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cas8100 04-17-2008 11:18 AM

Paint Build-up or Barrier Coat?
4 Attachment(s)
I have a 1988 Catalina 22 with an unknown history of bottom paint. It had an ablative-type bottom paint and I've begun the sanding process but am not sure how far to go... Does anyone know how to tell the difference between paint build-up and a barrier coat?

I have no idea if this boat has ever had a barrier coat and don't want to inadvertantly sand too far if one is already there. I've attached 4 pictures showing the current conditions.

The first is what looks to be an old repair showing its age.
The second is of the spider cracks that can be found in some areas on the bottom. I'm not sure if these are cracks in a paint build-up or cracks in a barrier coat.
The third is where the bootstripe meets the bottom coating. The white is where the bare gel has come through.
Finally, picture four is another representative of the types of cracks I find on the bottom.

My question is two-fold - does anyone know if if this is a barrier coat or just paint buildup and what should I do about it before painting with Micron Extra. I've been contemplating the laborous job of sanding the entire hull to bare gel coat, filling it, and applying a new barrier. Any thoughts??? Thanks!

DrB 04-17-2008 11:31 AM

Barrier Coat/Paint Cracks
I can't really get a good idea of what's going on from your pictures, but I believe Barrier coat is dark grey. It should always be applied to the hull before any bottom paint is applied. If applied right, barrier coat really shouldn't slough off in chunks.

I can't really tell if you have barrier coat or not, but an easy test is to take a pocket knife and gently scrape off bottom paint until you get to the hull, if you come to a hard, dark grey coating just before the hull, it's probably barrier coat. I haven't seen regular bottom paint grey in color.

Others will probably have a better test, but that's what I do.


TrueBlue 04-17-2008 11:45 AM

Just as a clarification to your post re: color, Interlux Interprotect 3000 has always been produced in a white color. Interprotect 2000 is grey, but has recently introduced a white option.

I don't have lots of experience with barrier coats, but on my last boat - Interprotect 3000 was sprayed on the repaired hull. The final effect was a very hard and smooth, white epoxy - simulating a dull finish gel coat.

I do believe that most, if not all, epoxy barrier coats are distinguished by these similar characteristics, in contrast to anti-fouling paints. The surface is very hard, unlike the flaky layers shown in your photos. Be careful sanding however, if you're too aggressive, it's easy to sand through the epoxy.

sailingfool 04-17-2008 12:14 PM

54 Attachment(s)
Also VC Tar barrier coat is black.

If you don't have any evidence of blisters, I would not bother with a bottom coat unless you intend to fully strip the bottom and just want to be conservative and bottom coat - figure 4-8 work days if you want to take that on. I would not bother.

Sand the existing paint until everything lose or flaky is gone, touch up any bare spots with bottom paint, roll on one coat, and get the boat in the water...

Pub911 04-17-2008 12:19 PM

I took a look at the pics. It looks like my boat. I keep doing what the post above says. Scrape the flakes, sand the edges and slop on ablative antifouling. It's SPRING. Go Sailing!

dakuehn 04-17-2008 12:24 PM

I think you should strip that old paint and sand. I am concerned about the cracking--that it may extend into the old gel coat and need repair. Follow the Interlux guide to the letter when going back with the Micron Extra.

DrB 04-17-2008 12:45 PM

TB and SF,

Good information re: Barrier Coat colors. I knew that if I said Barrier Coat was grey, someone with more experience would chime in with another color(s). The BC on my boat is gray and anytime I have seen others do it (limited) it was gray.

Thanks for the correction.


cas8100 04-17-2008 02:41 PM

Thanks for the replies all. I don't think its a barrier coat, just years and years of old paint. The deepest layer before the gel coat is green and it comes off pretty easily at the waterline. Now to decide how far to go... Having a barrier coat would be pretty nice...

sailingdog 04-17-2008 03:17 PM


I'd strip to the gelcoat for a few reasons. First, it'll let you see what kind of shape the gelcoat and hull is in. Second, it'll let you barrier coat the boat. Third, it'll get rid of a lot of excess weight. Fourth, you won't have to worry if the paint you stuck your new bottom paint on is going to stick to the boat.

negrini 04-17-2008 11:29 PM

Barrier coat can be ordered ready to apply or be just custom buit with some epoxy, coloring and mica, making hard to identify just by color. You could apply a chemical peeler in a portion until all paint is removed, so whatever remaining is not paint. Your pictures looks rather old cracked botton paint. Afterall, you should not be concerned as blistering is very rare on boats of such size. Looks like larger boats are more prone, due to difficulties at old times, to spread the hardener smoothly on larger areas ....

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