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harbin2 01-25-2009 03:23 PM

Bottom Paint Questions
Im about 45% done removing the bottom paint off my new (used) 1981 Islander 30. I read a lot about it before I started but Im stilling learning.

Under the bottom paint is a 5 coat West System barrier coat. About 20% of the paint was easy to remove with a scraper almost flaked off due to poor adhesion. Another 30% was removed with a scraper with a lot of work. The rest is coming off with a random orbital sander using 80 grit paper. Im about 20% done with that its brutal. When Im done sanding, I plan to apply two additional barrier coats.

I have several questions:
1. Do I need to remove ALL paint? There are some depressions or pits (small veins and depressions) that are holding a small amount of paint. Removing that paint will mean removing 1, 2, or 3 layers of barrier coat. Could/should I use chemical to remove the paint from some of these pits?

2. How to deal with thru hulls and screens.

3. There are several areas (bow and rudder) that have some previous repair filler. From the way it sands, it appears to be a fairly soft filler material. Should I glass over this before applying my new barrier coat?

4. What is the best way to sand the bottom of the keel? The 6 radius between the keel and the bottom?

5. What is the best way to sand but not too aggressively, the leading and trailing edges of the keel, rudder, and hull?

6. How to deal with the boot stripe. The barrier coat meets the boot stripe. The bottom paint overlaps the gel coat. Im sanding the bottom paint off the both and trying hard not to damage the gel coat.

7. What causes bottom paint to flake off? I have looked at numerous boats in the marina. Most have cracks in the paint where the initial, of several layers, of paint have not adhered to the underlying surface. I had a lot of this probably because the boat had been out of the water for 3 consecutive seasons. When I apply my first coat of bottom paint, I want to ENSURE it is going to have 100% adhesion over the entire bottom and that it will last. How can I best assure this happens?

I know this is a lot. Answers to any one or two items would be appreciated.

sailingdog 01-27-2009 09:46 AM

If you're going to be re-barrier coating the boat, you really should remove all the paint IMHO.

The through-hulls should only be painted if they're Marelon. If they're bronze, leave them unpainted.

Replace the soft filler material with either glass or thickened epoxy.

Foam-rubber sanding blocks are good for the leading/trailing edges of the keel, rudder and hull.

Bad prep is usually the reason for paint flaking. Either the surface wasn't cleaned properly or the paint that was on it was incompatible with the new paint and should have been removed.

sailingfool 01-27-2009 10:16 AM

Paint Thickness
54 Attachment(s)
While poor prep will lead to poor adheasion, I think the most common reason for paint flaking is the paint has become too thick. You get 6-8 layers of paint, any paint, and it is likely to start flaking. The magic of an ablative paint is if properly used it will not produce a buildup resulting in paint flaking. The trick with ablative paint is to not put any on unless it is needed - i.e. you do not recoat your boat every year.

If the only problem you have with your bottom is flaking, I would not disturb or change the barrier coat that is already in place - it is apparently is doing its job, why mess it up or do anything new?

You need to remove the buildup of the old paint, you don't need to remove all traces. Roll on one or two coats of a light color ablative, then two coats of whatever color ablative bottom you want. In future seasons, only add paint when and where you can see the light color lower coat.

Do it right and seasonal prepping your bottom for launching can only take an hour or two a year.

Contact Interlux at 800-468-7589 - the official site of International and Interlux paints to resolve questions about compatibility of their paints with what you already have, see They are very helpful on the phone.

saildork 02-21-2009 02:17 PM

Last Fall, I sanded the bottom of my boat down to gelcoat, faired it and barrier coated it with West Systems epoxy. I sanded it with 80 grit, scrubbed it with a green scrub pad and soapy water, rinsed, and wiped dry with a cloth.

Using the West Marine equivalent to Interlux Fiberglass Bottomkote, I applied 2 coats of bottom paint according to the instructions. The boat has not been back in the water, but it has gotten wet from rain. For the last couple months, it has been under a carport with only the bow sticking out.

A few days ago, I noticed some flaking of the paint in the low places where the water will run before it drips off. I've never had this problem in the past when painting over existing paint, touching up, with this type paint nor with ablative.

Did I miss something in the prep? Should I have used a marine primer before applying the bottom paint? Was the paint a 'bad batch?'

Can anyone offer insights for me? At the moment, I plan to sail the boat as is until more of the paint flakes off, and then just start over.


s/v Stargazer

sailingdog 02-22-2009 07:29 AM


I think the problem may be that you sanded the epoxy before rinsing off the amine blush. Chances are pretty good that your sanding it like that drove the waxy blush into the scratches where you couldn't get to it when you washed the hull with the soap, water and scotch brite pad. Generally, you should always wash/degrease fiberglass before sanding/grinding it.

saildork 02-22-2009 10:15 AM


Thanks for your response. I'm not sure if I sanded before I washed or after, but you are probably right...I probably sanded first. Since I will be sailing this boat off the trailer, I'm not too worried about the paint-flaking from an antifoulant perspective. I will, of course, recoat at some point in the near future. Do you think I'll need to prime or do anything else unusual to reach a point where the bottom paint will adhere as it should?


sailingdog 02-22-2009 10:26 AM

Nah, just wash the hull with a good de-waxer...Fiberglass prep wash 202 from interlux would work nicely.

saildork 02-22-2009 10:45 AM

Thanks, SD. There's ice on the birdbath today so I'll de-wax another day. I appreciate your help.

sailingdog 02-22-2009 12:09 PM

Poor baby... :rolleyes: we'll have ice on the ground and on the boat here for another month if we're lucky, if we're unlucky it'll be two months. :) Glad to help. Post photos of your boat when you can. :)

Originally Posted by saildork (Post 453102)
Thanks, SD. There's ice on the birdbath today so I'll de-wax another day. I appreciate your help.

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