Hello everyone, I have a Prindle cat and was debating on whether to reinvest in the boat or not. The boat is solid top to bottom, front to back, but the gel coating in the heat is beginning to show blisters. The question I have is whether I can sand this down to the native fiberglass and reshoot new gel coat with a gun. Does anybody have any idea the condition of the fiberglass underneath on a boat like this?

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Mike
Chicagoland area

Prindle 16
Hobie 16, 18
Laser
Flying Juniors
Seatrend board sailor
C Scow
Prindle 15, 18, (current)
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Usually when there's blistering the fiberglass underneat the gelcoat is kind of rotten under the blisters. On a solid fiberglass boat it's not that bad to repair but on a foamcore hull that could be a challenge the skins being very thin.

I must say I never done it on a foamcore but have repaired an old laser that is solid glass.

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AB
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Palm sand it down to 150 grit and paint using Interlux Brightside (Jamestown Dist.--$35/qt), One qt for a 16. Take 3 days to paint, turning hulls on side to give a flat surface using good quality brush. Go to Sam's or Costco and buy a $12 12x16 tarp to keep sun off your boat. Pete

What pete says.

I did a fiberglass repair on my foam cored 5.7 a few weeks ago and it wasn't bad. I didn't try to replace the core but tried to preserve as much as I could while grinding the repair area. I simply treated the repair as if it was single ply fiberglass and it came out looking good and seems strong.

Coolhead, I've not seen what you describe with respect to rotten fiberglass underneath blisters (although I imagine excessive blistering could be a consequence of that). In my own experience usually delaminated or cracked glass shows itself by being pretty soft and crackly to the touch or shows right through the gel coat. Normally the blisters I've seen are a function of leaving the boat in the water for a long time (several days) and the water pinholing into the coating causing gelcoat 'acne'. Or for larger spots it could be a consequence of poor surface prep under a newer layer of paint or gelcoat causing areas to not be adhered properly.

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Dave Bonin
1981 Nacra 5.2 "Lucile"
1986 Nacra 5.7 "Belle"
Winnipeg, Manitoba, Canada
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First, what I describe happen mainly with polyester resin. Vinylester has better resistance to that as well as epoxy because they are more permeable to water. With polyester resin, water migrate in the gelcoat and resin by osmosis. Once it's there it forms an acid that eat the resin. When you repair those blisters you have to be very carefull because the acid is under pressure and it can squirt out of the blisters and end up in your eyes.

Beach catamarans don't stay in the water for long so the problem maybe just superficial but on a hull that stays in the water it can become serious.

Here's a link where you can see what I'm talking about (yes, that boat is in bad shape):https://www.youtube.com/watch?v=9T_eFVF6vOw

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AB
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All great advice everyone, the boat is solid like I say, I think it is simply a product of old age. Blisters reveal in the hot temps on the sidewalls only. I think if I take the finish down to base fiberglass, and clean and prep surface from any pooling resins and and reshoot I would be okay. Is the poly urethane the way to go these days over over gel-coat? Gel coat to me seems very porous to future staining and re-occurring problems. However, poly can scratch down and flake off under abuse.

Any added thoughts on either product?

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Mike
Chicagoland area

Prindle 16
Hobie 16, 18
Laser
Flying Juniors
Seatrend board sailor
C Scow
Prindle 15, 18, (current)
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If the blisters aren't an indicator of bad fiberglass I would hesitate to strip them all the way down. Just sand the existing gel coat to roughen and get rid of the blisters. You don't want to cut into good resin and mat if you don't have to.

I've used gelcoat with good success, mix in small batches and paint with a brush, then palm sand with a random orbit with 220 between coats to get rid of brush marks and wet sand the last coat and polish.

However if Pete says interlux brightside, then that is definitely the way to go. He's painted a quite few boats and I've only repaired mine.

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Dave Bonin
1981 Nacra 5.2 "Lucile"
1986 Nacra 5.7 "Belle"
Winnipeg, Manitoba, Canada
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