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sand blasting bottom

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Larry
1st Mate

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USA
37 Posts

Initially Posted - 04/12/2006 : 16:05:51

I just got off the phone with the sand blasting guy who I may have do my bottom. He says that he ordinarily just blasts the loose stuff of the cast iron keels, to bring it down to bare metal is much more expensive. Should I pay the extra money? I have a 1984 swing keel. I don't plan on racing. I am a little short of money right now. What do you guys suggest?
Thanks for any help.

Larry
"Kate Caroline" 1985
Great South Bay, Long Island, NY

Edited by - on

Steve Milby
Past Commodore

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USA
5902 Posts

Response Posted - 04/12/2006 : 18:40:20

I wouldn't let anyone with a sand blaster get anywhere near my boat or keel. Sandblasting does significant damage. There's no really easy way to strip the paint off your bottom and keel, but the best way is to use paint stripper that is specifically designed for stripping paint off of fiberglass. You can get it at automotive paint stores where professional car painters get their supplies. You usually can't get it at ordinary neighborhood auto parts stores. It costs about $20 a gallon, and will take several gallons. You start brushing it on, and keep brushing another coat on over the previous coat, and don't let it get dry. Keep doing it until the paint gets soft and can be scraped off fairly easily. If it's really hard to scrape, you haven't softened it up enough yet. Wear rubber gloves with long sleeves, because the stuff burns if it gets on your skin.

Edited by - on

Leon Sisson
Master Marine Consultant

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USA
1893 Posts

Response Posted - 04/12/2006 : 18:47:57

<blockquote id="quote">quote:<hr height="1" noshade id="quote">...ordinarily just blasts the loose stuff of the cast iron keels, to bring it down to bare metal is much more expensive. Should I pay the extra money?<hr height="1" noshade id="quote"></blockquote id="quote">That depends on what your longer term plans are for the keel, and how much you're looking forward to doing this all over again in the near future. In my humble but experienced opinion, if you're not prepared to do it right the first time, you're probably better off saving up your sandblasting funds for another time.

And by "do it right" I mean sandblasting to clean, solid, 'white' cast iron -- with no darker spots of iron oxide remaining -- then within hours etching with hydrochloric acid to get at the microscopic oxide pits the sandblaster missed, followed immediately with a coating of Ospho (or other rust locking treatment). Then encapsulation with several coats of epoxy resin, and optionally fairing and fiberglass encapsulation to protect from future abrasions (including bottom paint sanding). I've done this on two boats, so I can assure you it's a lot of work, and the results are pretty much permanent. That is, subsequent maintenance is limited to patching up the spot which always runs aground first. (And a bronze 'shoe' there cuts way down on that damage.)

If you're not into "doing it right" this time around, I'd suggest knocking off what rust you can with a chipping hammer and the coarsest wire brush you can get your hands on. (I'd use a monster cup brush on a powerful, two-handed, variable speed, 7" sander/grinder/polisher.) Then applying a couple coats of Ospho, or similar rust locker, followed by whatever bottom paint you've decided on.

One big disadvantage of this quick and dirty method is when you later decide to do it right, all that toxic bottom paint has to be removed from the moonscape-like rust pits before you can even begin the more thorough method, above.

-- Leon Sisson {he's just a fountain of encouragement!

}

Edited by - on

djn
Master Marine Consultant

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USA
1561 Posts

Response Posted - 04/12/2006 : 18:52:39

Hi Larry, I have been going back and forth about what I should do with my boat bottom. I looked at a boat today that was striped using Captain Johns striper......WOW talk about taking it down to the original gelcoat without any damage...at all. I am very impressed. I will use it next week. His email is http://www.captainjohnsboatbrite.com/

WM is now selling it.

