Dimpled gelcoat

[Ubergeekian]

My Jouster is now 35 years old. In a few places the gelcoat is spalling off small circular flakes, about 3mm across, leaving a dimpled surface like that of a golfball. This is only happening on the topsides and doesn't seem to correspond to wetness - if anything it's happening more to bits that are, barring rain, dry - so I don't think it's osmotic.

Has anyone else encountered this? Any reason why I shouldn't just clean out the pits, fill and paint?

 

[johnlilley]

Hi there, could it be where the topsides have been previously painted or sprayed and it is this coating that is flaking off or blistering. This is quite common on older coatings where water has got between the gel coat & topcoat. More often starting close to the waterline and working upwards.
If it is paint flaking. not serious but cosmetically irritating as it usually continues to affect, as yet non, affected areas. If avoiding major effort then just fill surface & locally touch in if appropriate.
Before doing anything major, just check whether it is actual gel coat problem first just in case it is not a failing retro paint coating. There is a photo of paint blistering as against osmosis blistering on my website on the "site index" page if that helps further

John Lilley

 

[Simonpk]

I have got exactly the same on my Pageant (1975). The hull is sound with no blisters at all, mine are along the coaming just above the rubbing strake and some in the cockpit.

I ran of time to resolve it this spring, so it's a job for next Autumn. Painting the coaming will be my very last resort. I have got white Gel Coat Filler and am going to fill then wet'n'dry with very fine coarse & polish. Hopefully the results will be satisfactory

Hopefully someone else out there might have a better solution.

Regards

Simon

 

[Ubergeekian]

Hi there, could it be where the topsides have been previously painted or sprayed and it is this coating that is flaking off or blistering.

Thank for that. It's definitely a gelcoat problem: it's happening on painted and unpainted sections and the chips which come off are curved on one side - like small dried split peas.

I have got exactly the same on my Pageant (1975). The hull is sound with no blisters at all, mine are along the coaming just above the rubbing strake and some in the cockpit.

Ah-ha. Sounds like a mid-seventies Westerly habit. I must have a look on the WOA website.

 

[Avocet]

Do the affected areas correspond to those parts of the hull that get the most sunlight?

 

[alahol2]

I had a very similar problem on the cabin sole of a Vivacity 20 many moons ago. It was caused by the foam backing of a carpet being permanently wet with fresh water (rain/condensation). So, do your pimples show where eg a winter cover, fender mat, carpet covered trailer arms etc touch the hull? If so then I think you could call it a form of osmosis. Fresh water is much more aggresive than salt in the osmosis wars.

 

[Ubergeekian]

Do the affected areas correspond to those parts of the hull that get the most sunlight?

Interesting question. I think the answer is "no" - there's some on the cockpit sole (under the nonslip paint, a bit) but none on the coachroof.

I had a very similar problem on the cabin sole of a Vivacity 20 many moons ago. It was caused by the foam backing of a carpet being permanently wet with fresh water (rain/condensation). So, do your pimples show where eg a winter cover, fender mat, carpet covered trailer arms etc touch the hull? If so then I think you could call it a form of osmosis. Fresh water is much more aggresive than salt in the osmosis wars.

No, it's all on completely exposed and generally dry places ... even the cockpit sole is dry unless it's raining.

 

[Avocet]

Ok, it's just that Avocet's topside gelcoat failure was very obviously worse on the bits that got the most sunlight, so I concluded that it was triggered (or at least accelerated) by ultraviolet. When I started griding the gelcoat off, it was also pretty obvious that they started on the outside and worked in towards the laminate (i.e. about half of them disapperared before I got all the way through to the laminate).

Anyway, as it's not that...

...I dunno - sorry!

 

[TradewindSailor]

This is extremely common down here in and near the tropics.

Gelcoat is not immune to aging, and it ages faster when it gets hot or is exposed to uv and solvents. One of the ways it breaks down is that it shrinks and cracks through it's thickness .... resulting in blister like scabs. I say blister like because it was created by shrinkage not absorption of moisture.

You may have some success using a high-build epoxy primer, sanding smooth, and then painting. It's the least effort, but they may re-appear through the surface some years later.

The other route is to grind the gelcoat off completely in the effected region. I'd be rather inclined to put this off for as long as possible.