Fiberglass work prep

[bobge...@gmail.com]

Hi -

I need to do some fiberglass work on the inside of the hull on my Nonsuch. To prep for the new glass, I’m assuming I’ll need to remove the paint first. Any suggestions for doing that? I was thinking of using the Citristrip product. 

Thanks -

Bob Gehrman

NS36 #52 “Fortunate”

East Greenwich, RI

[Ward Woodruff]

Hi Bob,

You might consider 40 grit disc on a random orbit sander hooked up to a shop vac. The setup should keep the mess down and you will end up with a coarse sanded surface to which the new resin and glass will bond. 

Ward Woodruff

N33 #8 Margery

Niantic Bay, CT

On Dec 11, 2023, at 8:58 AM, bobge...@gmail.com <bobge...@gmail.com> wrote:

Hi -

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[JohnS]

Bob;

I used an oscillating tool with a tool with a "diamond" tool for working on ceramics; it removed the roving highs, getting down to the paint in the lows easily. The mess stayed nearby, and vacuumed up easily. 

You know about vinylester and epoxy differences, I presume? Ignore comment if you do. 

JohnS NS26C 046 covered for the winter in Bath, ON.

[Bob Gehrman]

Thanks John - Is there a preference or requirement of glass basis on the hull? Epoxy vs Vinylester?

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[JohnS]

Bob - My understanding is that Gelcote is vinyl-based, so the resin used in the hull layup is vinyl-based, too. It makes for a chemical bond, not a mechanical "friction" bond, with the Gelcote.

Also my understanding is that you can epoxy over vinyl, but you can't vinyl over epoxy and get a chemical bond. Again (disclaimer) epoxy is stronger; vinyl fibreglass roving has a layer of matt so that the vinyl resin has more fibre and less plain resin between layers. You don't have to use the roving/matt combo if using Epoxy.

I'm no expert in this, so read or listen for other opinions. 100% of my fibreglass work has been done under supervision of professionals, first one summer circa 1980 under Scotty Murray who ran the boat repair in Niagara-on-the-Lake sailing club (and previously worked as a wooden boat builder for Chriscraft??) and laterly with the help and guidance of the workers at my local marina's boat repair facility.

I can also say with certainty that, should one drip drops of epoxy resin on the repair facility's concrete floor, one can quickly grind it off after it has hardened with said oscillating tool with diamond blade in seconds, and the resin "disappears" and nobody's the wiser. (sheepish smile).

So, to sum up, vinyl over vinyl, epoxy over vinyl, but NOT vinyl over epoxy.

Anyone with corrections/additions, *please* feel free to comment -I'm certainly no expert here, so we'll all learn and be better for it.

JohnS NS26C 046 Bath ON 

[Bob Gehrman]

Thanks John - That's been my understanding too. 

However, is the interior of the hull covered in Gelcoat? I thought the gelcoat was placed into the mold, and then everything else was just fiberglass. I assumed the interior hull finish, where exposed, is just painted.

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[JohnS]

Gelcoat (Gelcote??) is just a paint. I've got some white here for eventual touching up the interior flat surfaces where dings and drilled holes were. From what I remember going through C&C shops, it's just sprayed on the female mould then fiberglassed over. 

To answer your specific question - I *assume* the grey colour is gelcoat. The reason for this is that a) it looks like oxidized gelcoat, and b) the factories likely got it in large quantities, and had experience in using, spraying, cleaning it. 

Whether or not it is or is not actually gelcoat grey inside our boats, I have no idea. All I know is that the experts say to grind back to pure glass, removing the 40 year old outer "stuff" (paint, oil, dirt...), so that is what I did!

BTW, when re-painting the grey insides, I use bilgecoat grey or white; I know others here use other oil-based paints; which are likely twice as good and half the price as the boat-specific stuff!

I'm no expert here, just did what I was told and asked lots of pointed questions to the experts - again - corrections more than welcome. 

