Is it worth epoxying a sound GRP hull, or is it just fashion?

[MapisM]

Before storing the new to me toy, I stripped 14 years worth of antifoul from her GRP hull.
Sandblasted first, then finished by hand with fine orbit sander - a pretty good job indeed.
Now, I am considering whether to take the opportunity to give Coppercoat a try or not (leaning towards yes, but I'm not positive yet).
But before coming to that, I discussed with some "experts" whether it could also be worth epoxying the hull, which is now bone dry, for osmosis prevention.
And this opened a can of worms, so I thought to share what I heard and ask for your views/experiences on this matter.

As a premise, after sandblasting the antifoul to bare gelcoat, the hull appears in very good conditions.
Some small blisters were found along the spray rails, but according to everyone who saw the hull, they are more than likely due to microbubbles of air left between the gelcoat and the first GRP layer, back when the hull was built.
Under these bubbles, the fiberglass appears smooth and solid, with zero vinegar smell and ridiculously low humidity values, anywhere.
BUT, when discussing the "what now?" before re-antifouling the boat, I got radically different views.

The more widespread school of thought suggests to fill the blisters with an epoxy filler, and then give several hands of epoxy resin (Gelshield 200 being apparently the most popular stuff for this job).
I' not expanding on this because I believe it's a rather well known type of treatment, for both osmosis cure and prevention.

But there were just a couple of folks (albeit arguably more qualified than the previous ones, which are more "hands-on" kind of guys) who suggested that epoxy treatments are way overrated, and their popularity among refitting yards is mostly due to the fact that they are easy and fast to make.
According to them, epoxy resins make sense only when the hull is already badly affected by osmosis, while they are not so good for prevention alone.
Reason being that epoxy does not chemically bond with the hull surface, but just micro-attaches mechanically to any surface irregularities.
In turn, this means that the adhesion on a very smooth surface is poor, and prone to detach over time.
Now, of course gelcoat, when a bit old and after being sandblasted, becomes a bit porous and surely offers a better grip, compared to a brand new and shiny boat.
But the reasoning still stands, in principle.
So, in their opinion, for a hull which is essentially sound, it's better to use a vinylester resin, which grants a better/stronger chemical bonding, for minor re-touching wherever necessary.
After that, they recommend a new coat of gelcoat on the whole bottom.

Costwise, the differences are neither here nor there, in the grand scheme.
But the two routes are obviously very different, and needless to say I'd rather choose the best/more longlasting one.

As a side consideration, I'm also wondering if going for epoxy alone vs. vinylester+gelcoat can somehow affect/restrict the choice of going for Coppercoat vs. traditional a/f afterwards.
On this specific point, nobody gave me a firm/reasoned suggestion, though this probably has to see with the fact that CC is not popular at all, around here.
Actually, one thing I remember from a previous debate is that since CC uses a water based resin, it's not compatible with solvented epoxies.
But I guess that this is just a matter of using an appropriate product if going for epoxy, while I don't think there's any restriction to applying CC over gelcoat.
Happy to stand corrected from those in the know, though - TIA for your comments!

 

[BruceK]

Isn't gelcoat a polyester resin hence the requirement of vinylester resin and if so where does your concern 're epoxy solvents fit in?

More to the point why not CC directly to the hull now?

(Apologies for answering a question with questions)

 

[Tranona]

Don't think it is just fashion - that is just to me a throwaway line for something you don't agree with - for whatever reason.

The point is that gel coat is more permeable than epoxy so it makes sense when you have the hull clean to apply a less permeable coating before applying antifoul. The process has been around long enough for it to be well proven. Remember that UK boats have more experience if that's the right word of osmosis and the failings of gelcoat (and the underlying laminate) partly because of the age of boats and partly because of the materials and processes used when they were built. As a result epoxy coating of underwater parts of the hull is common in the UK on both older boats after blasting and on new boats.

 

[BruceK]

Yes but wouldn't CC fulfil the same function in this instance?

 

[KevB]

Yes but wouldn't CC fulfil the same function in this instance?

That'a my thought too. I had the hull sodablasted about 11 years ago and coppercoated onto the bare hull. Been working perfectly since.

 

[MapisM]

Don't think it is just fashion - that is just to me a throwaway line for something you don't agree with - for whatever reason.

I couldn't be more far from not rooting with either theory. If by using the term "fashion" I gave this impression, it was not intentional.
Personally, based on what I heard so far, I can see pros and cons in both alternatives, but I'm actually in doubt - hence this thread!

Btw, nobody argued against what you are reporting as UK-specific experiences with full blown osmosis ("failing of gelcoat and the underlying laminate").
Afaik, a complete gelcoat stripping followed by a proper hull drying and eventually epoxy treatment is the undisputed recipe, for these cases.
The focus here is on whether it's appropriate to epoxy coat a 14 yo hull which shows no signs of osmosis (and was originally laminated with vinylester resin, FWIW), or it's sufficient to stick to gelcoat.
According to a couple of professionals with a long experience in hull moulding (btw, neither of them were aiming at getting any job, because they knew beforehand that whatever I will do needs to be done too far from where they are based), this second alternative is not just sufficient, but even better...

