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Old 06-06-2024, 22:08   #1
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Dry hull before barrier coating?

We discovered maybe 30 or so blisters on the narrow keel portion of our Westsail 32's hull when we hauled out, and after removing the bottom paint and very old epoxy barrier coat down to the gelcoat. They are all on one side of the boat. The other side is relatively blister free -- so whatever they did the day they laid up that half of the hull probably made it more susceptible to blisters.

The thing is, most of these blisters were very deep -- maybe 3/8" o 1/2" into the laminate. And I think that might be relevant to the question I have about hull-drying and implications to a barrier coat.

Everything I have read has said it's a waste of time to barrier coat a hull that has not completely dried, as trapped moisture will just cause blistering again. What is the mechanism here? For the blisters we have, it seems moisture has navigated its way into resin-rich areas or voids deep in our laminate, and osmotic forces have slowly pushed the laminate layers apart further, thus forming the blister. But, if some moisture is trapped, and the bilge-side and outer side of the laminate are sealed with epoxy, how would new blisters form given the supply of exterior water would be cut-off? Is it that moisture trapped in the laminate is sufficient in quantity to be drawn into these voids and form new blisters? I assumed the osmotic forces would be much lower in this scenario than an unsealed boat. It also seems like not barrier coating is a sure way to get blisters to return, as more moisture will be drawn into the hull.

I ask because we are now faced with having to make a decision about how to proceed. We've been out almost 3 weeks, but lay rates go up from $1.5 to $2.0 and then to $3.0/ft/day for the 1st, 2nd and 3rd month, and we're being charged at a 40ft-rate owing to our bowsprit and boomkin. It's not tenable for us to be hauled out much longer, and there aren't better yard rates around here.

Our next haul-out will probably be in Mexico, but at that point our boat will be our home, and we won't be excited at all about hauling out for a 3-month period. We're experimenting with ways to accelerate drying the hull out, but nothing is a sure thing.
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Old 07-06-2024, 02:46   #2
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Re: Dry hull before barrier coating?

I can understand your problem regarding "lay rates". But you are not alone with your osmosis problem.

Have you read this article

https://moisturemeters.com.au/blogs/...-boat-surveyor
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Old 07-06-2024, 07:55   #3
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Re: Dry hull before barrier coating?

That seems to support my suspicion that the moisture gets driven in from the surrounding wet laminate to continue to grow the blister.

I guess then I need to determine whether the rate at which blisters are forming on the boat is slow enough that it might not matter one way or the other. It is a 40 year old boat, and these are the only blisters that have ever shown up, other than 2-3 the PO repaired a long time ago.

So, barrier coat -- yes, it might trap moisture and new blisters may continue to form at a slow rate requiring attention in another 10 years. Or, no barrier coat -- yes more moisture may get drawn in to the laminate, and blisters may continue to form at a slightly faster rate (?) requiring attention in another 10 years.

There did seem to be an epoxy barrier coat on the boat, but I think it was applied a very long time ago, and the adhesion wasn't very good given how relatively easy it was for us to remove. Perhaps one reason the blisters were only forming in this keel region (other than there being more defects in the laminate here) -- around our encapsulated ballast and bilge -- is because moisture was coming from the inside of the boat.
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Old 07-06-2024, 09:04   #4
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Re: Dry hull before barrier coating?

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Originally Posted by Ryban View Post
That seems to support my suspicion that the moisture gets driven in from the surrounding wet laminate to continue to grow the blister.

I guess then I need to determine whether the rate at which blisters are forming on the boat is slow enough that it might not matter one way or the other. It is a 40 year old boat, and these are the only blisters that have ever shown up, other than 2-3 the PO repaired a long time ago.

So, barrier coat -- yes, it might trap moisture and new blisters may continue to form at a slow rate requiring attention in another 10 years. Or, no barrier coat -- yes more moisture may get drawn in to the laminate, and blisters may continue to form at a slightly faster rate (?) requiring attention in another 10 years.

There did seem to be an epoxy barrier coat on the boat, but I think it was applied a very long time ago, and the adhesion wasn't very good given how relatively easy it was for us to remove. Perhaps one reason the blisters were only forming in this keel region (other than there being more defects in the laminate here) -- around our encapsulated ballast and bilge -- is because moisture was coming from the inside of the boat.
I had this issue with deep blisters. I left it to dry for a couple of months and they finally stopped weeping. They were not weeping that much after the first week or two though. But that's the dilemma. SOmetimes moving the boat in the yard to a storage area is cheaper. Does your yard have a boat storage area?
There's only so much you can do though.

The other option which I have not done myself is to get a small AC unit, tent it to the blister area by taping a plastic "tent" to the hull. Allow one exit hole near the hull surface for the cold dry air to get out. The AC will dry it out fast.
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Old 07-06-2024, 09:13   #5
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Re: Dry hull before barrier coating?

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SOmetimes moving the boat in the yard to a storage area is cheaper. Does your yard have a boat storage area?
There's only so much you can do though.

The other option which I have not done myself is to get a small AC unit, tent it to the blister area by taping a plastic "tent" to the hull. Allow one exit hole near the hull surface for the cold dry air to get out. The AC will dry it out fast.
Nah, no storage around here. Really makes you jealous when you see people on YouTube doing 6-month haul-outs when it would cost us a small fortune to do something like that around here.

I've considered the tenting option using heat and a dehumidifier. But we'll be paying $560/week pretty soon just to be out of the water so I might have to just do what we can and go.
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Old 07-06-2024, 09:47   #6
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Re: Dry hull before barrier coating?

