Gel coat over epoxy resin question

[Guest]

Um, asking for a friend and all that. I am a gel coat virgin, saving myself for the right boat.

We have again repaired the worn down through the gel coat and into the kevlar cloth stems on a couple of boats that see hard limestone, oyster bar, wormrock and beach landing and sandy drag ashore use in the Everglades.

Last fall we experimentally tried using S glass, E glass and Dynel in different wear areas, installed with a mixture of G/flex and West 105, peel ply on top on a couple boats.

The installation was well accomplished. However, neither or E glass lasted a season, while the Dynel is still going unscratched strong.

Back at it again. All Dynel this time. We sanded and cleaned those previously repaired boat stems, and laid the same resin mix atop long, thin, precisely cut strips of Dynel on the stems. Both boats looks great so far, the Dynel flush and compressed under the peel ply without bulging epoxy soaked like an old sweatshirt. Sweet.

I beveled the tip ends of the cloth after it cured, and needed to use a file to make any progress. Dynel is tough freaking stuff. Stem tips file beveled smooth and re epoxied. It looks niceeeee. So far so good.

What also wore off, starting on the first trip, was the enamel spray paint we applied over the resin last fall for UV protection. Those boats are worked constantly in a harsh environment for 5 months, and then spend much of the rest of the year outside on a trailer. Some UV topcoat is called for.

We, shop partner Joel and I, have been back and forth about what to use as a more durable than spray paint UV protectant top coat.

One part and two part poly and epoxy boat paints are pricey, and in Everglades conditions I doubt even their longevity as a UV top coat. Nix that idea until at least next fall when the boats come back for their annual tune up. I never shoulda mentioned that lifetime warranty nonsense, and probably should do that warranty work in the spring after hardest use.

Our shop debate regards top coating those now lovely deep vee Dynel stem protectors.

I want to simply brush on, not micron thin spray on, a coat or two of ubiquitously available Rustoleum enamel paint, which I already have in the shop in the needed colors. And do that every year in paint worn areas. Four bucks a can.

My shop partner, whose boats they are, bought a can of ClearCote white with wax gel coat and has unperturbed visions of rolling gel coat atop the epoxy and Dynel as a thicker sacrificial layer. And I have done my best to perturb him.

Trying mightily as I can to conceal my bias, I am horrified at this idea, and will not list all of my concerns, but believe it will look like stucco without days of sanding and recoating. That it will, at best, spider crack or chunk off at any impact. That it will be a massive PITA to sand back down to epoxied fabric is it fails.

That it may not adhere well to cured and amine blush removed epoxy resin (researched opinions vary)

None the less, I kinda want to see him try it. I did have him sign a notarized agreement to hold me gel coat blameless, so whadda I have to lose?

What say yee who have worked with gel coat?

 

[stripperguy]

By gel coat, I take it you mean polyester resin.
Assuming it is polyester (or maybe vinylester), you should put this in the back pocket of your bad idea jeans.
Polyester over epoxy is generally not recommended. Epoxy over polyester is OK...

As an alternate solution, how about some RAKA UV inhibited epoxy resin to wet out the Dynel? No more concern about UV degradation, great adhesion, you could even mix in some pigment.

 

[Guest]

By gel coat, I take it you mean polyester resin.
Assuming it is polyester (or maybe vinylester), you should put this in the back pocket of your bad idea jeans.
Polyester over epoxy is generally not recommended. Epoxy over polyester is OK...

As an alternate solution, how about some RAKA UV inhibited epoxy resin to wet out the Dynel? No more concern about UV degradation, great adhesion, you could even mix in some pigment.

Yes, I believe what he bought is polyester gel coat, ClearCote with wax white gel coat.

I had often heard that gel coat over epoxy resin is a bad idea, but research shows differing opinions. If any amine blush is removed it may be ok, at least in the sense of curing properly.

The Dynel rub strips are already installed, using a mix of G/flex and West 105/206 slow hardener. If I had had some epoxy resin with UV inhibitors in the shop I would have used that.

 

[stripperguy]

Yes, I believe what he bought is polyester gel coat, ClearCote with wax white gel coat.

I had often heard that gel coat over epoxy resin is a bad idea, but research shows differing opinions. If any amine blush is removed it may be ok, at least in the sense of curing properly.

The Dynel rub strips are already installed, using a mix of G/flex and West 105/206 slow hardener. If I had had some epoxy resin with UV inhibitors in the shop I would have used that.

I've read about it as well, also finding some data indicating it may be OK.
I happen to be an aggressive sort of guy, in most aspects...but when it comes to materials, I stick with proven results. Too many years in research, I suppose.
A thin overcoat of UV inhibited epoxy resin is still a possibility, right?

