Bottom job. Ran into crazed and cracked Gel Coat

[pvtpotter]

I have provided some pictures here. My initial plan was to do a light sanding and start painting. Some of the paint was chipped so I had to sand a little more deeply and get through the base layer of paint (blue). Then deal with any barrier coating (a dreaded prep. job) next year.
Black over blue bottom paint. Under the blue, I found some serious cracking in the gel coat. So much so I was worried 3-4 coats will not water proof it enough. (Not that bottom paint is made to waterproof the underside.) A couple of spots have depressions which actually have gone through the gelcoat. They are small spots. (See the shot of the bow).
Please check out my pics and see if you have seen anything similar under your bottom paint. How did you handle it? Do you wish for a barrier coat? Can you do a partial barrier coat where the rough cracking is? I doubt it.

 

[braol]

Really the only thing to do is to sand down those gel-coat areas to the point where you can use fairing compound, barrier coat, and then bottom coat. I have areas like this where the gel coat looks 'chipped' (for lack of a better description).

The good news is that it seems that the gelcoat has seemingly flaked off, but has not blistered. Blistering would mean that our barriercoats are compromised and that water is getting in under the gelcoat. That, of course, would be very bad. What I've chosen to do is to grind/sand and do the fairing compound thing on one section of the bottom per season, rather than take on a whole bottom stripping project. Again, with an obvious lack of blisters, I don't feel that the gelcoat cracking is as big an issue as it could be (Other than slowing the boat down with a rough bottom). Splitting the bottom up into sections makes the job managable.
I'm sure that others will say that's a I'm crazy, but with no blisters it is obvious that the bottom coat is effectivly standing in place of the gelcoat. Now, I do have the advantage (although expensive) of the fact that here in Chicago I have to take my boat ot of the water every year. So I obviously do not have the boat in the water leaching bottom coat year-round and I can work on the exposed bottom a little at a time. Maybe that buys me more time, but until the bottom actually blisters it should not be an emergency situation.

 

[stollo770]

I'm going to have to disagree with Barol on the blistering part. Your bow is full of them and there are probably more lurking behind your compromised paint. You only really have one course of action: you must soda blast your hull and repaint it. Soda blasting will remove all of your paint safely and will reveal any more blistering below your water line. Then you have one of to choices: hire your marina to fix everything and repaint your hull for you (best option), or fix everything and repaint the hull yourself.

I recommend going the marina route because you cannot screw around with blistering and bottom paint. The very integrity of your hull, nay, your boat is at stake here. Fiberglass loves to absorb water, so any mistakes you make will only feed its thirst and accelerate the decay of your hull.

I was faced with a similar situation a couple months ago, but my hull did not show extreme visible damage like yours does. I chose to hire my marina to blast everything off and that revealed more blisters then stars in the sky. So I hired them to fix/repaint everything and now everything is in tip top shape. I'm good for years now, and I am completely confident with the integrity of my paint and my hull. I'm glad I hired them too, because it would have taken me months to get everything right. I also repainted my topsides, but I did that job myself because it was above the waterline, and was relatively simple compared to the bottom work.

Also, nice paint job on your topsides! I love that dark blue color and when I painted my topsides I chose it that color scheme exactly. Did you do it yourself? What paint did you use?

 

[braol]

I think those pictures of the bow are showing beaded-up water not blisters.

I have similar areas where the gelcoat was compromised by aggressive barnacle build-up followed by aggressive removal.

 

[stollo770]

The water droplets on the topside paint are not blisters, the topside paint looks amazing. However, the damage thats going on with the bottom paint is the very definition of blistering. In fact the blistering is so bad on the bow that the affected gelcoat has fallen off, leaving a massive hole. Everything under the water line needs to be blasted, and every single blister (I suspect there will be many more) needs to be filled, faired, and repainted with 4 coats of barrier, 2 coats of hard, and 2 coats of ablative. Get a good mil thickness that will last for years and prevent further hull decay. The problem with pvtpotter is quite serious, he needs to get on that before he can put his boat back in the water.

 

[pvtpotter]

I had rinsed off the sanding dust is why you see the water droplets. Guess I should have mentioned that.
She splashed on Friday with 3 coats of ablative. It's been like that for years, and I don't see any real delamination going on. The spots on the bow sure are down through the gel coat to glass. The blistering has not spread at all. Next year I will haul again, and from what @barol says, it seems I can do the barrier coat in sections which makes it seem more manageable to me, and I can spread it out over a couple of springs.
@Stollo770, have you hauled, peeled back the bottom paint and taken a view of your bottom? I wonder if yours has similar crazing and cracking of the gelcoat. Seems most people on here with our model boat have run into it.
Thanks everyone for the comments and suggestions. I'm game to hear more.
Has anyone else done their barrier coat in stages or spread out over time?

 

[Jim Legere]

I like this guy's common sense approach to blisters. Basically, there are very few cases where blisters ever pose any structural danger. Just clean 'em up and dry them out as best as you can. Apply some epoxy filler and coat with a suitable barrier coat. Then go sailing. You are on the right track.

I also believe that Hunter often applied the gelcoat too thick back in the 70s & 80s. This lead to some of the crazy hairline cracks and bits flaking off, as in your pictures. But they didn't skimp on the glass & resin - these Cherubini Hunters are built like tanks. They will outlast most of the folks on this forum...

 

[fstbttms]

Not that bottom paint is made to waterproof the underside.

Not that it matters now, but FYI- anti fouling paint is not waterproof in any way, shape or form. Quite the opposite, it is designed to allow water to penetrate. This is how the biocide is transported from within the paint matrix to the surface.