 04/16/2015 17:01:57

Stinkpotter
Master Marine Consultant

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Djibouti
9013 Posts

Response Posted - 04/16/2015 : 20:32:28

One more consideration: If the paint is ablative and there's an adequate amout already there, maybe you don't want to add more. The best way to determine the "adequate" part is by having a contrasting ablative "signal coat" under your chosen color that, if visible in some areas, signals that it's time to add some more paint in those areas. Adding a full coat of ablative paint to most sailboats every year is just building up a thick, heavy layer that might develop performance-robbing craters, but isn't really adding to fouling protection. You might be surprised by how little sluffs off in a season, except maybe on the fronts of the keel and rudder.

Dave Bristle
Association "Port Captain" for Mystic/Stonington CT
PO of 1985 C-25 SR/FK #5032 Passage, USCG "sixpack" (expired),
Now on Eastern 27 $+!nkp*+ Sarge

Edited by - Stinkpotter on 04/16/2015 20:45:17

JanS48
Navigator

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USA
141 Posts

Response Posted - 04/17/2015 : 00:31:18

Thanks all for the replies, it is an ablative paint, the bottom isn't so bad, I'm just scraping/sanding the loose stuff off, the keel however is another matter, parts are a 1/16 thick or more and on many spots just touching it with a scraper takes it down to the glass. What I'm currently doing there is to scrap til I get solid. Does this sound reasonable? When I get to bare glass on the keel do I need to prep that with anything first? By the looks of this and others in the boat yard it seems to be commonplace. Also when I look at the keel glass it appears to have a 'crazed' pattern with some rust color but the glass is solid from what I can tell. Is this normal?

Thanks in advance
Jan

82 C25 SR FK
Sailing out of Newport Harbor.

Stinkpotter
Master Marine Consultant

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Djibouti
9013 Posts

Response Posted - 04/17/2015 : 07:01:50

I'll defer to anyone else with an '82 fin keel, but I believe that year the fin was still painted cast iron--no fiberglass encapsulation. Some time around '83, I think,

it changed to fiberglass-encapsulated lead. (The glass is quite thick because the lead is more dense--apparently to keep the shape the same.) If yours is iron and there's fiberglass below the keel-hull joint (something like 10" below the bottom of the boat), the glass was probably added by an owner in an attempt to prevent the rust. Otherwise, what's more normal is just many layers of hard paint (ablative wasn't in common use then), and hard paint loses its antifouling effectiveness when exposed to air.

As it eventually starts letting go, things get ugly (as you're seeing)--sorta like the face of the moon. In any case, the iron (if that's what the '82 has) always weeps some rusty water through the mess--on every one I've seen in boatyards. But not to fear--there's plenty of iron in there! (My '85 was encapuslated lead.)

If you get down to the iron (assuming that's what it is), I would scrape and wire-brush the loose rust, prime it with some "rust reformer" (an acid-based coating that turns the iron black), sand lightly, and put a couple of coats of the ablative paint over it.

Dave Bristle
Association "Port Captain" for Mystic/Stonington CT
PO of 1985 C-25 SR/FK #5032 Passage, USCG "sixpack" (expired),
Now on Eastern 27 $+!nkp*+ Sarge

Edited by - Stinkpotter on 04/17/2015 07:13:29

wanderer13
1st Mate

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Response Posted - 04/17/2015 : 07:15:13

I have a 1981 iron fin keel and it is encapsulated in fiberglass.

Steve Milby
Past Commodore

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5851 Posts

Response Posted - 04/17/2015 : 07:47:41

quote:
Originally posted by wanderer13

I have a 1981 iron fin keel and it is encapsulated in fiberglass.

Mine was also a 1981 boat, and the cast iron keel was faired with epoxy compound, but it was not "encapsulated". The cast iron keel was a crude casting, and it had to be smoothed with epoxy compound. The depressions on the keel were filled with epoxy, but the high parts were bare iron, with a factory applied coating of (I think) coal tar epoxy, to seal out the moisture. An encapsulated keel is different. The lead ballast is completely encased in 2-3 layers of fiberglass roving. It's possible that an owner might have laid layers of fiberglass cloth over a 1981 cast iron keel, but I never saw or heard of one coming from the factory that way.

Steve Milby J/24 "Captiva Wind"
previously C&C 35, Cal 25, C25 TR/FK, C22
Past Commodore

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