 

[MapisM]

More to the point why not CC directly to the hull now?

Well, that's a possibility, I suppose.
Those two folks who suggested to use a vinylester filler for the few re-touching where appropriate, and then finish the whole hull with a fresh gelcoat layer, did not say that with CC in mind.
It was rather a general suggestion on how to bring back the whole hull to essentially as-new conditions, exploiting the opportunity given by the fact that all the a/f is completely removed.
In their view, that leaves open any possibility afterwards, be it CC or traditional a/f.
But maybe you are right - would CC be the final choice, maybe it's pointless to restore a perfect gelcoat surface underneath, before going that route...?

 

[rafiki_]

P, Rafiki has also been stripped back from old A/F, and any blisters are being filled. Note also dry hull and no osmosis, despite her being an Azi :encouragement:

We are going to apply a resistant finish prior to CC. Can't recall what is it, but will check and get back to you.

 

[BruceK]

My understanding is it's not a good idea to have the gel coat too thick nor should gel coat be applied over gel coat, but rather direct to the grp so I am at a bit of a loss as to why the pro's said that, but bow to their knowledge.

They are correct in saying use vinylester filler if you plan to re gelcoat as epoxy and polyester dont bond well.

If you plan to CC I believe that would serve the same function as a protective epoxy coating and have the same longevity.

I would not bother to re gelcoat only to put CC on top. Any as new benefits will be shortlived between coatings and then you'd be back to square one once the CC needs to come off for replacement.

As for re-gelcoating before applying AF, as the problem is very minor at the moment, it seems an extraordinary amount of effort and no small risk for very little gain and if it were mine I'd have a pro check the thickness and porosity of the gelcoat if you have aggressively cleaned off the gelcoat with soda / sand blasting. I know when I investigated doing mine last year the local grp expert did recommend that it would be a good idea to have this checked and remedied if necessary. He was not a fan of this technique of cleaning off old AF despite it being an additional revenue stream for him post blasting.

 

[Portofino]

You said in post #1

“Sandblasted first, then finished by hand with fine orbit sander -“

That’s code to me translated to - - irreversible damage to the underlying protective surface increasing any existing porosity to such an extent microscopically that a new barrier layer ought to be replaced in an attempt to get it back as it was .

So in my book something needs reapplying ( everywhere not just the little odd patch repairs that you acknowledge need doing )

I would try and put back what has come off .When you think it’s ready ——

Then use normal AF

We know that works and it’s the route of least complications .

It’s not a “fashion “ adding a layer of somthing after a hull something” blast “— it’s a repair job plane and simple !

 

[Portofino]

This phase from post #1 - needs a bit of a mauling too if folks don,t mind ?

“Reason being that epoxy does not chemically bond with the hull surface, but just micro-attaches mechanically to any surface irregularities.”MapishM

Most inert substances from a chemical,molecular level don,t “ chemically bond “ otherwise they would react with anything that came into contact and they don,t .

Stuff adheres - I like that word adheres better than “ chemically bond “ and think that’s a better description how any new covering will attach to your hull .
Sure a greater if not completely aspect of the adherence is micro mech bonds - don,t get hung up over that that’s the science .
They all micro - mech bond all adhesives .

Remember after it’s “ blast “ then scape with a sander it’s as ready for a micro mech bond more than it’s ever been now .

The smoothest and least pours surface was created when the gel coat set in the mould 14 years ago .That set actually was a true chemical set through n through It can,t be repeated now as one batch .

Any further additions will be micro - mech bonds anyhow even the same stuff .

So Tarona,s post #3 is sound advice :encouragement:

 

[jfm]

I think it's fashion more than science. You have good laminate with vinylester, so just apply gel coat. People talk about permeability but does it really matter if a few water molecules get through? Selling these epoxy coatings seems to use a business model with a few things in common with the RC Church: instill a fear of what will happen if you don't. So I'm gelcoat all the way. But you will also be ok if you use epoxy and you'll be fashionable :encouragement:. Or just use good quality paint

 

[MapisM]

P, Rafiki has also been stripped back from old A/F, and any blisters are being filled. Note also dry hull and no osmosis, despite her being an Azi :encouragement:

We are going to apply a resistant finish prior to CC. Can't recall what is it, but will check and get back to you.

Thanks P, that would be interesting to hear.
If I may ask, how old is Rafiki, and how did blisters look like on her hull?
Just for comparison, this is one of the "bubbles" found along the rails of mine.
The gelcoat around it looks very rough mostly because of the pic enlargement: the bubble diameter is about 5 or 6mm.
Of course, on top of the age, the sanding contributed to make it a bit porous (no way to avoid that, afaik), but it's actually in very good conditions overall.
Besides, the GRP visible under the open bubbles is very solid, smooth and bone dry, with no signs of "craters" and fluid release anywhere.
Still worth filling/smoothing while the hull is "naked" of course, but none of the folks who saw the real thing told me that there's any reason to be concerned.
Even those who suggested the epoxy preventive treatment, only said so along the lines of "why not take the opportunity", more than for a real need...

