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Flaking Gel Coat

Glenn A

New Member
Hi! New participant and Sunfish owner. I have a 70's Sunfish that I've been working on. It's sailable now but the gel coat around mast is cracking. I'm thinking that I might like to pretty it up over the winter by getting rid of stuff that's flaking, filling in cracks and painting but would like some advice on how to do it. Thanks!!20220721_104837.jpg20220721_104751.jpg
 

L&VW

Well-Known Member
It's earlier than a '71, so it's seen some use. :oops:

I'd press firmly in the damaged area to listen for structural integrity, but in any case, sand down to where you can see undamaged fiberglass. (I suspect this is an area of prior "intervention", but could always be wrong :cool:).

Note: It won't be easy. Sunfishes' outer surfaces tend to crumble as they thin. Repair is still possible, but could be daunting.

If the deck doesn't protest your forceful push, you could sand the area smooth, then level it with a layer of Marine-Tex. Still more sanding should bring it back to new. Skill in sanding is important, as paint is unlikely to cover errors.

Marine-Tex is a very hard epoxy, so be patient with the process. ;)
 

Glenn A

New Member
It's earlier than a '71, so it's seen some use. :oops:

I'd press firmly in the damaged area to listen for structural integrity, but in any case, sand down to where you can see undamaged fiberglass. (I suspect this is an area of prior "intervention", but could always be wrong :cool:).

Note: It won't be easy. Sunfishes' outer surfaces tend to crumble as they thin. Repair is still possible, but could be daunting.

If the deck doesn't protest your forceful push, you could sand the area smooth, then level it with a layer of Marine-Tex. Still more sanding should bring it back to new. Skill in sanding is important, as paint is unlikely to cover errors.

Marine-Tex is a very hard epoxy, so be patient with the process. ;)
Just guessing at the age. Can't find a serial number on it. Had old style bailer that I've removed and replaced with newer style, there's no storage area in cockpit and it's heavy as hell even after drying out completely.
 

signal charlie

Well-Known Member
Staff member
As mentioned above, remove the old surface coating by sanding and see what's underneath. It might have been painted. I suspected that was a repair area but they did a good job of blending if that is gelcoat. Depending on what you find might send you down the path of gelcoat or paint, and depending on which of those paths you choose you need to choose the correct repair materials that will be compatible with either gelcoat or the type of paint you choose. Example, we've heard tales that gelcoat is not compatible with an epoxy based repair, but I've been told that it will work if you use the correct primer over the epoxy.

Post a few more pictures of the entire deck, that might help the determine the manufacture date. Or if it has a Serial No. tag by the coaming post a pic of that. Either way it's 1960-1971.
 

Roller

Active Member
The crackle on the deck looks like failed paint.

For several reasons vinylester resin is superior to epoxy for the repair of older polyester laminates, especially if new gelcoat might be involved. Vinylesters are a sort of way-station between straight polyester and more capable epoxys. Vinylesters typically have chemical resistance, impact, and mechanical properties close to epoxy (and superior to polyester), but are similar enough to polyester to be reliably compatible with things like polyester gelcoats.
 

mixmkr

Well-Known Member
Gelcoat is typically fine over epoxies. Most epoxies will " blush"...similar to the wax rising in waxed gelcoat or finish resin. It then needs to be removed with washing and THEN sanding to create something to "grip" for the gelcoat, creating a mechanical bond. Sanding first will just force the wax like blush, into the grooves giving a usable appearance...ah...but dont be fooled. Unlike a mechanical bond, a chemical bond is when using like materials, successive layers 'meld' somewhat into each other and create the most superior bond to each other.
 

signal charlie

Well-Known Member
Staff member
As per gelcoat over epoxy, what mixmkr said. I talked to a Tech Team rep at Jamestown Distributors yesterday and their tips were to make sure any epoxy has fully dried, give it a few extra days. A quality 2 part primer is the way to go, let it dry. And don't oversand into epoxy based components, like fairing compound, below the primer. Follow the application instructions for whatever system you choose.

If you get into polyester resins there are choices between those with wax and those without. At one point wax has to be used on the last coat or a PVA to get the poly to harden, and then once it is hard, dewax to get a good surface for gelcoat.

We've been told that there is a lot of precise measuring for polyester, and strong odors from the catalyst? That's enough to keep us from trying it, plus most of our restorations are so severe that the boat is going to get painted. Be sure to select proper PPE, such as a P100 respirator.

As we learn more about gelcoat, we may try a few gelcoat patches here and there....over epoxy. Our friend Howie used to do mast step repairs and he said he'd brush on gelcoat in the shape of a Sunfish logo sometimes, vs trying to color match.

Whatever route is chosen, it will be fun.
 

mixmkr

Well-Known Member
Btw, ive stopped using waxed gelcoat years ago. Spraying or applying PVA (wax) over a finish application to seal off the oxygen contact, much more plastic wrap...just ruins the finish surface most of the time. I like to use a sprayer for gelcost, most of the time a disposable Preval sprayer.
But a "secret" ingredient is Duratec (I'll let you google that) added in proper amounts, smooths out a sprayed gelcoat and adds a shine, like you wouldnt believe...probably the best benefit...but it also eliminates the need for using wax. The finish spray ends up that with proper prep, I can come back with a light sand of #400 or higher sandpaper ...and just sand the feathered edges to minimize a repair "halo" around the repaired edges.....then a final powet buff. Duratec truely is amazing stuff and makes adding wax, akin to prehistoric times!
 
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mixmkr

Well-Known Member
lastly...on repairs i dont care about so much...i dont even sand... as the finish spray is "that" good....and the feathered, sprayed edges blend the color best. But "critical' repairs require superior color matching and sanding, smoothing the sprayed edges to get a consistent sheen as well. Sunfish bottom repairs...I wouldnt sand...a $200,000 black Colbalt with a mirror finish...yes if I want repeat work!
 

Roller

Active Member
Mixmkr's comments and recommendations here are excellent.

Applying polyester gelcoat over an epoxy laminate or epoxy patch *can* work, but doing this means combining materials of quite different chemical and physical properties. For any hope of success the epoxy substrate must be *fully* cured (common epoxies can take days or weeks--or even longer--to completely cure), and as mixmkr notes, the epoxy substrate must be scrupulously clean, completely dust free, and abraded so as to provide substantial tooth for the gelcoat.

Also, be aware that although the styrene stench from polyester is much more objectionable than the odor from most epoxies, epoxies are the more potentially harmful resins, *much more* likely to cause long term chemical sensitivities than polyesters. If working with polyester OR epoxy you *always* need to wear complete PPE: an organic respirator, nitrile gloves, eye protection, barrier cream for uncovered skin, etc. Never let resin touch unprotected skin, and *never* use a solvent (even vinegar) to wash resin from skin (the solvent increases skin absorption of harmful chemicals).

Remember that laminating resins remain chemically active even after they go solid and feel cured (epoxies are chemically active much longer than polyesters). If you sand, file, or saw newly cured fiberglass laminates or resin patches you must *never* inhale the fine dust you create--it can be quite harmful. Be careful also to keep the dust out of living areas and to wear disposable clothing. See this West System advisory: Preventing Overexposure
 

mixmkr

Well-Known Member
The above precautions are definitely relevant. The huge bulk of my work is in open air and strategically placed fans help. That said, fresh fiberglass is like that "new car" smell to me.
;-)
Btw.....im down to one fish nowadays...as my boat repair biz really eats up free time. I havent posted much here lately, but I'm an excellent lurker.
Heres my 69 pride and joy. Ive had many boats ...but I think ive had the best time on a Sunfish...even though I have to sail it alone
 

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