This is fundamentally a question of - How many times do you want to relive this in the future?

We can all understand the time pressure vs. $$$ factor, however, I’m sure you know that doesn’t always equate to sound decision-making as drying out a 40 yr old hull is an indefinite process. And assigning a time in the absence of consideration of the ambient temperature and humidity during which the boat is laid up is dubious.

You won’t like the following:
The advice I’ve been given by people I consider experts in dealing with this issue is simple - strip the hull.
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Old 07-06-2024, 09:57   #7
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Re: Dry hull before barrier coating?

Yeah we'd be better off selling the boat and starting over if we're signing up for stripping the hull and laying it up for months.

I think the reality is that, if we proceed with repairs and slap a barrier coat on now, that we will maybe have to strip it all off in 5-10 years, or maybe earlier. But in any case, we will plan to have the boat hauled somewhere much more affordable and also in a location where the hull can be soda blasted. Or even in the worst case, it all fails in a year or two, we should be in Mexico then and can deal with it more easily.

It is a localized section of the keel, a small 2-foot high strip at the bottom, on one side of the boat. No other part of the boat has blisters after 40 years in the water. So it's also possible that the majority of the new bottom job will last the rest of the life of the boat, and future work will be confined to re-doing that small section. So we could spend $5K+ now (storage + work and tools to strip and dry), and still not be sure the hull is completely dry, or maybe $2K in a few years to fix it if our decision doesn't pay off.
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Old 07-06-2024, 12:38   #8
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Re: Dry hull before barrier coating?

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Yeah we'd be better off selling the boat and starting over if we're signing up for stripping the hull and laying it up for months.

I think the reality is that, if we proceed with repairs and slap a barrier coat on now, that we will maybe have to strip it all off in 5-10 years, or maybe earlier. But in any case, we will plan to have the boat hauled somewhere much more affordable and also in a location where the hull can be soda blasted. Or even in the worst case, it all fails in a year or two, we should be in Mexico then and can deal with it more easily.

It is a localized section of the keel, a small 2-foot high strip at the bottom, on one side of the boat. No other part of the boat has blisters after 40 years in the water. So it's also possible that the majority of the new bottom job will last the rest of the life of the boat, and future work will be confined to re-doing that small section. So we could spend $5K+ now (storage + work and tools to strip and dry), and still not be sure the hull is completely dry, or maybe $2K in a few years to fix it if our decision doesn't pay off.
That answers my question about how often you want to relive the problem.although I’m not sure it (or anything) will be cheaper in a few years.
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Old 07-06-2024, 13:29   #9
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Re: Dry hull before barrier coating?

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That answers my question about how often you want to relive the problem.although Iím not sure it (or anything) will be cheaper in a few years.
It will be cheaper if we can plan ahead knowing the type of work we need to do. Even within California, there are far cheaper boatyards that also allow soda blasting. Up here, not so much.

But more importantly out of the country, things are of course quite different. I think in Grenada I spent less than $1500 for 3 months.
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Old 07-06-2024, 15:42   #10
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Re: Dry hull before barrier coating?

Been there, done that. Blisters are due to moisture that migrates thru the polyester resin that was used in boat construction prior to the late 90's. Putting it simply, the hull has to be dry, 5-10% moisture, as shown on a moisture meter. If you are in a humid climate that will be tough to achieve. The blisters must be first opened to dry. This is done by either spot grinding or peeling if they are pervasive. If peeled, then depending on the depth of the peel, vynlester resined matt is layed up on the hull and long board faired. Several coats of Barrier coat are then applied. I recommend Sherwin - Williams as Interprotect 2000 has been known to fail after 5 years and then promote blistering. The key is if you don't dry the hull the blisters will continue to grow, particularly in warm water since water expends when heated. JMHO
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Old 07-06-2024, 17:12   #11
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Re: Dry hull before barrier coating?

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Originally Posted by Ryban View Post
It will be cheaper if we can plan ahead knowing the type of work we need to do. Even within California, there are far cheaper boatyards that also allow soda blasting. Up here, not so much.

But more importantly out of the country, things are of course quite different. I think in Grenada I spent less than $1500 for 3 months.
Never understood why people waste other peopleís time by asking for input to a decision they already made.
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Old 07-06-2024, 18:44   #12
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Re: Dry hull before barrier coating?

I have not heard of a boat that has sunk due to blisters. And your blisters are confined to a small area. If it was my boat I would epoxy coat and launch, then watch to see if and when it needs more attention. There's not much down side to waiting.
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Old 08-06-2024, 09:40   #13
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Re: Dry hull before barrier coating?

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Never understood why people waste other peopleís time by asking for input to a decision they already made.
Iím sorry if I offended you. I was mostly trying to understand why the hull needs to be really dry from the standpoint of new blister formation and I got the answer to that question, and u appreciate all the feedback.

But It was never on the table for us to spend 3 months drying the boat out where we currently are located.
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Old 08-06-2024, 10:35   #14
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Re: Dry hull before barrier coating?

Three options:

Leave the boat on the hard for about three months to dry out the hull before barrier coating.

Haul the boat and barrier coat the "wet" hull and be done with it.

Barrier coat the "wet" hull with the intention of hauling the boat (current or future owner) sanding off the barrier coat, drying the hull for several months, and then barrier coating the dry hull.

End of story.
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Old 08-06-2024, 11:14   #15
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Re: Dry hull before barrier coating?

Fourth option: Do nothing and go sailing. Blisters never sank a boat, and they won't affect the outcome even if you are gonna be racing your Wetsnail.
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