 

[MapisM]

As for re-gelcoating before applying AF, as the problem is very minor at the moment, it seems an extraordinary amount of effort and no small risk for very little gain and if it were mine I'd have a pro check the thickness and porosity of the gelcoat if you have aggressively cleaned off the gelcoat with soda / sand blasting. I know when I investigated doing mine last year the local grp expert did recommend that it would be a good idea to have this checked and remedied if necessary. He was not a fan of this technique of cleaning off old AF despite it being an additional revenue stream for him post blasting.

I see his point, but is there any equally effective method for stripping old a/f, that doesn't affect the gelcoat surface at all?
Down here, nobody recommend alternatives. If anything, it's just a matter of choosing someone with the proper expertise doing the job, which I obviously did.
Ref. re-gelcoating, I agree that it might be unnecessary, and even more so if going for CC.
But according to those folks who suggested to go for it, a thin gelcoat layer would be neither a difficult nor a very expensive job, at this stage - comparable to epoxying, anyway.
By checking the gelcoat thickness and porosity, do you mean visually, from someone with the proper experience (which I already had, with reassuring results), or are you aware of a somewhat scientific way to measure that?

 

[MapisM]

The smoothest and least pours surface was created when the gel coat set in the mould 14 years ago.

Well, of course the gelcoat on the hull of my Fountain, which had never been left in the water and never antifouled, was more shiny.
But that's hardly an option, with a larger boat meant to spend most of her life at sea.
In a sense, any gelcoat surface begins to be damaged while preparing the hull for being antifouled the first time.
If you are aware of a way to avoid that, in your boots I'd rather have it patented before disclosing it in a boating forum...!

 

[MapisM]

I think it's fashion more than science. You have good laminate with vinylester, so just apply gel coat. People talk about permeability but does it really matter if a few water molecules get through? Selling these epoxy coatings seems to use a business model with a few things in common with the RC Church: instill a fear of what will happen if you don't. So I'm gelcoat all the way. But you will also be ok if you use epoxy and you'll be fashionable :encouragement:. Or just use good quality paint

J, you summarized EXACTLY my sentiment after hearing a bunch of contrasting views - which in fact is what inspired this thread! :encouragement:

 

[Portofino]

I,am looking at the area around the burst bubble .
It never came out of the mold that rough - see what I mean about damage repair ^^^

Time consuming as it is I would be inclined to stear away from a quick blast to remove AF .
There’s are AF removing gels available - I’ve seen then all used in the yards - messy sure ,extra time consuming sure *but no rough surface ends up back to as was when it’s was popped out of the mold .

* whole family’s working small area,s takes about a week for 3/4 pax to do a 50 ftr

 

[rafiki_]

Thanks P, that would be interesting to hear.
If I may ask, how old is Rafiki, and how did blisters look like on her hull?
Just for comparison, this is one of the "bubbles" found along the rails of mine.
The gelcoat around it looks very rough mostly because of the pic enlargement: the bubble diameter is about 5 or 6mm.
Of course, on top of the age, the sanding contributed to make it a bit porous (no way to avoid that, afaik), but it's actually in very good conditions overall.
Besides, the GRP visible under the open bubbles is very solid, smooth and bone dry, with no signs of "craters" and fluid release anywhere.
Still worth filling/smoothing while the hull is "naked" of course, but none of the folks who saw the real thing told me that there's any reason to be concerned.
Even those who suggested the epoxy preventive treatment, only said so along the lines of "why not take the opportunity", more than for a real need...

Rafiki built 2002. Blister looks just like your pic. Will be filled. As with yours, mine on the spray rail. Agreed, no Osmosis, hull moisture readings good, so fill, cover and CC.

 

[MapisM]

Rafiki built 2002. Blister looks just like your pic. Will be filled. As with yours, mine on the spray rail. Agreed, no Osmosis, hull moisture readings good, so fill, cover and CC.

Yup, I suppose that's not just the simpler, but also the most effective way to go.
Still interested to hear what product you will use as "resistant finish prior to CC", if you'll have a chance to check.

 

[MapisM]

There’s are AF removing gels available
...
takes about a week for 3/4 pax to do a 50 ftr

Well, that has to produce better results for good, in order to compete with 1 day/2 pax...
BUT, is it worth? I understand that my pic seems to support your view on sandblasting damaging the surface, but trust me, if you carefully swipe your finger between the sandblasted hull below the w/line and the shiny hull sides, you struggle to feel the difference.
The "irreversible damage", as you called it, is extremely superficial - and probably makes for a better grip of any kind of a/f you wish to use afterwards, btw.
My bet is that if I would sandblast again the hull in another 15 years or so, the gelcoat would still be good enough to not NEED another coat.
Whether I WISH/LIKE to put another coat of gelcoat for peace of mind, that's another matter altogether...