Association Forum - Bottom Paint Prep Procedures

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Catalina 25 Specific Forum

Bottom Paint Prep Procedures

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Thee and Me
Deckhand

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18 Posts

Initially Posted - 07/06/2009 : 19:33:16

I am in the process of preparing the hull of a '79 C25 Std. SK (Thee and Me) for a summer/autumn in the salt water. She will be moored on a buoy near our home north of Seattle. I am a rookie to painting fiberglass/gelcoat surfaces. I am requesting input from the C25 Forum on the prep of the hull and swing keel for the barrier coat.

Based on a close visual inspection before the start of the prep work, there appeared to be several layers of bottom paint. There were also many areas where the top layers of paint appeared to have flaked off. These areas looked like they were spot painted, in some cases just painted over with a new bottom coat, but no real attempt to feather the edges of the flaked spots were observed.

The exposed areas of the swing keel were completely painted, but I did notice some rust spots penetrating the bottom paint. The aft part of the keel trunk also appeared to be painted, but the forward part (that I could see) of the trunk appeared to be gelcoat (!?)

To the best of my knowledge, this boat has not spent any extended period of time in salt water (perhaps 3 months continuously at most). I did inspect for evidence of blisters and found none.

I performed an initial stripping run using one of the more "environmentally friendly" brands (i.e., no methylene chloride). The stripper appeared to do an adequate job (left it on for about 12 hours max.) with no apparent damage to the gelcoat. My nephew did the majority of the work scraping the hull. For some reason he used a cabinet type scraper (i.e., single edge razor blade), in lieu of a hook scraper.

Anyway, I now have at least two different layers of paint exposed on the bottom of the hull, including some bare gelcoat. The keel surface that is accessible appears to have at least two layers of paint on it (e.g., a Rustoleum and/or a red based bottom paint, along with what I understand was the original blue bottom paint.) The surface of the keel appeared to be a bit rough. I'm not sure if this is due to some previous electrolysis action (there did not appear top have been any zincs installed on the keel).

My plan is to apply a barrier coat to both the keel and the bottom of the hull, along with at least two coats of ablative copolymer bottom paint to all exposed surfaces below the water line.

I want to make sure that the barrier coat properly adheres to the hull and keel surfaces. That being said, is it prudent to:

(1) sand (feather) the existing surface(s) as smooth as possible before the barrier coat, or (2) perform another stripping run and try to get down to at least the gelcoat and original bottom paint before sanding and applying the barrier coat?

Also,

(3) With regard to the keel, I'm, recalling that I read somewhere I should fill the marks in the keel with a "chemically compatible" substance and fair before applying the barrier coat. What is the recommended procedure here?

I'm already late in getting her in the water this year, but I want to do the best job possible before I put her in the salt water of the bay. My previous experience with painting other surfaces tells me I should try and get as much paint off as practical/possible before prep sanding and application of the barrier/primer coat.

FYI, I'm installing the three major retrofit kits for the swing keel assembly in conjunction with the work on the bottom.

All input would be appreciated. As a new C25 owner, this forum has been invaluable. I'm also planning on joining the Association. Thanks in advance for your help in this!

Edited by - on

Steve Milby
Past Commodore

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USA
5908 Posts

Response Posted - 07/07/2009 : 11:29:54

I stripped both my Catalina 25 and my current boat, a C&C35, to the gelcoat, barrier coated them and finished them with antifouling. If the bottom doesn't have a terrible accumulation of paint, you can get away with a light sanding and fresh coat of antifouling, but it sounds like your boat is due for the full treatment. It'll be a lot of unpleasant work, but, by comparison with the way it is now, the boat will sail like a dream when it's done. I used chemical stripper especially designed for fiberglass. You should remove all the old paint before barrier coating. Your boat might not need to be barrier coated, but when I stripped mine, I also barrier coated it for long term durability (and then sold it shortly after doing all the work. (So much for long term planning!)

My C25 keel was a cast iron fin keel boat. The iron keel is a crude casting, and will have depressions that will need to be filled with a filler of some kind. I used an Interlux product for underwater surfaces, because it was easy to apply and sand and long lasting. (I forget the name offhand, but there are a number of good products available.) I'm sorry I can't take more time, but am in the middle of a repair job on my boat. Others will join in.