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Hull Sanding for barrier coat

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pegasus
1st Mate

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USA
65 Posts

Initially Posted - 06/26/2007 : 10:19:34

Hi Folks:

I'm sanding-down some osmotic blisters and noticed that I may have as many as four coats of something on my hull. The outer coat is a blue ablative anti-fouling finish. Under that appears to be a white semi-rough textured epoxy undercoat, Under that is the, I assume, original dark blue paint applied by catalina at the factory with the fiberglas core under that. It looks like a P.O. may have filled some blisters with auto body filler (Bondo), and it looks like Catalina faired the hull with some sort of filler where the keel attaches to the bottom of the boat.

My questions are:

Is it correct to assume that the boat, a 1986 TR/FK,had a dark blue finish applied over the fiberglass hull, and then someone applied a thick finish of some sort over that?

I know I have to sand-off the anti-fouling paint, but does/should everthing else need to come off? I know these coats add weight...

What's the best/easiest way to sand/remove all this from the hull?

Who's free to stop-by and help me sand? (kidding, of course)

Thanks for your thoughts and views

Edited by - on

DaveC25
Navigator

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USA
152 Posts

Response Posted - 06/26/2007 : 13:59:04

When I did my bottom, I ended up having to scrape the old stuff off with a scraper because it was very thick. When I finally got through it all, the bottom of the hull was white like the sides, except, of course, the boot stripe.. At that point I could see the blisters well because the gelcoat had a small crack or two wherever there was a blister. I then had to take a dremel tool and open the blisters, dig out the rotten glass, and then fill it with a marine grade filler (it was a bluish-green color, from Interlux).

After that I sanded the hull with 80 grit on a sander, washed it, and then applied the barrier coat. I actually think I need to do another coat or two.

I hope this helps a little. As far as it being blue, I don't know about your hull. Mine was white. But you should not see the fiberglass matt, otherwise you went through your gelcoat.

As far as sanding, I will have to pass. Besides, it will make you appreciate your boat more by having to work so hard..... and cringe more when you run aground. :)

-DaveC25

Edited by - DaveC25 on 06/26/2007 14:01:18

pegasus
1st Mate

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USA
65 Posts

Response Posted - 06/26/2007 : 14:22:35

Thanks, Dave - I was wondering if I need to sand all the way down to the fiberglas, or just scuff the surface where the bond to the hull is good. Also, what type of sander did you use? Any recommendations on how to make the job as quick and easy as possible? I have a grinder with a sanding pad, but it's a bit aggressive, otherwise I have a 1/4 sheet palm sander that's kinda of slow going.

Edited by - on

stampeder
Master Marine Consultant

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1608 Posts

Response Posted - 06/26/2007 : 14:41:24

I did a major bottom job one year ago: I used a $40 random orbit sander to go through 20 years of PO bottom jobs. Topmost layer of paint was ablative, other layers were hard paint. I started using a 60 grit, then moved up to 220 grit as I got closer to the gel coat.
You want to remove paint, but not the gel coat. That said, I did remove a very small amount of gel coat, leaving a very smooth nice looking bottom on my 1981 SR/SK. I had a few very small blisters and bubbles in the gel coat that came off easily. I fixed a few scratches and gouges with White Marine-Tex.
My random orbit sander has hook and loop fastener (velcro). I went this way because you will have to remove and replace sand paper frequently - about every 15 minutes, to do an exacting job of removing paint.
I then applied barrier coat/primer, then two coats of hard paint.
One year and three launchings later, my boat's bottom looks great.

Edited by - on

DaveC25
Navigator

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USA
152 Posts

Response Posted - 06/26/2007 : 16:03:20

I used the same kind of sander as Stampeder. It took a long time. I did scrape alot of it off, however I would not recommend this too much because I did gouge the gelcoat in a couple of places. I filled them and barrier coat it, so hopefully it'll be okay. It seems okay, anyways. :)

Edited by - on

pegasus
1st Mate

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USA
65 Posts

Response Posted - 06/28/2007 : 10:36:16

Thanks guys - it's a job I'm not really looking forward to, but one that needs to be done. I was hoping someone would have a tip like 'just smear on a quart of Zippy Strip Wax, and watch the old layers slough-off.' Guess I need to just suck-it-up and start sanding. On the bight side, my kids gave me an iPod for Father's day - I guess i could download some CD's on it and make the sanding time go-by quicker...

Edited by - on

John Russell
Master Marine Consultant

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USA
3444 Posts

Response Posted - 06/28/2007 : 10:40:29

Didn't I see something a while back regarding some kind of stripper? It seems to me it was Randy (Nauti Duck)??????

Edited by - on

Steve Milby
Past Commodore

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USA
5902 Posts

Response Posted - 06/28/2007 : 15:53:31

If there are presently only about 4 coats of some kind(s) of paint on the boat, that's actually much fewer than most of us have on our boats. I just completed a down-to-the-fiberglass bottom job and barrier coat, and have already applied five barrier coats and 2 coats of antifouling. You should only remove what needs to be removed.