JohnS NS26C 046 Bath ON.

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[Bob Neches (Me Gusta, Nonsuch 26U #233)]

I don't believe the interior grey is gelcoat, I believe that it's more conventional paint -- whether oil- or water- based probably depending on the history of the specific boat.

I'm not an expert, and don't know the terminology, but I don't think gelcoat and paint are the quite the same thing.  My impression is that gelcoat is the same resin used in the fiberglass, with pigment added but without the glass fiber reinforcement.     I always thought the the appropriate analogy is concrete cement.   Fiberglass is like steel-reinforced concrete, gelcoat is like added pigmented cement to the outside of a steel-reinforced concrete structure.

I also think that part of the difference has to do with when in the process it's applied.  Gelcoat and fiberglass get combined when both are wet, and harden together.  Paint is applied to an already-hard surface.  (Except in the case of wet fresco painting, which gets us into art, which takes us even further away from things I really know anything about.)  This leads to differences in the chemistry affecting how well the layers bond together.

However, regardless of whether I'm even correct, I doubt that these distinctions really affect the original questions Bob raised.   If you're adding fiberglass to the interior side of , you need to sand down to the laminate to bind the fiber-reinforced glass layers being added to the fiber-reinforced glass layers already there.  If there's currently paint there, you wouldn't want to try to bond to it because it has no strength.  If there's currently gelcoat there, you wouldn't want to bond to it because there's little strength there.

You want to use epoxy, I'd think, for no other reason than that seems to be the current standard.

The purpose of gelcoat on the exterior is partly cosmetic, partly because it provides a smooth surface (which matters for friction-reduction below the waterline and ease of cleaning above), and partly for UV-protection.   The only thing that really matters in the boat interior other than in living areas is ease of cleaning.  So, paint is the way to go.  My impression is that the newer water-based bilge paints are competitive in quality with the older oil-based, and both cheaper to buy and easier to clean up.

FWIW, IMHO.

-- Bob

   Me Gusta

   Nonsuch e26U #233

[Brian M. Godfrey]

   Yes, gelcoat in boats of our age is polyester resin with pigments and thickeners to keep it from running down the vertical surfaces of the mold before it is cured.  It is purely cosmetic and is quite brittle (hence stress cracking) so thinner is actually better.  It is sprayed onto the inside of a female mold and then the fiberglass layup is built up over it with the final layer being the one you see on the inside of the hull.  While it is certainly possible to sand that inner surface down and spray on a gelcoat, that's not how my boat was finished and I doubt that any Nonsuches were.  Mine is either painted where it will be exposed (like in the lazerette) or left unfinished where it will not usually be seen or come into contact with human skin.
   There are many layup schedules for making molded fiberglass parts.  Given the age of our boats, I suspect that the fiberglass layers were probably wetted out with polyester resin and laid into the mold one by one, then the cores (if any), then more layers of wetted out fiberglass, then the whole thing was probably vacuum bagged to press it all into shape and hopefully suck out some extra resin.  I know that some more modern fiberglass layup schedules actually involve laying up all of the dry parts, applying a vacuum, then sucking in the resin and then heat curing in giant ovens.  Somehow I don't think our boats were likely done that way, but maybe some old timers actually know.

   You'll notice that these layup schedules rely on the gelcoat being already cured before you start the layup.  So you've got fresh polyester resin stuck onto cured polyester gelcoat.  And if you look at impact damage you will see that the gelcoat separates from the underlying fiberglass layup pretty easily.  That's because there is only a mechanical bond, not a chemical bond like you get between the fiberglass layers.  This is just an example of the polyester to polyester bonding problem.  Epoxy creates a much stronger mechanical bond than polyester which is why it is the standard for repairing polyester laminates.  Vinylester is in-between the two, but why half-ass a repair with that when you can use epoxy?

--Brian M. Godfrey
  br...@wildbirdshop.com

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