Antifouling Over Old Barrier Coat

AJ · Post by AJ » Mon Aug 25, 2008 3:18 am

Hello all,

I’m trying to decide the best way to ensure good adhesion of my new antifouling paint to the old barrier coat.

After talking with several local sailors (Great Lakes), they have pretty much unanimously recommended that I use VC-17 for my antifouling paint. I stripped the old paint with Peelaway Marine Safety Strip II to remove the old antifouling without affecting the barrier coat. The barrier coat appears to be in good shape with only a few small chips, one along the stem and the rest located around the joint where the external ballast meets the keel.

Here’s some background info on how I got to the point where I am now:

Searching online for the best method to go about the new antifouling, I found a promising posting titled “Applying VC-17 Bottom Paint” on the website of Lake Michigan based Torresen Marine with the following instructions:

The third instance. Applying VC-17 over an epoxy barrier coat. It is not true, by the way, that VC-17 can only be applied over VC Tar. While it certainly can be, it goes on over Interprotect Epoxy barrier coats just as well. In this case apply the barrier coat according to the instructions. After applying the last coat of tar or epoxy, follow the instruction for applying the first coat of antifouling without sanding (called “hot” or “wet on wet” coating) in the case of VC Tar or Interprotect 2000E/2001E. In the case of Interprotect 3000/3001, you must let the epoxy harden and sand with 180 just as though it were a new hull. Please be sure you’re reading the correct times for applying antifouling paints (not another coat of epoxy, they’re different).
http://www.torresen.com/news/?p=3439

Further digging on the website uncovered that the instructions were first posted there in 2004 and submitted by a Great Lakes Interlux representative:

http://www.torresen.com/news/?p=480

This sounded like the way to go. I bought some Interprotect for another coat and checked the instructions on the can, which states the maximum times for overcoating with “antifouling.” It also indicated that if the barrier coat on your boat has exceeded the maximum drying time (which is a given in my case) that you would have to sand it with 80 grit and apply a new coat.

So I scuffed it up with 80 grit to give it some tooth.

Then I decided to check the Interlux website for any additional application tips. The product data sheet, dated 2004, charts the specific overcoating times for a whole list of antifouling paints… without any mention of VC-17. A separate note later on states:

When overcoating with VC 17m or VC 17m Extra allow Interprotect 2000E to dry for 24 - 36 hours, then sand with 180-220 grit sand paper.
Which now suggests there is no “hot coat” for VC-17 as the Torresen posting had discussed.

Now I’m wondering about the wisdom of rolling on a single layer of Interprotect over the hull before applying the VC-17. It also crosses my mind whether or not a single new coat of Interprotect will even bond that well with the old stuff and might end up causing more trouble than its worth. I wouldn’t want water to get between the new and old coats and cause bubbling or other problems.

Here, then, are the options I’m considering:

(1) Proceed to apply the VC-17 immediately over the 80 grit scuffed barrier coat.
(2) Spot repair the few small chips in the barrier coat with a dab of Interprotect and proceed to apply the VC-17 over the 80 grit scuffed barrier coat.
(3) Roll on one coat of Interprotect, wait 24-36 hours, sand with 180, and then apply the VC-17.
(4) Roll on the Interprotect and hot-coat the VC-17 within a few hours without sanding.

Any input would be appreciated.

AJ

Rachel · Post by **Rachel** » Mon Aug 25, 2008 9:57 am

I only have a moment here, so pardon the brief posting, but here are some notes:

1) Be sure you want VC-17, because you can ONLY overcoat with more VC-17, and if you ever want to switch paints, you have to physically remove the VC-17. That's not to say it's not a great paint, just be sure you're not about to move to salt-water, etc.

2) Everything I've read says that you cannot hot coat with VC-17 on top of barrier coat, but instead need to wait for it to dry, and then sand. This makes sense, since VC-17 is a vinyl paint, and isn't in the same chemical "family" as epoxy-type products.

3) My boat has an Interprotect 2000 barrier coat base and then VC-17 over it (done by previous owner). I removed a 2' x 2' square of VC-17 by sanding (thinking about removing it all and wanted to get an idea of the time it would take), and I can clearly see that the Interprotect was sanded for "tooth." The VC-17 is well-bonded.

Rachel