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Catalina/Capri 25/250 Sailor's Forums

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below waterline hull prep

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tbosch
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163 Posts

Initially Posted - 11/23/2008 : 10:53:39

Removing the bottom paint from my '80 Cat 25 exposed many places where the gelcoat seems to have flaked off. There doesn't seem to be moisture or odor in these so I don't think they are blisters. What should I do with these? I could leave them as is and seal them, and the rest of hull below the water line, with multiple coats of unfilled epoxy. Or I could fair the hull by meticulously patching them all with filled epoxy. I'm sure there are some opinions out there. What do you think? Has anyone else dealt with this?

Todd
1980 C25 SR/FK "Dora"

Edited by - on

Steve Milby
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Response Posted - 11/23/2008 : 11:09:20

It's hard to say for sure what caused it. They don't look like blisters, which raise up in little bumps full of water, like a blister on your heel. They look more like the gelcoat is just becoming very thin, as a result of repeatedly sanding the bottom. If so, I don't think it's cause for serious concern. I'd wet-sand it by hand enough to smooth the surface, but don't overdo it. Then apply a barrier coat, carefully following the manufacturer's instructions, and then apply antifouling paint.

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Nautiduck
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Response Posted - 11/23/2008 : 11:11:01

Since the gelcoat does not provide a water barrier and your hull seems fine except for the flaking you could simply put some anti-fouling paint on and go sailing.

How did you remove the paint? Could that process have resulted in the flakes??

Update: Now I remember that you had the bottom soda-blasted. Maybe there were some hard particles in the soda supply??

Edited by - Nautiduck on 11/23/2008 11:13:32

tbosch
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Response Posted - 11/23/2008 : 12:10:01

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Nautiduck
 
How did you remove the paint? Could that process have resulted in the flakes??

Update: Now I remember that you had the bottom soda-blasted. Maybe there were some hard particles in the soda supply??
<hr height="1" noshade id="quote"></blockquote id="quote">

I did have it soda blasted (dry method). I assumed that the flakes that came off were loose to begin with and it's just as well that they came off during the process. But I suppose that it could be collateral damage. I don't know enough about the process to know what the side affects could be.

I'm glad to hear the feedback so far! Filling all of those flakes doesn't sound like fun.

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OLarryR
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Response Posted - 11/23/2008 : 17:14:30

If these areas were the result of soda blasting, I would recommend not going that route again for fear of uncovering addl areas. I guess it could be considered good that you now are aware of the thin areas but as long as they right now are just a cosmetic issue, I would try to avoid more speckled areas. If they or you pressure wash it at the end of the season, can't you then just lightly sand the old bottom paint and then apply a new coat over it and forgo the soda blasting ?

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Steve Blackburn
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Response Posted - 11/23/2008 : 17:29:11

For what it`s worth, when I removed my antifouling using a high presure washer some of these flakes did come off. Some bigger than others where some of the flakes were about the size of a quarter. I read on the subject and the suggest procedure was to remove about 1 mm off with a dremel (both in depth and width). Then use Acetone to clean them out real good. I followed by filling in with MarineTex and wet sanding. In my opinion my hull is better than new because I believe those were week areas to begin with.

Edited by - Steve Blackburn on 11/23/2008 17:29:56

tbosch
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Response Posted - 11/23/2008 : 19:52:17

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by OLarryR
 ... can't you then just lightly sand the old bottom paint and then apply a new coat over it and forgo the soda blasting ?
<hr height="1" noshade id="quote"></blockquote id="quote">

Absolutely! I only went the soda blasting route because the old bottom paint was very thick, in very bad shape, and the cast iron keel needed a lot of patching and fairing. I hope to never do this again!

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tbosch
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Response Posted - 11/23/2008 : 19:57:49

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Steve Blackburn
 ... the suggest procedure was to remove about 1 mm off with a dremel (both in depth and width). Then use Acetone to clean them out real good. I followed by filling in with MarineTex and wet sanding.
<hr height="1" noshade id="quote"></blockquote id="quote">
Steve,
I plan to fill any larger areas that I find the same way you did. So far I haven't seen any bigger than a pencil eraser. For the smaller ones, like in the picture, I think I will just settle for the barrier coat.

