Blistering AFTER barrier coat application!

[pir8ped]

Hi,

I have a 15 year old foam sandwich catamaran, the laminate being glass/polyester resin. After extensive renovations on the boat, I decided to apply an epoxy barrier coat to the hull followed by Coppercoat.

Originally, the boat had very few blisters, and a moisture meter showed the hulls were pretty much dry. I had wet areas to deal with on the topside and deck, so I am familiar with what the readings of my (Tramex) meter mean.

I sanded the gel coat with 80 grit paper, washed it with water and then acetone, and then applied 4 coats of Leigh's Epigrip L524. I applied the Coppercoat and sailed south from the UK, and I'm now in the Caribbean. I first noticed blistering in the Canaries, and it is now extensive.

I haven't yet taken the boat out of the water, but chiselled away some blisters and found the gel coat coming away from the laminate (most blisters 2-3mm diameter, but some 10-15mm).

I'm puzzled - the hull originally had no blisters. Now after coating with epoxy, the boat is riddled with blisters. I used the same paint as an undercoat on the topsides and deck, and there are no problems there - it is very tough and resistant to abrasion.

Any suggestions as to what has gone wrong and how to fix it? I'd like some idea before I take it out of the water again.

Thanks,

John

[Orion Jim]

I read in another forum that your barrier coat was formulated for steal hulls. I'd contact Leigh paints in the UK and see what their recommended application is. Good luck.

[minaret]

Yep, definitely formulated for commercial use on steel boats or docks and piers. Remove it, dry the hull, and do a proper 2000e job.

[pir8ped]

I saw the paint at a surplus store. It was still within its use-by date.

Before I bought it, I did contact Leigh's to ask about its suitability as a barrier coat on a fibreglass boat. I was told it was suitable, and sent the specifications they recommended for how many coats and how to apply them:

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The best option to use Epigrip L524 in this instance would be as follows:

Preparation: Clean, degrease and abrade areas to be coated
1st coat: Epigrip L425 @ 50 microns d.f.t.
2nd coat: Epigrip L524 @ 85 microns d.f.t.
3rd coat: Epigrip L524 @ 85 microns d.f.t.
4th coat: Epigrip L524 @ 85 microns d.f.t.

All above thickness' refer to application by brush.

However, if L425 is not to be used, the specification would be as follows:

Preparation: Clean, degrease and abrade areas to be coated
1st coat: Epigrip L524 @ 85 microns d.f.t.
2nd coat: Epigrip L524 @ 85 microns d.f.t.
3rd coat: Epigrip L524 @ 85 microns d.f.t.

All above thickness' refer to application by brush.

Epigrip L425 and L524 are to be applied wet-on-dry, with the overcoating times on the data sheet followed.

Regards,

A

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I'm thinking you must be right though - something wrong with the paint.

[Kevin84]

Shot in the dark here, chemical reaction between the polyester resin in your hull and the epoxy barrier coat? What kind of blisters? Osmotic?

Sent from my SPH-L710 using Cruisers Sailing Forum mobile app

[pir8ped]

I think you might be right about a chemical reaction between the epoxy and the gel coat.

I am currently making arrangements for a haul out and tracking down gel coat stripping equipment - so I should know a lot more in a few days time.

Aren't all blisters under the waterline osmotic? If there isn't air in the blisters, it will be surely water with solutes in it, and hence, osmosis?

[robert sailor]

My kick at the can is you went from cold water to warm water and your hull was not as dry as you thought. I have seen this happen many times, 20 year old boats come out of the Northern climes never having had a blister and spend some time in warm water and out they come.

[noelex 77]

Sorry to hear about your problem.

The move to warmer water was probably a major factor.

An epoxy barrier coat can sometimes make the situation worse if there is any moisture in the hull. The barrier acts both ways.
Moisture readings are not foolproof, and tend to be an relative guide rather than an absolute reading. The "few blisters" suggest the hull did have some moisture.

[exMaggieDrum]

I'm not an expert on blisters and bottom jobs but I did have it done for my boat a few years ago. It had minor blisters but I had an opportunity to have it done inexpensively (traded hours for hours for my electrical skills - I think I got the better of the deal). Anyway, the old gelcoat was ground down to the fiberglass. Noted blisters were ground down a few layers several inches around the visible wet spots. Then the boat was re-tented and left for 6 months. This was to allow moisture that was under the gelcoat to dry out as much as possible. The guy who did the job had done a few hundred other boats so I think he knew what he was doing. This was at a humid location so I think the length of time would depend on the ambient humidity. The issue is that the moisture is not overall but in spots. And they are not always obvious so a random check of the hull probably would not find all the wet spots. So (in speculation) a drying period might have made a difference.

[boatpoker]

Originally Posted by robert sailor

My kick at the can is you went from cold water to warm water and your hull was not as dry as you thought. I have seen this happen many times, 20 year old boats come out of the Northern climes never having had a blister and spend some time in warm water and out they come.

I agree, I see a lot of failed epoxy jobs on older bottoms. If you don't strip the gelcoat and let the laminate dry out all you have done is trap moisture inside. So now it's got to get out and surprise .... Blisters !

A one off moisture measurement is not enough. Once a boat is out of the water it should be metered and then metered weekly until the numbers stop dropping. That does not mean it's dry, it just means it's as dry as it's going to get in that environment.
Osmosis Testing , Moisture Meter Mythology

[donradcliffe]

It would be worthwhile to open up one of the larger blisters to see whether the fluid inside smelled like styrene or like epoxy. Welcome to the tropics!

[smj]

Don't think this is your problem, but we had Coppercoat on our old Solaris Sunstar catamaran. The gelcoat and laminate around the grounding plate were severely blistered and pitted. Didn't affect the rest of the boat though. I remember another multi had severe problems with Coppercoat.

[pir8ped]

I'm out the water. Funny how the blisters seem smaller and less common than when I saw them through my diving mask.

Anyway, the bigger blisters are full of water that doesn't smell of much at all, though I didn't fancy tasting it. And when I pop a blister off, I see the laminate, so clearly the moisture is behind the gel coat and osmosis is providing the pressure to make the blisters.

Readings on my Tramex moisture meter are high below the waterline - 20-25 on the top scale. Before I epoxied it, it read 5 almost everywhere, and close to 20 in a couple of spots.

For reference, I checked another boat nearby that had Coppercoat on it, and the readings there were 5, so it seems Coppercoat doesn't affect meter readings.

Now, where to find a gel coat peeler in Antigua??