Bottom Protection

[hawkeye]

Arriba doesn't have a blister problem, but she hasn't sat in a slip before now. The previous owner slapped some on VC17, but not a barrier coat. I was told that Interlux Interprotect is easier to apply than VC tar, but there are a couple of different Interprotect systems. The gelcoat is in great condition, so I am leaning towards the Interprotect 2000. This is a freshwater boat. Opinions?

[Jason K]

I don't think an epoxy barrier coat should be applied unless a blister problem already exists. It prohibits moisture from passing into or out of the hull and can actually lead to blisters. Even if Arriba has been drysailed, it will still, probably, have wicked up some moisture. The impermeability of the barrier coat can lead to blister formation.

Why do you feel it may be necessary to apply a barrier coat?

[hawkeye]

Why do you feel it may be necessary to apply a barrier coat?

I was told to do so by a good friend.

What about tar? So your saying VC17 is all I need?

[Jason K]

My understanding is that you can apply VC 17 directly to the fiberglass. The "tar" is an epoxy type system, right?. My advice would be to apply it directly if you do not have an existing blister problem.

By the way, what kind of boat are we talking about?

EDIT: Just checked www.yachtpaint.com. There is no need to apply the tar or a barrier coat. However, it does recommend removal (ideal) or sanding through 320 for old bottom paint.

[rshowarth]

I am interested in this topic too.

The Rhodes 19 I am custodian of has an unknown bottom paint on now. I intend to strip and sand the bottom and then apply a new coat of bottom paint. This boat will be anchored in saltwater in Massachusetts for about six weeks out of the year.

Someone who owns a Rhodes 19 in the area has recommended Pettite Unepoxy and a periodic scrubbing during the season.

Do I need to put a primer on the hull?

I may also fair and paint the topsides. Does that matter as to whether to use a primer or barrier coat on the bottom? What grit sandpaper do I finish with for painting?

[Summersdawn]

I would think any older boat that hasn't developed a blister problem isn't likely to develop one in the future. Worst case scenario is a dry sailed boat might develop a handful of blister - certainly nothing to worry about.

If you are determined to apply a barrier coat, make sure it is done properly, or you will just be wasting time/money. I believe the bottom has to be stripped of all paint, and the laminate has to be totally dry. This usually involves tarping the bottom and ground under the boat, using a bit of heat, and checking the moisture content in the laminate periodically with a moisture meter. If you apply a barrier coat to a laminate that isn't dry, you have effectivly sealed that moisture in.

There are so many varied opinions as to what to do about blisters, it can be pretty confusing over what course of action to take. I'm of the opinion if it ain't broke, don't mess with it.

[dkall]

Jasons post just doesn't make an common sense to me. A barrier coat adding to the blister problem. I understand what he's saying about then water is trapped inside the coat. But if the interior isn't fully sealed then there is a way to escape and if the inside isn't fully sealed then water too can enter from the inside. At least that was the old theory. We've epoxy painted our bilge, all of it and it's a lot.

An excellent site to check out for information on blisters is: http://www.yachtsurvey.com/BlisterFail2.htm

Even after his discussion I still barrier coated our bottom. I was on the hard for 3 years and for a couple of hundred lousy bucks I figure all that I'm going to lose if money. :)

[hawkeye]

From my understanding, tar is a soft material and can damage easily. Epoxy barrier coat is easier to apply and can take more abuse. I beach Arriba frequently since she's a centerboarder, and I want this to hold up. Don't get beaching and grounding confused...one's intentional and one is not. Anyway, I don't have a blister problem, and I don't want one. I do plan on putting several coats of VC17 on instead of the one that the previous owner applied.

[Jason K]

The article dkall linked to was certainly interesting (though I'd disagree with the premise that the cost of a repair and its effectiveness are necessarily linked) and I agree that an attempt to correct a blister problem that's done incorrectly will almost certainly lead to more blisters. The article does not, however, address the prevention of blisters on boats that are unafflicted. I maintain the position, even if it may lack common sense, that an epoxy barrier coat is a function of blister repair and, if used as a preventative measure, is as likely to create blisters as it is to retard blister formation.

Water will migrate into the laminate and, if trapped there by an epoxy barrier coat, will have the ability to form blisters as it may not permeate into the bilge or other interior portions of the boat. Also, if all absorbed water can osmotically transfer to the boat's interior and evaporate, why do boats spend months on the hard "drying out."

Hawkeye, if your boat has been drysailed and hasn't absorbed much water into the laminate, then perhaps a barrier coat won't lead to blistering.

There are, obviously, two sides to the discussion. For me, though, I'll refrain from barrier coating unless it is part of a systematic blister repair program.

- Also: Interlux recommends applying two or three coats of VC 17 annually.

[Tim]

I've discussed this at length on this forum before. Jason is echoing my own thoughts on barrier coats, but if you want to read one of my previous posts on this subject, try searching for "barrier". I don't see a need to repeat myself in a new post.

Here's one thread, for example: Epoxy Barrier Coat: pros and cons

I believe in barrier coats only as part of a repair system for a boat that is previously blistered.

Note that the type of blisters that everyone is so worried about occur only in salt water, as the minerals and salts are required to set up the chemical reaction that causes the sort of acidic blistering problem that might actually be something to worry about. Small, insignificant laminate blisters that form beneath paints or between the laminate and the gelcoat are a wholly different animal, and pose little threat. These can occur in fresh or salt water.

There are two legitimate sides to this argument. One must absorb both sides and decide what makes sense to them. But there are definitely cases where boats that had never blistered before suddenly develop small blisters after a barrier coat is applied as a "preventive" measure. The blisters are between the laminate and the barrier coat. Coincidence? Or cause and effect? Even though in these cases the blisters are not of the worst, styrene-eating variety, it's still a clear example of how a barrier coat works as designed--in either direction. This may not be a good thing.

Personally, I believe the whole issue is blown far out of proportion in the mainstream boating press and so forth. It's natural for many people to believe what they are being told in article after article, ad nauseum, without really giving much thought to the processes at hand, and whether their boat is truly at risk.

Note also that in northern waters, where boats spend half the time hauled out, blistering of any sort is virtually nonexistent. One can spend lots of time and money on products and application, but why, if the problem isn't there in the first place?

[hawkeye]

You guys save me alot of time and money.