To Barrier Coat or Not to Barrier Coat

[StephenMaturin]

Esteemed sailing colleagues,

I'm buying a 1990 C&C 34+ (Balsa cored hull). The bottom paint, though applied 9 months ago, is flaking off down to the gelcoat. Large chunks came off when pressure sprayed for the survey. Thankfully, the hull appears to be blister free and dry (per surveyor per moisture meter)!

Because there appears to be poor adhesion of the paint to the gelcoat, I was thinking of having the bottom paint stripped, applying a barrier coat, then repainting.

I got the "you've reached the end of the internet" sign after googling this question ad infinitum, so I am asking you all for your thoughts on this issue.

Here are the facts:
-1990 boat, polyester resin with kevlar/glass mat used in construction process.
-Freshwater kept until 1-2 months ago, now in saltwater
-No previous barrier coat applied
-Currently dry core in the hull (if moisture meters are to be given more credence than a high-tech divining rod).
-No visible hull blisters (though the rudder is riddled with them)
-I do not intend to let the boat sit and dry out. I want to sail it, now.

Here are the questions:

1. Is it worth the expense to apply a barrier coat to theoretically keep the hull blister free and the core dry?
2. Would the barrier coat actually do anything if I don't provide any drying time (more than a day or two)?
3. Is the theoretical protection of the barrier coat worth the worry that the barrier coat would not adhere well to the gelcoat or that the bottom paint would not adhere well to the barrier coat and that it'd all need to be redone?
4. Is it possible that the boat actually did develop blisters while in fresh water, which have been "dried out" now that she's been in saltwater for a few months? I'm picturing the fresh water seeping into the glass, then being drawn back out by a higher osmotic gradient while sitting in saltwater for the past few months.
5. Do I need to start researching astrophysics so that I can stop thinking about osmosis, hydrolysis, and other issues obfuscated by an industry funded by blister removal and prevention?

Thank you in advance for your consideration and help.

[mitiempo]

If the hull doesn't get a chance to dry out (months) barrier coating is a waste of time. It will keep the water in.

[Waltthesalt]

1. Questionable value as not all boats are susceptable to blister problems, that was mostly a 70's era issue. Given the age of your boat you'd have seen them by now if you have a problem. Also minor blisters if it does occur can be treated individually.
2. What mitiempo is referring to is stripping off the gelcoat and layer below and dehydrating the hull core (this takes months in a contained environment) and applying epoxy. Even then blistering may come back. More risk than gain inyour situation.
3. Need to ask the paint/barrier material manufacturer that about adherence.
4. I don't think so. What happend in blistering is water permeated then froms a larger molecule with the hull material which can't get back out. Salt water on the outside shouldn't affect what's on the inside.
5. I think the most helpful read on this is "002-650 Gelcoat Blisters: Diagnosis, Repair & Prevention" you can download it for free on West System epoxy's web site how to section. You could e-mail them and ask what the value would be in putting a coat of expoy over the gelcoat.
What I'd concern myself about with a balsa core is water intrusion in the core where there are thru hull penetrations. Your surveyor should have checked those areas.

[Minnewaska]

With the right combination of barrier and antifoulant, a primary advantage is adhesion. Which you are witnessing in real time. Whether is will help prevent blistering will never be known and I say its worth a try if it helps with adhesion anyway.

[bubb2]

fiberglass is not waterproof. you did not say if will be hauling the boat next winter. barrier-coat is a good thing especially with a cored hull. It would be better to do in the spring after a winter haul out.

[RichH]

With no evidence of 'blisters' there is no need for barrier coat. Since the boat has not 'dried-out' you can be assured that the barrier will not bond correctly and may even trap moisture (water vapor)within the hull. I'd recommend to apply barrier only when barrier is needed, not 'prophylactically'.

That the present bottom paint has lost adhesion ... quite common especially if the paint is an ablative as its quite common for 'deeper' layers of ablatives to lose adhesion after a few years .... and the result: big chips and flakes. The real way to solve that is to remove the paint, scuff up and start all over; and, if an ablative is chosen apply only the amount needed (history that you will 'develop' over time). Too much ablative paint usually leads to 'large flaking'. If you choose an ablative, suggest you apply a contrasting 'indicator color' first .... and then with your 'chosen color' over top of that; and, only paint with 'new' (differing color) at next 'haul-out', etc. when the indicator color begins to 'show through'. When no 'indicator' is showing through, a light sanding is usually all it takes to 'reactive' the ablative, sometimes not even light sanding --- your 'developed history' will dictate.

[casey1999]

Originally Posted by RichH

When no 'indicator' is showing through, a light sanding is usually all it takes to 'reactive' the ablative

Is the light sanding is somthing you do with the boat in the water (diver)?

[sailingfool]

Originally Posted by StephenMaturin

Esteemed sailing colleagues,

I'm buying a 1990 C&C 34+ (Balsa cored hull). The bottom paint, though applied 9 months ago, is flaking off down to the gelcoat. Large chunks came off when pressure sprayed for the survey. Thankfully, the hull appears to be blister free and dry (per surveyor per moisture meter)!..

So I gotta ask, how many days did the boat sit after hauling for the hull to dry before the surveyor worked it over with the moisture meter? I've alwayss heard three or four is a good minimum...

[RichH]

Originally Posted by casey1999

Is the light sanding is somthing you do with the boat in the water (diver)?

I haul at least every 12 mos. (when not 'cruising', and then every 18-24 mos.)

[WDS123]

No need to barrier coat -