Edited by - on

Champipple
Master Marine Consultant

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USA
6855 Posts

Response Posted - 04/13/2006 : 06:41:03

See if the guy does any soda ash blasting or crushed walnut (might be some other nut) shell blasting. It is much more boat friendly. If you have the right guy doing sandblasting with a lot of experience doing boats, it will be okay, but one second of not paying attention and your gel coat is toast

Edited by - on

djn
Master Marine Consultant

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USA
1561 Posts

Response Posted - 04/13/2006 : 06:53:07

The guy at my marina, puts sand in his water sprayer and it seems to work well, but he wanted 1K to do my little c25.

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Steve Milby
Past Commodore

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USA
5902 Posts

Response Posted - 04/13/2006 : 10:17:34

Catalina cast iron keels were generally pretty crude castings, and Catalina used fairing compound to fill all the depressions and smooth them out. Then they coated them with coal tar epoxy to seal the iron. If you removed all that epoxy and fairing material down to bare iron, you had to re-seal the bare iron with something to prevent it from oxidizing, then fair the keel again, then paint it. I'm sure that's ultimately the best way to do it, but, as Leon said, it's also an ungodly amount of work. If you plan to keep the boat for many years and "amortize" your hard work, then it's probably well worth it, but, if you might sell this boat and move up to a different one in a few years, it might not be.

If you strip all the old paint off the keel so that all that's left is the fairing material, coal tar epoxy and bare iron, and clean the bare iron with a wire brush in a drill, and then re-seal it with coal tar epoxy, replace any loose fairing material and paint it, that will give a good, reasonably long lasting result for most purposes. It might need occasional repairs, but that's the trade-off you make.

I do think every boat with a cast iron keel should have a sacrificial zinc or magnesium attached, depending on whether it's in salt or fresh water, because it'll prevent any reaction that might cause damage to the fairing compound.

Personally I don't like walnut shells or soda, but many knowledgeable sailors do, so I think that's a matter of preference. But sand is much too aggressive. Blasters like sand because it's cheap and fast. You might never realize it has damaged your boat before you sell it.

Edited by - on

Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 04/13/2006 : 12:02:27

Around here, soda blasting is about twice the cost of sand, and both require extensive "tenting" to seal every last particle in. I've heard horror stories about sand blasting--I think "Val on the hard dagnabit" has one...

Whichever way you take the paint and scales off, I'll suggest using something like Rustoleum Rust Reformer on any bare iron and remaining surface rust--it goes on like milk, dries clear, and turns the metal or rust into a hard, black surface ready for paint. A zinc annode (replaced annually) is a good idea and will reduce (not eliminate) corrosion to the keel, cable, and possibly even the winch, but there's a lot of iron in that keel--it isn't going away any time soon!

Edited by - Dave Bristle on 04/13/2006 12:03:34

Frank Hopper
Past Commodore

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Pitcairn Island
6776 Posts

Response Posted - 04/13/2006 : 12:30:54

This was years worth of ablative soda blasted off, it did not make much of a mess on the ground; we don't want anything growing there anyway. I think people make way too much of all of this. Remember when the teachers used to pass a bowl of mercury around the classroom? We are still around; and I want my cyclomates back... damn it.

Edited by - on

Frank Hopper
Past Commodore

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Pitcairn Island
6776 Posts

Response Posted - 04/13/2006 : 12:41:23

This is ridiculous: its VC 17 for heaven's sake!

This is how you do VC 17

Edited by - Frank Hopper on 04/13/2006 12:45:37

Champipple
Master Marine Consultant

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USA
6855 Posts

Response Posted - 04/13/2006 : 18:34:31

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Dave Bristle
 Around here, soda blasting is about twice the cost of sand, and both require extensive "tenting" to seal every last particle in. I've heard horror stories about sand blasting--I think "Val on the hard dagnabit" has one...

