Blistered epoxy coating

[mullet]

I recently bought an early 80s boat which was painted during its original finishing with multiple layers of epoxy paint below the waterline. In some areas there is now some blistering between the original gelcoat and the epoxy coating. The boat has been out of the water for at least a year and the hull moisture readings are good. The gelcoat that has been exposed by the blistering epoxy is in good condition with no sign of osmosis.

I originally planned to treat the affected areas by recoating with International Gelshield 200, which seems to be similar to the product applied at manufacture. However, further poking around reveals a number of other spots where this obviously happened previously and where the degraded epoxy coating was simply scraped off and then antifouling was applied directly to the gelcoat. This is the case on a small proportion of the hull, maybe 1500 sq cm. So the coating on the hull is inconsistent: most is grp-gelcoat-epoxy-antifouling. Some is only grp-gelcoat-antifouling (or grp-gelcoat-air where I've removed blisters).

Do you think I should be dealing with all the areas where the epoxy is gone (newly exposed, and the areas that have been antifouled over)? Someone previously decided not to bother with treating the degraded epoxy - I don't know if this was a reasonable approach (which implies I'd be going OTT with Gelshielding the newly blistered areas), or a bodge.

Or is there something else I should be considering? I think peeling the epoxy all over would probably be an overreaction, given the small area that is affected, and the apparently decent condition of the underlying gelcoat.

 

[dankilb]

You’ll likely need to remove the antifoul to make an informed decision on how to progress. If you opt for blasting (grit/slurry) you’ll not only have the advantage of saving the time/labour, but also exposing all areas where the epoxy is degraded.

A make/model might help others advise... but if it really is epoxied from manufacture, I presume it was a custom build of some sort?

Either way, one question now is - if epoxy was deemed necessary originally - how will the unepoxied areas hold up if left alone (or just antifouled)? Presumably there was a reason it was used in the first place?

Ultimately I would consider building up the coats in any areas where the original coating has failed/been removed and then adding a few more coats (minimum 3) all over. Blasting will get you to the point where you’re ready to start this work quicker than any sanding/scraping. Good luck!

 

[CAPTAIN FANTASTIC]

Is the blistering causing a problem apart from cosmetics?

 

[mullet]

A make/model might help others advise... but if it really is epoxied from manufacture, I presume it was a custom build of some sort?

Either way, one question now is - if epoxy was deemed necessary originally - how will the unepoxied areas hold up if left alone (or just antifouled)? Presumably there was a reason it was used in the first place?

Thanks for your reply. The boat is a Twister. The hull was built by Tylers, but was sent to a different yard for finishing and internal fit out (not Uphams, where most of them were finished), and finished to the first owner's specs. He requested the epoxy coating, presumably as a waterproofing measure to reduce the eventual risk of osmosis.

Given that most of the hulls were not epoxied, and have held up reasonably (though many/most have latterly had some sort of waterproofing treatment), I'm not sure if the areas missing epoxy will suffer in the medium term. But it's because I'm not sure that I asked here.

Is the blistering causing a problem apart from cosmetics?

I'm not too precious about cosmetics below the waterline.

I don't think the blistering is causing problems at the moment. But the concern is whether leaving some of the hull epoxy coated, and some of it just exposed gel coat (with anitfouling) might cause bigger problems in the longer term?

 

[eddystone]

My boat was epoxied from new (1987) and then re-epoxied 10 years ago or less. I've patched up bits where the epoxy has rubbed off ,e.g from mooring buoy, using Gelshield without any problems. As you probably know Gelshield needs multiple coats to be applied which is extremely fiddly in small areas and each coat needs to be fully dry before overcoating, otherwise you get small blisters from solvent entrapment, either between the epoxy and the gelcoat or between the layers of Gelshield. TBH I've done some bits quite badly by feathering epoxy over existing anti-fouling but doesn't seem to have had adverse effects.

 

[dankilb]

Fair enough. Doesn’t sound like leaving them alone and getting on with something else will do much harm.

But you mentioned being out of the water for a while and the hull being dry. So you’ve got to weigh up whether you’d regret not taking advantage of that and refreshing the epoxy treatment? Then again, that’s going to take time (especially with blasting) and/or money (...even more with blasting!) so you might also rather regret going for it once in the midst of all that.

We were in a similar position, as the boat was dry after 6-odd years out of the water (under previously ownership!) and in the end we went for blasting and will epoxy coat in the spring. At least it’ll be done. And the getcoat was shot with lots of old/dry blisters and voids only revealed by blasting.

 

[Concerto]

Tylers were known for using gel coat on the top sides and just resin below the waterline. Does your Twister have this?

 

[Keith 66]

Tylers were known for using gel coat on the top sides and just resin below the waterline. Does your Twister have this?

This would have been Clear gelcoat (most likely isothalic) NOT resin, clear gelcoat was often used below the waterline as it is far more waterproof & resistant to osmosis. No builders used just resin.

 

[mullet]

Thanks for all the replies. As far as I know (I can't access the build documentation) the hull was manufactured with a normal polyester gelcoat, not an epoxy one. It is white, which seems to support this.

Fair enough. Doesn’t sound like leaving them alone and getting on with something else will do much harm.

I'm leaning towards this - just antifouling and going sailing. In the short to medium term, how much harm could the gelcoat come to by some spots not being overcoated with epoxy?

If it starts to look like it is needed I can deal with it in a more involved way down the line. The boat will be out of the water every winter (with easy shed access), so drying the hull out sufficiently to remove and recoat the epoxy (or coppercoat instead) should not be a major pain.