First, examine the existing bottom paint. If it's fairly smooth (i.e., not peeling), just give it a light sanding and paint over it with any compatible bottom paint. If it's peeling slightly, I'd do the same, except I'd sand a little more wherever it's peeling the most. If it's peeling badly, then you should remove just the anti-fouling. I would avoid removing anything the factory applied. When you're talking about sanding material off the bottom of your boat, it's a lot like getting a haircut. If you take off too much, you can't put it back on.

If you're repairing a few minor blisters, I'd suggest you cover them with a little barrier coat of some kind. You can use 3-4 coats of the Interlux 2000 system, or you can use 3-4 coats of coal tar epoxy (VC Tar). Sand them lightly, to feather them smoothly into the rest of the surface.

Edited by - on

Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 06/28/2007 : 17:38:20

You might want to use the Search function to find several related threads--search for "stripper" in the text in the General Forum. I assume you're aware that bottom paint dust is toxic--in the lungs, eyes, and on the skin.

PS: Why are you doing this at the end of June? Put a coat of anything on, splash her, go sailing, and deal with this in "prep season".

Edited by - Dave Bristle on 06/28/2007 17:41:42

stampeder
Master Marine Consultant

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1608 Posts

Response Posted - 06/29/2007 : 15:19:31

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">PS: Why are you doing this at the end of June? Put a coat of anything on, splash her, go sailing, and deal with this in "prep season". <hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">

Sage advice. Go sailing. Everything has a season.

I'd go sailing right now, except that we're experiencing a thunder and lightning storm.

Edited by - on

Dustysailz
1st Mate

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USA
85 Posts

Response Posted - 07/01/2007 : 10:30:06

My bottom was just finished in early June. Ode To Joy is an '84 std rig with fin keel. Being that she is older I wanted to see the bottom and address any issues that needed to be. Well, I got my wish. She was soda blasted and there were blisters/imperfections. My first step was to sand the bottom with a random orbital sander then dremel each blister/imperfection and sand again. Then I cleaned the bottom with acetone and filled each hole with West system, after which she was sanded again and wiped again with acetone. Then I applied the Interlux barrier coat kit (which is two parts). I was then advised to put on one coat of hard paint between that and the bottom paint. I used an Interlux hard paint ( a quart put one coat on the bottom with a roller). Having just done all this work I now wanted a good paint and bought Micron Extra at the marine store where I now shop for $189 with a $20.00 rebate coupon. I used it all and managed to put two coats on saving a little for the bottom of the fin. All told she has 2-3 coats of barrier paint, one coat of hard paint and 2 coats of ablative paint all applied with a 3/8 nap foam roller. She has now been in the water 3-4 weeks and as of yesterday the bilge remains bone dry. I'm sorry that you're now faced with doing the bottom, but as you have started it may be best to do it right the first time so that you need not do it again. Goodluck and good sailing.

Edited by - on

pegasus
1st Mate

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USA
65 Posts

Response Posted - 07/06/2007 : 18:04:43

As to why I'm doing this now...June/July on Lake Murray, SC is the season of hot temps, light winds, too many jet skis and speed boats. The rest of the year is cool temps, few other boats on the lake and good sailing winds. If I'm gonna sit out a few months, now's the time to do it!

Edited by - on

Champipple
Master Marine Consultant

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USA
6855 Posts

Response Posted - 07/06/2007 : 20:51:39

I didn't read all the posts above but you don't have 4 coats of anything going on.

Blue outer is bottom paint
White coat is either A - the gel coat or B - the barrier coat
The blue crap under that is the foam/gel coat filler layer between the white gell coat and the fiberglass or wood (depending on area)

You don't want to go below the white coat unless there is a blister.

Edited by - on

pegasus
1st Mate

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USA
65 Posts

Response Posted - 07/09/2007 : 13:34:55

I believe a previous owner had blisters in the gelcoat then repaired them by filling them with (something like) auto body filler. He sanded it smooth and then covered it with something like an underwater epoxy finish - because it's gray, hard and thick. Over that is the ablative blue antifouling paint. No, I don't want to sand any more than I have too, but I want to remove anything that's apt to blister or peel in the future.

Edited by - on

stampeder
Master Marine Consultant

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1608 Posts

Response Posted - 07/09/2007 : 23:39:38

Not autobody filler.
Use Marine-Tex.

Edited by - on

pegasus
1st Mate

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USA
65 Posts

Response Posted - 07/10/2007 : 07:51:24

Yeah, I know...I'm leaning towards a West System repair. Auto body filler absorbs water, so I can't imagine why anyone would use it. Unless they wanted to get the job done quickly and cheaply, then sell the boat to an unsuspecting chump, like me!

Edited by - on

Frank Hopper
Past Commodore

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Pitcairn Island
6776 Posts

Response Posted - 07/10/2007 : 11:55:15

Bondo actually does have a marine grade filler which is pretty good stuff, and blue. It has lots of long fibers in it instead of just filler or micro balloons. I faired some of the cast iron swing keel with it.

Edited by - on

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