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Old 06-11-2018, 05:50   #1
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Should I keep sanding?

It's a 1985 Catalina 27 hull. I will dig up and fill the blisters. My question is "should I keep sanding the large paint flaked sections?"
Thanks
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Old 06-11-2018, 06:33   #2
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Should I keep sanding?

Get a long handled carbide scraper and go at it with that. Big chunks of paint will probably pop right off. Your shoulders will hate you but it will likely be faster.

Often with paint build up like you have attacking it with an orbital and 40 grit does little more than burnish the paint, depending on what it is. If the scraper route does not work then a grinder polisher with an 8” soft pad and 36 grit adhesive disks works far better than an orbital although you need to develop some touch with it to not burn divots and get a fair surface.

And yes if it were me I’d take it all off. Looks like you have some suspect previous repairs under the layers of paint and those will come back to haunt you later if you don’t take everything down so you can see what’s what.
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Old 06-11-2018, 06:37   #3
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Re: Should I keep sanding?

This is a sign that the bond between the paint and the hull is failing in those areas. If you don't sand more, you will typically find that some other sections fail after repainting.

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Old 06-11-2018, 06:44   #4
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Re: Should I keep sanding?

That is a lot of paint build up, I would forgo the sander in favor of a grinder and a paint/rust stripping wheel, just be careful not to dig into the hull as they will chew fiberglass/grp and be fairly happy to do so. Alternately a soda blast or similar probably wouldn't be a bad idea either. Just my 2¢
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Old 06-11-2018, 07:06   #5
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Re: Should I keep sanding?

Quote:
Originally Posted by ferrailleur View Post
It's a 1985 Catalina 27 hull. I will dig up and fill the blisters. My question is "should I keep sanding the large paint flaked sections?"
Thanks
The last two times I did mine I took it down to a totally smooth surface.

This time it looks like I'll just have to rough up the surface a bit and then apply the bottom paint

This is four years since I last painted the bottom. Two of the pictures are how it looked when I launched it in 2015

And two pictures that show a bit of the upper bottom that was sanded smooth. I was just starting on the topside hull which had to be sanded down all the way to the original 1974 beige gelcoat
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Old 06-11-2018, 07:21   #6
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Re: Should I keep sanding?

In that second picture of yours, you can see where someone painted over a flaked out section. That is how my boat looked. It was not possible to just sand it back lightly to get to "good paint" because there wasn't any, and the new paint won't bond to that. It's a helluva job to sand it all off, but you'll also want a clean surface to put an epoxy layer down after the blister repair and get the whole bottom fixed for good. Sail Life on YouTube did an amazing job documenting this work but he tends toward uber-perfection.
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Old 06-11-2018, 07:59   #7
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Re: Should I keep sanding?

Art this point yes I would remove all that. Use a big sturdy scraper if possible. You can pay a worker to help and save your back, still will be a ton less than blasting $ etc. Also you'll likely need to rent a big grinder like 8" with a 40 grit disc. But it's easy to damage with that if you aren't skilled at it.
I wonder if this is a better job for a bunch of paint remover first?
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Old 06-11-2018, 08:01   #8
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Re: Should I keep sanding?

Quote:
Originally Posted by ferrailleur View Post
It's a 1985 Catalina 27 hull. I will dig up and fill the blisters. My question is "should I keep sanding the large paint flaked sections?"
Thanks
It's either time or money. If you plan on keeping the boat and have the financial means, I second the recommendation to get it soda blasted/barrier coated. We didn't have any blisters, but our bottom was similar to what's shown in your pictures. I tried working on a large area each off seasons but could never get it right. You will likely be repeating your current process each year if you don't bring everything down to the gelcoat all at once. And doing that manually will take an appreciable amount of time/effort. Check around your area, but we paid ~$50/foot for soda blasting, 2 barrier coats and 2 coats of paint (Sea Hawk products). Those are metro Boston #'s, so shouldn't be too different where you are. Bottom looks like new and maintenance is just touch up's, leaving one less thing to have to deal with each off season.
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Old 06-11-2018, 08:34   #9
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Re: Should I keep sanding?

I just did mine, similar but not as bad as yours and my barrier coat was in great shape with no blisters paint falling off by the handfuls. I brought down to just above the barrier trying not to sand into/thru it then put down primacon as the base layers of paint had a really good bond then painted. I used a (two as one died half way through) belt sanders to get the bulk of it down, then orbital with 40 to finish it up before primer. Yard asked me when I sprayed and were suprised when I said I rolled it.
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Old 06-11-2018, 09:45   #10
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Re: Should I keep sanding?

I would recommend blasting it with water and glass frit to take it right back to where all the damage is visible. cover and dry it out, Then do all the glass repairs. Epoxy resin is pollution on a polyester resin built hull. Save you money and spare yourself future aggravation...use The same material that the hull is made from for all repairs and finishing. BTW there are some materials that Epoxy will NOT stick too.
It is not the go-too miracle cure for all ills.
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Old 06-11-2018, 10:13   #11
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Re: Should I keep sanding?

Another great benefit to having a yard crew do the job is the supply & use of drop tarps; cleaning up the mess after all the blasting/sanding is done; not forgetting the disposal of contaminants; . . . Yup, if you can afford it, get 'er done after all, ask any Sunday afternoon dock walker & they'll tell you, "anyone who owns one of them yachts must be rolling in money" . . . it's true! I just heard it said the other day while sitting quietly in the cockpit sipping on a drink. Oh, how little they know.
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Old 06-11-2018, 10:21   #12
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Re: Should I keep sanding?

I took 30 years of hard bottom paint off my boat. As others have said try using a scraper to get the flakey stuff off. In addition to a orbital sander hooked up to a shop vac, I used a drywall sanding screen. Worked pretty good. But my boat was in my driveway not a boatyard.
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Old 06-11-2018, 10:21   #13
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Re: Should I keep sanding?

You can easily do the job yourself if the boatyard you are using isn't too expensive.

Down here during the months of November - February, the yard storage fee is the same as the slip fee at my old marina so I spread the work out over 4 months

Sometimes I'll even sand for just 2-3 hours on weekend days. I'm over 60 btw.

I totally sanded down the entire bottom sometimes all the way to fiberglass then sanded the topside hulls totally free of paint down to the old gelcoat. Then the bottom got a coat of Micron CSC. Some parts got a second coat as I bought a gallon and one extra quart of that bottom paint

I used a 6" orbital Sander with 40 -80 grit disks. Cleanup was the easy part. Just roll up your tarp and empty it into the nearest trash barrel after each days work. Then it's beer time and boatyard watching
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Old 06-11-2018, 10:37   #14
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Re: Should I keep sanding?

I think it's always tempting to believe that old paint film has some value, residing as it does underneath a layer of new antifouling paint. That's incorrect; it's basically a negative in all respects.
  • It makes your boat heavier.
  • It absorbs some of the new paint and makes it less accessible to the water, and therefore ineffective.
  • It alters the shape of your bottom, which slows your boat down.

My strong recommendation is to take the boat down to the gelcoat using one of the previous suggestions. Ideally, whatever you'd use would have an efficient dust collector system (like the models with a large vacuum attached) so that you're not spewing old paint residue in the yard. It's worth it to take time to make sure the boat is fair before you coat it with new paint.

Cheers,

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Old 06-11-2018, 11:15   #15
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Re: Should I keep sanding?

yes, remove all of the paint.
I can see some small blisters still hiding under the old paint.
It's worth getting a quote on soda blasting, you may decide the price is reasonable. I did.
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