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Steve Blackburn
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Response Posted - 11/23/2008 : 20:33:53

Todd, why settle with just barrier coat? My concern was water osmosis through these tiny holes where water can inseep between the gelcoat and fiberglass below. Just dremel a little and apply MarineTex. It takes 20 minutes to do.

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Jefffriday
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198 Posts

Response Posted - 11/23/2008 : 20:52:01

If the whole bottom looks like the picture, you need all winter to repair each one, I'd go with the epoxy barrier coat program. That should easily seal it all up. This makes me wonder about the variables in the soda blasting process, are they all the same?

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Steve Milby
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5897 Posts

Response Posted - 11/24/2008 : 07:31:39

The remedy depends on the nature of the problem, and how you plan to use the boat. If the problem was caused by blisters, then you should follow Steve B's procedure, and grind out and fill the blisters before you barrier coat the boat. If you do this, you should grind out the blisters in the fall, and then let them dry out on the hard, during the winter, and then fill them and barrier coat the bottom in the spring. If the problem was caused by overly aggressive removal of old bottom paint, then you can just smooth the bottom a bit and barrier coat it. If you plan to race the boat seriously, then you might want to use a little filler to smooth the surface a bit before you barrier coat the bottom.

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Nautiduck
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3704 Posts

Response Posted - 11/24/2008 : 15:17:22

Gelcoat is not a waterproofing layer. Gelcoat is simply cosmetic and is used so that the criss-cross pattern of the fiberglass mat does not show through. If the fiberglass mat is properly done then there will be no intrusion of water into the hull even if all of the gelcoat is removed. I believe that if you had blistering you would see some blisters and the flaked holes would be weeping an acidic foul smelling liquid. For a good read about blisters check this guy out. He is the expert on blistering.

[url="http://www.yachtsurvey.com/blisters.htm"]David Pascoe[/url]

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John Russell
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Response Posted - 11/24/2008 : 16:14:44

Try this [url="http://www.sealakeyachts.com/service/blisters.html"]article for blister info[/url]. Plain english. Makes sense to me. No equivocation.

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Dave Bristle
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Djibouti
10005 Posts

Response Posted - 11/24/2008 : 17:31:59

I'm suspicious you had pin-head sized blisters, which are not uncommon in fresh water, and the blasting opened them up and then ripped off the loosened gelcoat, creating the irregular shapes. (That would probably also blow out the trapped water.) For a non-racer, I agree that some light sanding (to make sure all loose gelcoat is off) and barrier coat is sufficient. For a racer, I'd suggest going over it with Marine Tex on a wide putty knife for fairly fast coverage, then some sanding to smooth it, then the barrier coat.

Barrier coating is more important in fresh water than salt because fresh permeates more readily. Don't sand gelcoat if you're not barrier coating it--that makes it more permeable. If barrier coating, follow the directions religiously.

Edited by - Dave Bristle on 11/24/2008 17:42:18

Nautiduck
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Response Posted - 11/24/2008 : 19:18:20

John, good article. Both of these authors agree that blisters are not the big issue that we tend to think they are and that often the repairs make the situation even worse. Unless you are a racer I believe the best bet is to leave blisters alone. Unfortunately we do not know what caused the flakes on tbosch's hull but I still advocate for a basic solution such as simply painting or fairing and painting.

The other conclusion I reach is that we should be careful how much bottom paint we slather on our boats, especially in fresh water. I use VC17M and am considering skipping painting this year or maybe just doing one foot along the waterline. I had no marine growth last season and the hull is still completely covered with paint. The less we paint the less chance we'll need to strip the bottom.