 

[Jim Dodd]

Mike
I've used RAKA's UV inhibited epoxy resin, in fast and slow hardeners. It hasn't had enough Sun exposure, to really test it.

I'm with Stripper guy on this. Conventional wisdom says No.

If you did use gel coat, the worse it would do is delaminate, and you would just need to do it again. Nothing ventured, nothing gained! Give use a full report if you go the gel coat route!

Good Luck !

Jim

 

[pblanc]

I have read accounts of polyester materials applied over cured epoxy working. And I have read horror stories of polyester resins failing to cure when applied over epoxy, even when the epoxy was thoroughly cured and well-washed. When it has failed, it sounds as if it created a grand mess. Personally, I wouldn't try it. If you do, I would to a test application on a small area.

 

[Guest]

My biggest concern, not mentioned above, is that not only might the gel coat spider crack, or even chunk off pieces on any hard impact, but if it proves unsatisfactory it will be a massive PITA to remove completely before applying a different UV top coat. Especially if we leave the faint peel ply weave for better mechanical bond. We would have to sand down into the Dynel fabric to get it all out. Good luck with that.

Gel coated boats, from what I have read, are laid up in the mold with the gel coat spayed on first and the cloth and resin applied soon after, presumably for some chemical bond. Not only would this be poly gel coat over epoxy resin, but the resin has fully cured.

At least there is no amine blush. We used 206 slow hardener, with peel ply so any amine blush should have been atop the peel ply. The boats have been washed with a virgin ScotchBrite pad, rinsed with clean water and washed again with alcohol. And we will clean them again immediately before any top coat. If it fails it will not be because of amine blush.

I have read that gel coat does not store very well over time, even over a short period of time, so this twenty dollar pint can of gel coat may be unusable by the time next years annual repairs roll around. He who owns the boats would not want to waste the leftovers in the will not keep for a year can of gel coat, and seems intent on doing both long narrow (60 by 1 and a half inch) Dynel rub strips.

I am hoping if I have him read the advice and opinions given here he will be dissuaded, at least from creating 120 inches of mess to be laboriously sanded off next year. At best I may be able to persuade him to do only a small gel coat test area on one stem. I would feel better about laughing next year as he mumbles razzenfrazzenfrickin as the gel coat sanding dust flies.

I do love an experiment, and that could be three experiments in one. How well will the gel coat over epoxy resin fair in abusive limestone and oyster bar conditions? Will the opened can of gel coat still be usable a year later? How much of a PITA will it be to remove the gel coat layer if it proves unsatisfactory? My guesses

Not well
Not at all
Not just a minor PITA

 

[BWCA66]

Gel coat does have a limited life, they usually garantee 90 days. Not sure how long it lasts but I have had it go bad in less than a year, may depend on color and pigment. Gel coat needs to be fully sealed off from air to fully cure. You can buy an additive to make it cure and greatly reduced the orange peel effect but then you double your cost. That said I think it would adhear to roughed up epoxy.

 

[Guest]

Gel coat needs to be fully sealed off from air to fully cure. You can buy an additive to make it cure and greatly reduced the orange peel effect but then you double your cost.

The gel coat is the with wax already added variety, from what we have read that sets up without a cover or additional additive. Hopefully that will also eliminate any orange peel finish, but whadda I know?

My other gel coat over Dynel and epoxy concerns remain.

At the least I foresee us doing at least a small test area with gel coat. Somewhere easy to sand off next year if the results are unsatisfactory. At best (worst) we'll know next year

 

[Alan Gage]

I'd highly recommend not trying it. I've been there and done that.

Maybe this link can help convince Joel: http://www.canoetripping.net/forums/forum/general-paddling-discussions/diy/52804-barrens-build/page7

Tell Joel to put some masking tape on the exposed stems when the boats go on the rack for an extended period of time and then repaint them when they get back in the shop.

Alan

 

[Guest]

Saying no to gel coat

Thank you all. Joel is now convinced that gel coat over epoxy resin as a UV barrier is a bad idea. If I had known that a week ago the boats would be done by now. And I could have knocked over a pot of white enamel paint on the workbench.

In a continuing effort to perplex Joel I am now taking the gel coat side, at least experimentally.

The white bottomed boat now has a Dynel and resin mix patch over a small crack in the center, right under the seat. In the flattest surface area of the hull, where it would be easiest to sand off next year. Now I really want to try the gel coat experiment, if only for nope validation.

I like Alans idea of just running some masking tape over the paint worn areas in the spring, but I think our annual timing is backwards on this one. The boats are used hard all winter and sit largely unused and UV exposed for most of the summer. We should be refreshing the scraped off paint in the Spring, not the Fall.

The shop is a mite crowded with three 17 foot boats stuffed in. It is tough to walk around. Yesterday I walked full speed into the sharp bow tip of one boat on sawhorses. Two inches to the left and I would be typing soprano.

