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 Powder Blasting and Barrier Coat		  New Topic  Topic Locked
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bigelowp
Master Marine Consultant

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USA
1736 Posts
Initially Posted - 01/21/2011 :  15:47:35  Show Profile
As I look at all the fresh powder (snow) that has fallen up here in New England I am thinking about one of those boat projects that is inching it’s way up my “to do” list: powder blasting the hull, applying a barrier coat, and repainting. I kinda get the process on the fiberglass hull, but when I get to the iron fin keel, what would I be “priming” with? Is the standard practice to use barrier coat on all or prime the metal first and then apply barrier coating – or just prime and not apply a barrier coating? Based on age and sailing that I do I had not planned on fairing the keel. Would anyone with the iron fin keel who has been down this road before be willing to enlighten me . . . ?
Peter Bigelow
C-25 TR/FK #2092 Limerick
Rowayton, Ct
Port Captain: Rowayton/Norwalk/Darien CT
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tbosch
Navigator

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163 Posts
Response Posted - 01/22/2011 :  07:58:30  Show Profile
I took on this project and can provide some insight. The key will be removing any loose fairing material that is on the keel. You don't have to remove it all but if you are going to go through the effort and expense of barrier coating and bottom paint then you want to make sure that anything you are painting over is solid.

I chipped away areas covering the keel that were obviously loose or cracked. Then I used an angle grinder to further work away surrounding fairing material to make sure I was getting into well adhered material. I then used the angle grinder with a wire brush attachment to "brighten" the cast iron. When you seal the metal you don't want any rust or oxidation on it. I brushed clear epoxy over the bare metal and, while it was still wet, used a wire brush to scrub the epoxy into the metal. This starts to make the epoxy dark but that is ok. You want to make sure that the epoxy is fully in contact with the metal. While the epoxy is still tacky you can add additional coats of clear epoxy. I did 3 for good measure and with the 2nd and 3rd coats I covered the entire keel. I re-faired my keel so the 2nd and 3rd coats covered that work, too.

If you aren't going to fair the keel then when the epoxy has fully cured, wash it well and scuff it up with sandpaper and you are ready for the barrier coat.

I posted a few pictures recently in this thread when a question came up about a "catalina smile":
http://catalina-capri-25s.org/forum/topic.asp?TOPIC_ID=20954& whichpage=2
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islander
Master Marine Consultant

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USA
3992 Posts
Response Posted - 01/22/2011 :  15:23:46  Show Profile
<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">while it was still wet, used a wire brush to scrub the epoxy into the metal. This starts to make the epoxy dark but that is ok. You want to make sure that the epoxy is fully in contact with the metal. <hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">
Todd is right on here.
Sail Mag. Don Casey quote..
The best long term solution is to clean the metal bright, Then immediately coat it with epoxy, Wire brushing the metal through the wet epoxy. This removes the flash rust and creates the best bond between the metal and epoxy. This initial coat should be followed by several additional coats of epoxy. As long as the epoxy is around 20 mils thick and remains intact, the coated keel should not rust.
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bigelowp
Master Marine Consultant

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USA
1736 Posts
Response Posted - 01/24/2011 :  15:34:27  Show Profile
Ah ha -- so remove the epoxy then barrier coat. My "south side of the moon" is looking better all the time! Clearly, the metal prep is crucial.
Edited by - bigelowp on 01/24/2011 15:34:59
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BernieM
1st Mate

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29 Posts
Response Posted - 02/09/2011 :  09:48:10  Show Profile
This is very good info; I'm planning on getting rid of rust blisters on my keel this spring. Would a couple coats of VC tar over top of the brushed-in epoxy work as a good barrier coat before I reapply VC 17, or do I need some other sort of paint to go on first?
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Notice: The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.