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

[Bowdrie]

Originally Posted by capt jgw

They cheaped it up after the oil crisis of 1973 and vinylester hadn't come along yet. Polyester IS permeable,

It wasn't so much of a "cheapening it up" as directives issued by the EPA concerning allowable VOC content.
Polyester resin, (before the "troubles",) was a HIGH VOC product, with lots of Styrene in it.
Much of hull laminations consist of alternating layers of mat and roving.
The mat, being random orientated short strands needs something to hold it together, it uses a "binder".
The binder is dissolved by the Styrene and allows the resin to thoroughly coat the strands of glass, and bond to them.
When the VOCs were lowered, (Styrene content,) the mat became much harder to "wet-out", and at the microscopic level a lot of strands retained their coating of binder.
When water got into the laminate it WOULD dissolve the binder and wick along the strands that did not have a secure resin bond.
I took a while for the glass/resin companies to analyze the problems and make changes to the products to allow easier wet-out/saturation of the glass.
It was not a new thing, the Uniflite boats in the '60s were using a fire-retardant resin and were very suseptical to blistering.
Also, with most boats having no waterproof coating inside the hulls, it was only a matter of time before bilge water started finding some pathways into the laminate.
Their have been lots of studies purporting that the majority of blister problems originate from the inside of the hull.

[boatpoker]

Polyester resin is definitley hygroscopic.
Polyester resin reaches water saturation at approximately 1.5%
This does not mean your boat will ever see blisters, many have not for 50years.
Blisters and hydrolysis delamination require other factors to become an issue.

A few thoughts (opinions) on the issue ... http://www.pcmarinesurveys.com/Osmosis%20testing.htm

[Celestialsailor]

Originally Posted by 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

NO! and many threads with fiberglass repair ppl and also surveyors have said no.

This is why there are epoxy barrier coatings.

[guyrj33]

Originally Posted by 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

Definitively polyester gel coat is not impervious to water. Especially 30 year old gel coat.

[captrick2011]

Short answer no

[sand6000]

If in doubt if it is polyester (most likely) or epoxy (not likely) then sand the gelcoat and smell it. Polyester has a sweet smell.

[Rumrace]

Nope gel coat not water proof for ever. Fibreglass sure isnt. I have a Jeanneau 2017. Apparently we brag about our dual layers of Vinylester coating and Kevlar roving in key places to prevent glazing or cracking. I never do but I’ve heard it’s popular to run it in.
If the got pox and was drilled filled and skinned in Systems West it’s perfect for bottom paint no worries.
And please quit bragging about Jeanneau vinyl babies

[GreenHeaven]

well i scraped of a section of the antifoul. There is a dark layer on the white gelcoat. could that be the epoxy barrier?
Now that i scraped some of the off, how do i redo it for a small area with antifoul all around it?

[Rumrace]

Epoxy doesn’t scrap off easy. Takes chucks with it. If you have removed some barrier buy the two small cans of Systems West and do one pump mix and skim the area you’ve exposed. Is sounds like barrier primer though not Epoxy. You grind Epoxy scrap paint

[Rumrace]

No paint stick well to anything but itself. Fibreglass bottom paint take a sticky primer to bond to the hull. It’s yet another fragile lamination

[GreenHeaven]

7.2. The old blowtorch method: effective but dangerous.
An exception to the above is the old blowtorch method,
which when used with skill provided easy removal of gel coat
and degraded top laminates.
Simultaneously styrene and acids were burned out and
most of the uncured polyester cured.

Re-laminated with normal polyester and coated with gel
coat or polyurethane, hulls treated in this manner seldom
blister again.
The heat may cause deformations of the hull, loosen inside
fittings and cause de-laminations in the FRP.
There is also a risk to set the hull and the premises on fire.


Because of such hazards the blowtorch has hardly been
used in the last 20 years.

[Ramona]

It's best to treat old fibreglass hull like wood hulls. Use the same special purpose grey primers under the antifoul. Just follow the directions on the can. You can use epoxy barrier coats but it will have the same effect as an oil based aluminium particle primer just cost a lot more.

[Celestialsailor]

Originally Posted by GreenHeaven

7.2. The old blowtorch method: effective but dangerous.
An exception to the above is the old blowtorch method,
which when used with skill provided easy removal of gel coat
and degraded top laminates.
Simultaneously styrene and acids were burned out and
most of the uncured polyester cured.

Re-laminated with normal polyester and coated with gel
coat or polyurethane, hulls treated in this manner seldom
blister again.
The heat may cause deformations of the hull, loosen inside
fittings and cause de-laminations in the FRP.
There is also a risk to set the hull and the premises on fire.


Because of such hazards the blowtorch has hardly been
used in the last 20 years.

Ya...you go ahead and use a blow torch on your boat. Hasn't been done for the last 20 years? Hmmm...I wonder why. Sounds like a wives tale to me. I have been restoring and building sailboats for well over 40 years. Not once have I seen or even heard this being done.

[Rumrace]

Actually the torch method worked for me twice. The insurance company gave me solid money for the boats.
The first one took out a slip row and 35boats. If we see a guy in the boat yard with a torch who’s not a mechanic they are told to leave the club. Fibreglass burns like a flare.
Fibreglass does not bond to cured fibreglass. It gets incredibly hot during curing.

[rslifkin]

Originally Posted by Rumrace

Fibreglass does not bond to cured fibreglass.

Not entirely true. It does bond, but it's only a mechanical bond, not a chemical bond. That's why repairs are often done with epoxy, even on a polyester or vinylester hull (as epoxy will form a stronger mechanical bond).