Thin gelcoat on the hull

[preserved_killick]

I have removed all the previous bottom paint (VC17) and the hull is ready for a new fresh coat. We've decided on Petit Hydrocoat based on the water based formula, price and found it to work well on a friend's boat under similar conditions.

The hull looks pretty good overall, I think, except for a few places where the gelcoat is worn thin. In a few places it appears to be sanded off and you can see the underlying fiberglass, in other places it's very thin. Before I paint, is there something I should do to cover the exposed fiberglass? I had in mind to do nothing, that the gelcoat isn't doing much at this point. I'm not interested in a barrier coat. Short of a few thick layers of epoxy, nothing much I put on will add much in the way of protection, or stop water intrusion.

I don't want to be removing bottom paint any time soon, so please fill me in if I'm missing something!

PS. For all those in New England, isn't this great weather to get boat stuff done!

-jeff

[Oscar]

I would spot mitigate the thin/bald spots with gelcoat or epoxy. Brush it on thick a few times then sand until smooth. Raw hull WILL absorb water=blisters=bad.

[Dharma]

I just finished sandind the bottom of my A30 and I noticed some thin gelcoat spots too. I really think about a barrier coat but I'm wondering why a lot of people are "against" it? The hull is dry and I want it to stay dry so why I shouldn't put a barrier (epoxy) coat?

Gelcoat blister are not a big problem up here since the boats are on the hard 8 month a year, but still....

[Ryan]

Keep in mind that thick or thin, gel coat isn't much of a moisture barrier anyway. An A30 is a relatively old boat and if you don't have blisters at this point, I believe the chances of them forming at all are relatively slim, particularly with the cold water and long time off season on the hard. Likewise, unless the boat has been out of the water a really long time, the hull likely isn't as dry as you think and a barrier coat could well trap whatever moisture is currently in the hull causing problems that you otherwise wouldn't (and so far haven't) have had.

Take my opinion for what it is, just an opinion. But it is an opinion formed over time researching and corresponding with people I consider experts, while at the same time dealing with a pretty severe blister problem on a current boat. The bottom line, at least from my point of view with regards to your boat is don't fix it if it isn't broken!

[Duncan]

The hull looks pretty good overall, I think, except for a few places where the gelcoat is worn thin. In a few places it appears to be sanded off and you can see the underlying fiberglass, in other places it's very thin. Before I paint, is there something I should do to cover the exposed fiberglass? I had in mind to do nothing, that the gelcoat isn't doing much at this point. I'm not interested in a barrier coat. Short of a few thick layers of epoxy, nothing much I put on will add much in the way of protection, or stop water intrusion.

If it was my boat, I would do as you mention. Apply a few coats of epoxy (in the thin/bare spots), to add a protective layer.

You could try to replace the gelcoat (i.e. use polyester), but I believe that's an inferior finish vs. epoxy. It won't adhere as well, and it's more permeable than epoxy.

I believe that the gelcoat was intended to be a layer between the fiberglass and the bottom paint. This "makes sense" to me, since I have never heard of a hull where bare fiberglass was left as an exterior finish.

Better check if your Petit Hydrocoat will stick to epoxy, though - I know Micron won't, so you may need a primer/intercoat.

[preserved_killick]

Dharma,

I've chosen to not put on a barrier coat based on reading through 10 years of emails from the Alberg 30 mailing list.

http://lists.alberg30.org/pipermail/pub ... erg30.org/

If you search the archive there's lots of posts on epoxy barrier coats. From what I gather, those who don't barrier coat their A30's don't get blisters, those that do..get blisters. There's examples of people barrier coating a 25 year old hull with no blister history only to get blisters the year after barrier coating.

For my boat, I didn't sand the gelcoat this thin, so I don't know how long it's been like this. Could be years.

-Jeff

[Case]

Don't worry about those raw fiberglass or thin gelcoat spots. Ignore them, only fill with epoxy if they're craters. Epoxy will not cause problems if used for fairing purposes. That's different than barrier coating which I definitely don't recommend (waste of $$ if had no problems).

