Once and for all, does the gel coat under the antifoul keep the water out or not???

[GreenHeaven]

I cant get a straight answer anywhere...
Yes, no, depends...

its a 30yo gel coat. Its probably polyester so does it absorb water over time?
Does antifoul let water through it

Is gel coat Impermeable?
impermeable surface means any surface which does not permit fluids to pass through or penetrate its pores

[ThereAndBack]

I'm not an expert, so take this with a grain of salt. It is just one data point.

I owned a fiberglass boat that was gelcoated below the waterline and then had bottom paint put over that. Blisters developed on the bottom between the gelcoat and the fiberglass.

The boat was built in 1972 and I am unsure of the resin used in the gelcoat.

[goboatingnow]

Gel coat , ie polyester is not waterproof , it allows a certain amount to seep into the laminate.

[GreenHeaven]

There are no blisters. The boat was built in mid 90s. It was a top of the line boat so im sure they used quality products. Jeanneau. Im just not sure if its polyester or epoxy gell coat. I assume polyester.
Is there anyway to determine what the gel coat is made of underneath the old antifoul, and how impermeable it is?

But isnt antifoul impermeable?

[capt jgw]

Originally Posted by ThereAndBack

I'm not an expert, so take this with a grain of salt. It is just one data point.

I owned a fiberglass boat that was gelcoated below the waterline and then had bottom paint put over that. Blisters developed on the bottom between the gelcoat and the fiberglass.

The boat was built in 1972 and I am unsure of the resin used in the gelcoat.

That boat was probably better quality resin than used in the late '70's and '80's. They cheaped it up after the oil crisis of 1973 and vinylester hadn't come along yet. Polyester IS permeable, vinylester less so and epoxy less than that. Very few production boats use epoxy, that's why aftermarket epoxy barrier coats are popular. And most antifouling is also permeable, that's how it works. The copper leaches out over time and kills or repels growth.

[S/V Illusion]

There is no vagaries here. Don’t know why you didn’t find a definitive answer.
Gelcoat is water -resistant, not waterproof. And anti fouling bottom paint is intended as neither.

[GreenHeaven]

Osmosis is a process whereby an imbalance of fear across a knowledge barrier causes money to flow from the high fear to the low fear side. A barrier coat of information can be used to block the flow and end the problem.

[SaylorMade]

Originally Posted by GreenHeaven

Osmosis is a process whereby an imbalance of fear across a knowledge barrier causes money to flow from the high fear to the low fear side. A barrier coat of information can be used to block the flow and end the problem.

Best post I've read in a long time

[Orion Jim]

Yes.
Yes.
No.

[Pegu Club]

Originally Posted by GreenHeaven

Osmosis is a process whereby an imbalance of fear across a knowledge barrier causes money to flow from the high fear to the low fear side. A barrier coat of information can be used to block the flow and end the problem.

This right here^^^

We did a barrier coat on our 1977 Bristol, we had no blisters when we scraped it down to the Gel coat, it was a fair bit of work, but if “ waterproofing” your hull is what you are after, an epoxy barrier coat is your remedy,

Fair winds,

[fstbttms]

Originally Posted by S/V Illusion

And anti fouling bottom paint is intended as neither.

In point of fact, anti fouling paint works by letting water penetrate its matrix.

[Searles]

The answer is no gelcoat is water permeable under water pressure ie afloat not getting wet on the hard ,anti fouling paint is water permeable as stated that’s how it works ,epoxy on the outher hand is about as close to water proof as you will get on a grp built boat ,the purer the better ,at least that’s how it works in Australia .⛵️⚓️

[Don C L]

Once and for all, no.

If there are no blisters, and you have no unusual leaks, there is little to cause concern.

I have a 60 year old boat with a very permeable gel coat and no blisters and various layers of bottom paint. No problems.

[contrail]

Originally Posted by Searles

The answer is no gelcoat is water permeable under water pressure ie afloat not getting wet on the hard ,anti fouling paint is water permeable as stated that’s how it works ,epoxy on the outher hand is about as close to water proof as you will get on a grp built boat ,the purer the better ,at least that’s how it works in Australia .⛵️⚓️

And, to the OP, for a 90's era Jeanneau, you are probably looking at an epoxy barrier coat applied over gelcoat, which is a principal reason there are no blisters. Let it be!

[Fore and Aft]

Green Heaven your over thinking it all. I would say Contrail is right, certainly in our yard in the 1990s we were applying epoxy barrier coats.
Can I say that to me osmosis is always a mystery. I surveyed a yacht the other day and the bow section below the waterline was osmosis free yet the rest of the hull had a section of real bad blisters and then another section of a few blisters. I surmised that when the hull was laid up the guy on the bow section was diligent in removing all the air bubbles in the wet fiberglass while his colleagues did a half job. Reminds me of another boat we repaired and in the laminate was beer bottle tops.

Cheers