It will not get less crowded any time soon. As soon as these three go back on the trailer a 20 foot Miramichi come in for some outfitting, including, thanks to a cunning metal worker friend, a very cool custom design and custom built motor mount.

All quarter inch welded aluminum plate. Height adjustable for different shaft length motors.

Note to anyone considering a double ended motor canoe. A short shaft motor will not be low enough with a standard horizontal motor mount to position the prop below the bottom of the hull, especially on a deep canoe. The boat will not turn willingly to the left with the prop wash hitting the side of the hull.

 

[Guest]

Gel coat over epoxy resin 24 hour cure results

Yesterday we top coated the newly installed Dynel cloth and epoxy resin mix. The epoxy had peel ply laid overtop when applied, and with the peel ply removed the resin dried for almost a week until sandably cured.

I guarantee there was no amine blush remaining. We used a blush removing peel ply layer, and once cured the resin was scrubbed with soapy water and a new ScotchBrite pad, clean water rinsed and alcohol wiped. We even cleaned, rinsed and dried the resin area a second time a few hours before top coating.

The long narrow Dynel run strips on the stems were UV top coated using Rustoluem white enamel paint and were dry to the touch in 5 or 6 hours and fully dry the next morning. Any amine blush would have screwed that up. Been there.

The experimental gel coat brushed thinly atop the small center patch was still tacky in linear streaky smears this morning, despite keeping the shop at 72F for a full day.

FWIW, the gel coat was the type with wax already added, which from the literature does not need a barrier layer or additional wax additive. Or so we thought.

The gel coat was well mixed in proper catalyst proportion.

The shop is still at 72F and I have the boat back right side up with a radiant oil heater directly under the still tacky gel coat. I do not have high hopes, but if it never cures it will soon be removed by oyster bars and limestone.

I have no clue what went wrong. I know what we did right.
Fresh, unopened can of gel coat bought a couple weeks ago
Carefully measured and properly mixed.
New, clean unused mixing cup and fresh clean brush. We only made 2 ounces of gel coat in a graduated cup.
Not amine blush
Not uncured epoxy. The repairs made epoxy resin dust when sanded
No too cold. Min max shop thermometer shows a brief low of 68 when we had to open big shop door to bring a 20 footer inside, otherwise a steady 72 F for a full day and counting.
Not too humid, the highest shop hygrometer got was 57 percent.

Uneducated guesses
Maybe using the gel coat type that requires a barrier layer or additional wax additive would have been preferable.
Maybe this can of gel coat sat on the vendors shelf for a year. Doubtful with ubiquitous white gel coat from Jamestown Distributors.
There were a couple of small cracks and divots in that boats gel coat which had received no resin. We dabbed some gel coat filler in those cracks. Most of those gel coat over gel coat repairs finally set up. A few still have not. WTF?
Maybe, just maybe, gel coat over epoxy resin is simply a bad idea no matter how well cured and cleaned.

Any more educated guesses?

Any idea what to do with the 14 ounces of gel coat remaining? If it is still tacky tomorrow I could mix up another batch with a few additional drops of catalyst and recoat it.

 

[Glenn MacGrady]

I have no experience with this topic other than to relate my aesthetic opinion of a canoe hull that's been entirely re-gel coated.

I saw a Curtis Dragonfly in the Hemlock Canoe shop several years ago that had just been entirely re-gel coated by Dave Curtis, who probably has hand laminated more composite canoes than anyone on the planet. The gel coat did not look anywhere near as nice as a new canoe that's had gel coat sprayed and cured in the mold. In fact, it looked no better to me than paint. I asked Dave why paint on gel coat instead of paint. He simply said that's what the owner wanted.

I have no idea what kind of resin that '80's canoe was made with, but Dave surely does.

 

[BWCA66]

I've always used a duratec additive to get gel coat to air harden. That works great but is expensive. You could tape saran wrap over it to cut off the air.

 

[Guest]

Gel coat after 48 hours in a warm shop and gentle direct head. Still tacky.

Screw it, I need to shop space, and do not need to continue keeping the shop that toasty warm. If it has not set up yet I doubt it ever will, that boat goes outside to make space.

Should I try to remove the still tacky gel coat? Acetone maybe? It is gonna rain and I do not want it to ooze white gel coat down onto the red part of the hull.

 

[BWCA66]

Gel coat after 48 hours in a warm shop and gentle direct head. Still tacky.

Screw it, I need to shop space, and do not need to continue keeping the shop that toasty warm. If it has not set up yet I doubt it ever will, that boat goes outside to make space.

Should I try to remove the still tacky gel coat? Acetone maybe? It is gonna rain and I do not want it to ooze white gel coat down onto the red part of the hull.

Yes, acetone should take it off or you could tape plastic over it to cut the air off and see if it dries.