Whichever way you take the paint and scales off, I'll suggest using something like Rustoleum Rust Reformer on any bare iron and remaining surface rust--it goes on like milk, dries clear, and turns the metal or rust into a hard, black surface ready for paint. A zinc annode (replaced annually) is a good idea and will reduce (not eliminate) corrosion to the keel, cable, and possibly even the winch, but there's a lot of iron in that keel--it isn't going away any time soon!
<hr height="1" noshade id="quote"></blockquote id="quote">

I was under the impression that soda blasting was an extrememly clean process

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Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 04/13/2006 : 21:06:02

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Duane Wolff
 I was under the impression that soda blasting was an extrememly clean process
<hr height="1" noshade id="quote"></blockquote id="quote">
Clean only if the operator contains and then picks up everything. The baking soda will dissolve and wash away, while the sand remains sand and puts silica dust, a mild polutant, into the air. Either way, the toxic paint chips and dust are not so mild. The main advantage of soda is reduced damage to the gelcoat. (I don't know how it could take off the mess on my hull without also damaging the gelcoat, but so I'm told...)

Edited by - on

tinob
Master Marine Consultant

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USA
1883 Posts

Response Posted - 04/14/2006 : 11:08:36

When they sand blasted my boat the tent that they enclosed the boat in was also a vacuume chamber. Nothing ended up on the ground. And it cost $ 350 if I remember corectly.

There wasn't a problem with gelcoat, just left a nicely textured surface for paint to adhere to.

Dave mentioned a problem that I had had with sandblasting. The problem was that in cleaning the bottom it exposed a gazillion small(pea sized) blisters. It took half of the season to Dremmel them open and dry. And then epoxy them and fair them and sand them smooth. After which the botom was barrier coated and given its first coats of ablative paints.

GO ABLATIVE

Val on the hard DAGNABIT # 3936 Patchogue, N.Y.

Edited by - on

OJ
Master Marine Consultant

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USA
4382 Posts

Response Posted - 04/14/2006 : 17:18:26

I have a friend who restores building exteriors and one of the processes he uses is soda blasting. He explained that the baking soda has a very sharp edge making it a very effective abrasive - but as soon as it hits a hard surface it turns to dust.

Also, FWIW, I've had very good success applying vc17 with an airless sprayer.

Edited by - OJ on 04/14/2006 17:20:35

ajski1000
1st Mate

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USA
52 Posts

Response Posted - 04/14/2006 : 21:46:21

Hi all,

I purchased my 85 last year with significant rust on the keel. The rest of the hull was flawless. After talking to many ppl on what the best course of action was with the keel. Everyone told me that it had to be blasted and brought to bare metal.
Ive always been pretty handy and being a college kid I went at it on my own.

My solution took no more then two days, and no more then 4-5 hours work. I had a 7" professional buffer then use on cars and I retrofited it with some very low grit paper made for the cast. It was like 15 bucks at home depot for the sheets i needed.
Took me a few hours to get all the crap off and brough it right to bare metal, once bare cleaned off with solvant and then applied my first coat of epoxy. Came back the second day and re-applied.
Once finished i lightly sanded to get out imperfections and then applied bottom paint.

Looks great, was in the salt water all season, when she came out it was still flawless.

Just my two cents

If i can help anyone with this dont hesitate to ask. :D

Edited by - on

Larry
1st Mate

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USA
37 Posts

Response Posted - 04/15/2006 : 06:37:43

Thanks all for your input. I called the sand blaster and cancelled. With regard to the keel, I'm afraid that what I would like to do and what I have the time to do may be at odds. I am considering getting as much rust off as possible and using that rust reformer and a zinc. Maybe next year I'll have more time/money to do it right. Cheers.

Edited by - on

thaind
Navigator

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Canada
145 Posts

Response Posted - 04/17/2006 : 06:23:45

I had to do some repair to the keel/hull joint on my 78FK. I used a combination of sandblasting and grinding. The keels are extremely rough castings so getting down to bare metal results in only a clean surface, and I used the fibrated Bondo that is reccomended by the company for underwater boat use to fair the joint. It has survived the first season completely intact, and has been an effective cheap solution.

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