My Sea Sprite 23 has raw fiberglass behind the rudder post and its been like that since new (1978). Also there's raw fiberglass at the bottom of the keel, been like that for ages - grounding removed the gelcoat there. No problems at all.

I did get blisters one year but it turned out that I had two layers of gelcoat on the keel. The outer layer had blisters. I popped them and got smooth gelcoat underneath which was a surprise to me! I spot filled the blistered areas for smoothness purposes and painted right over with Hydrocoat with zero problems. No priming or whatever, just sand the surfaces for the paint. The blisters have yet to come back.

- Case

[moonie5961]

I know that this is a very old post, but I thought I'd dredge it up as there were some conflicting opinions. Some said that raw glass will definitely absorb water and cause blistering, others said that it is not a big deal. I have some places where I was a little overzealous with the sander, and will likely have more as this project drags on- does raw fiberglass spell a recipe for disaster?

[bcooke]

It is really a fuction of the chemical properties of the resin. Resin forumulations vary and some formulations appear to be more prone to blistering than others.

Gel-coat is just polyester resin with a high dose of pigmented solids. Generally speaking, gel-coat won't protect against water infiltration much more (if any) than straight polyester resin.

When it comes to blisters and barrier coats and such, there are a ton of opinions out there. Very few concern themselves with the facts.

does raw fiberglass spell a recipe for disaster?

Not unequivocably.

[moonie5961]

Great answer, thank you!

[Commander-147]

I know that Tim's opinion is that generally barrier coat or epoxy sealing of raw glass on the hulls bottom is a waste of money. And with my own boat I have seen first hand how barrier coat caused what appeared to be blisters (which were really just in the barrier coat) because the keel was filled with open cell foam when the boat was built which had become waterlogged. The water trapped in this foam leached back out under the barrier coat and caused what appeared to be blisters. I have since removed all of that foam (with the exception of very small amounts of it under the lead in the keel) which should stop that from happening in the future. The previous owner had the barrier coat put on because the yard doing his bottom work had sanded through the gel coat and the bottom of the keel was raw glass.

Because of the situation I have described above I have searched repeatedly for the reasons behind Tim's opinion but always unsuccessfully. Because I have some large areas of the keel that are raw fiberglass I would like very much to understand his reasoning behind his opinion so I can decide if the same is true here in tropical Florida. Can someone point me to his posts where he says why he believes what he does?

Also for additional information my boat has now been out of the water for approx 1-1/2 years and will probably be out for another 9 months before it goes back in the water. With the foam gone I believe the hull is currently dry.

[moonie5961]

I wouldn't presume to be able to speak for anyone but myself, but my impression from reading just about every thread on this board that I thought dealt with barrier coats, thinning gelcoat, or blisters... is that barrier coats do sometimes have a legitimate role to play- if a boat actually HAS blisters that are either ubiquitous, or are somehow structural. Some boats are apparently prone to blistering because of initial lay-up resins, practices, etc, while others are not. As far as I am concerned, discussion at this point reaches the realm of "voodoo, hoodoo, and all kinds'a weird shit", to quote Capt. Ron. I have no idea what kind of specific lay up practices could lead to blisters down the road.

Now as for the condemnation of barrier coats. My impression is that the staunch resistance to barrier coating comes into play when people take a boat which has no blisters- and historically will not blister (like the A-30), and apply a barrier coat in the name of preventative measures. This would be bad practice because if the boat has not blistered in its 35 years so far, introducing another layer which may potentially trap moisture between just does not make sense- and may actually introduce a problem where there was none.

Good summary thread

I hope that I didn't miss anything or am not wrong in my impressions. This is just the little bit that has stuck to my brain as I have muddled through forum after forum in search of enlightenment, I am by no means educated or qualified to dish out advice, so please do not take this as the gospel. If I'm wrong, please correct me!

When it comes to blisters and barrier coats and such, there are a ton of opinions out there. Very few concern themselves with the facts.