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John Russell
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Response Posted - 11/24/2008 : 19:25:11

I agree, Randy. I watched as aija was pulled this fall. I ran my hand over a couple of areas on the keel that had no bottom paint and the crud that was accumulated there was no worse than the stuff on the ablative I have. I'm not sure I see the value of all that work, expense and polution in the water I'm in. Since I don't race, I'm not in search of that 0.1 knot. But, since I have most of a quart left from last year, I touch up the bottom again in the spring.

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Steve Milby
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Response Posted - 11/24/2008 : 19:45:45

I stripped my bottom a couple of years ago, and put three coats of top quality ablative antifouling on it to begin with. The first coat was blue, and the other two coats were red. Now I put one coat on each year. The boat is in the water for about 7 months per year, and when it comes out it's clean. At haul out time, I usually see a slight shadow of blue paint, so I know it's not accumulating much paint each year. As long as I still see blue paint, I'll know one coat will be enough. If too much of the bottom shows blue paint, I'll know it needs two coats.

The good paint is more expensive, of course, but, over the long run, it'll save me untold labor.

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Dave Bristle
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Djibouti
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Response Posted - 11/24/2008 : 21:59:23

My approach is the same as Steve's... and I have to suspect that cruising at 20 knots (and occasionally yahooing above 30) wears more than at 5 knots. The way my bottom looks right now, I'll dress up the waterline and touch up a few areas next spring, but I won't add a full coat. A friend sometimes does his waterline touch-up by smearing the existing ablative paint around with lacquer thinner rather than painting--it looks like new without adding a layer.

Edited by - Dave Bristle on 11/24/2008 22:01:48

Voyager
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Response Posted - 11/25/2008 : 21:01:08

This year I've got Passage on the hard in the parking lot of the marina - on asphalt, not gravel so my inclination is to put down the tarp, put on the dust mask and start chipping off the sections that will chip, so that by the end of the season, I hope to be down to the gelcoat.

I'm certain that I'll end up with cliffs and canyons, so that's when I'll get the paint scraper out.

Any advice on staying out of trouble with the yard, with the EPA and with the doctor?

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Dave Bristle
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Djibouti
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Response Posted - 11/25/2008 : 21:48:55

Bruce, my preference is "peel-away" stripper, for the environment, health, and ease of use. However, I've been advised that it's a waste of money to try it when the hull is below 50 degrees (as it can be when the air has warmed to 60), and warmer is better. As you can see, I didn't get around to using it on Passage to remove the cratered hard paint from my DPO. (I added only abblative.)

Edited by - Dave Bristle on 11/25/2008 21:52:37

Steve Milby
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Response Posted - 11/26/2008 : 07:39:25

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Voyager
 This year I've got Passage on the hard in the parking lot of the marina - on asphalt, not gravel so my inclination is to put down the tarp, put on the dust mask and start chipping off the sections that will chip, so that by the end of the season, I hope to be down to the gelcoat.

I'm certain that I'll end up with cliffs and canyons, so that's when I'll get the paint scraper out.

Any advice on staying out of trouble with the yard, with the EPA and with the doctor?
<hr height="1" noshade id="quote"></blockquote id="quote">I've stripped my C25 and C&C35 to the bare glass using chemical strippers, and believe it's by far the easiest way to do it for a DIY'er (bearing in mind that there's no easy way to DIY). (The 35 was so big that I had most of the old paint power-planed off by a pro, so I only had to strip the last layers with chemicals.)

Many marinas won't allow people to work on their boats on premises, but, if they will, they'll undoubtedly require you to lay a tarp under the boat to collect all chips and drips, and, if you use a power sander, you'll have to connect a shop vac to your sander to collect the sanding dust. The marina will probably have a specific container where you should dispose of any dust, chips and toxic debris. You'll need to wear a respirator (not just a paper dust mask), and, if you use chemical strippers that can drip on you, you need to protect your skin so it doesn't get on you. (It gives chemical burns.) The marina probably has a hand-out sheet that lists all their requirements. You'll undoubtedly be working on your knees a lot, so knee pads will help.

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