Cedarstrip/epoxy over a fiberglass sailboat hull?


LOVES Wooden Canoes
I have a 30-year old 14' fiberglass Holder 14 sailboat with hard chines and pretty flat sides above the waterline. Rather than refinish the sides and transom of the old hull, I'd like to add 1/4" x 2" cove-and-bead mahogany strips set in epoxy and edge-glued with epoxy on the sides and transom. I'll then cover the wood with fiberglass and epoxy, finishing up with several sprayed coats of automotive clear coat. The hull bottom will receive 2-part epoxy paint below the waterline.

I'm thinking of using a power brad nailer and driving 1" brads deeply set into the mahogany strips and through the fiberglass hull. I'll leave them in when I glass over the strips.

Has anyone had experience with laying strips like this onto a fiberglass hull?
That's a pretty strange way to rebuild a boat. You already have a stand-alone fiberglass hull, so the 1/4" thick strips aren't going to add anything structurally. Same thing is probably true with the fiberglass sheathing, unless you plan on dragging it over a lot of rocks on its side. Nails from a gun (or even without the gun) have little or no holding power when driven into or through fiberglass, so they probably wouldn't even do a particularly good job of holding the pieces together or down tight until the glue dried. They'll just make a lot of holes in the hull and little fractured spots.

I really think the gluing-wood-to-fiberglass thing will prove to be a mistake and most likely end up in the dumpster, but if I had to try it, I'd use veneer, probably sliced, rather than peeled (it curls less and there isn't much reason to make a fiberglass boat look like it's made from plywood) and 1/16"-5/32" thick. There is no need for 1/4" thick wood and its thickness just adds more problems to an already problematic solution. I'd think about applying it with either epoxy or maybe 5200, but wouldn't expect nails or staples to hold it down properly. It might be do-able with lines of small screws, or maybe even one of the catayized contact cements used for building sportboats and river rafts. After it's applied, the wood could be epoxy-coated and/or fiberglassed. As mentioned, the boat doesn't need the glass for strength, but if there is any give in the adhesive (5200 or Contact cement) the cloth might help prevent cracking (though probably not forever). Your auto clearcoat is only as good as its UV absorbers. If they aren't excellent, the sun will kill the epoxy in short order. Real marine varnish made specifically to protect epoxy might be a better bet.

When you start comparing this whole scenario to starting with a real boat plan, new materials, proven techniques and building a real wooden boat, it seems like a pretty crazy idea, and most likely not the best one you ever had. I have rebuilt several fiberglass sailboats with painted exteriors and they came out pretty nice. That type of restoration would certainly be a possibility for your Holder, and even though it's not woodworking, it's fun to see an old boat come back to life. I bought this little green one on the trailer for $600. It was all chalky, had been full of water at some point and had holes in the bottom where the trailer pads had broken through to let the water (and weight) out, gel-coat blisters and was pretty much trashed. After restoration, it was a very neat little boat and sanding, patching, fairing and repainting is all pretty straightforward with predictable results and no questionable techniques involved.

The wooden boat was originally planked with 3/4" cedar and painted. The cedar was constantly checking and I got tired of repainting the cracks, so I veneered it with mahogany, alcohol-stained it, epoxy-coated it and varnished it. The difference between that and your proposed project is that it's pretty easy to epoxy veneer to cedar and hold it in position while the epoxy sets up and then seal it properly so that it is structurally sound and will last. I don't believe you'll find the same thing to be true when trying to apply wood to a fiberglass hull. Having done both fiberglass restorations and laminating new wood over old wooden hulls as well as having a pretty good grasp of the materials and techniques involved, there is no way I would try what you're proposing and expect it to work well or last long. I'd rather either restore it back to being a nice fiberglass sailboat, sell it and use the money to build a new boat, or borrow the Holder rig and hardware and build a new wooden hull to use it on. It would be easier and most likely last a lot longer.


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Auto Clearcoat UV Protection

Great info, and everything you note is, I'm sure, true. But I have this clear 14' x 2" mahogany, and I have this 14' sailboat with very little money invested in it, and I'm too stupid to listen to good advice, so....

The brads hold in the fiberglass surprisingly well on a test I did in an unobtrusive place on the hull. But they are only to hold the mahogany until the epoxy sets, so I'd gladly try some other way to hold the strips on. I'm intriqued by your mention of 5200. Is it a contact-type adhesive?

I'm in my third year of a test of sprayed automotive clearcoat as a protective topcoat for epoxy, and so far it looks very positive. I glued up some 1 x 1 cherry strips for the tailgate on my utility trailer. After 6 oz fiberglass cloth and MAS epoxy covering, a body shop sprayed on several coats of PPG clearcoat with an additive called Flex added to the mix to increase—what else—flexibility.

The trailer sits outside in the sun 24/7/365. I intentionally park it with the tailgate facing south in my yard to maximize sun exposure. So far, after three years, I can see no difference in the coating from the day it came back from the body shop. Still has its high gloss and there are no signs of epoxy degrading under the coating.

I don't think this would be the case with 5 coats of even the best spar varnish, and I'd be looking at recoating soon, if not earlier.

The clearcoat can be sprayed on with successive coats at 30 minute intervals as it flash-dries very quickly. Each coat builds up a 5-mil film, nearly twice as thick as spar varnish. The shop did four coats on my tailgate for a 20 mil thickness.
5200 is a 3M marine adhesive calk that sticks stuff together like you wouldn't believe. There have been folks in some of the wooden speedboat groups using it for wood bottom replacement, but I don't know an awful lot about the process. If you do a search for "5200 Bottoms" you might find some info.
I still think the nails are what's most likely going to kill your project. It's just one of those things that you don't do to a fiberglass hull and get away with. Holders are somewhat notorious for gelcoat blistering and punching a bunch of holes in the glass that you can't properly seal from both sides is just asking for serious trouble down the road. The only logical way to bond wood to a fiberglass hull is with some adhesive that has a high enough initial tack that you can do it without the huge liability that all those holes create. If it's a cored construction in places (which it well may be) that only makes the perforations more dangerous. Not having tried something like this, I can't tell you which adhesives stand the best chance of sealing the underside of the wood, sealing the holes or having enough initial tack to eliminate the fasteners. I could be wrong, but my money still says this project is doomed from the start and I'd be surprised if it survives more than a few seasons before it becomes so screwed up one way or another that it winds up in the dumpster. That's kind of a sad fate for a boat that could be properly restored and last for decades.

Sounds like your clearcoat is working OK. Just remember that UV absorbers over epoxy get used up as they do their job and need to be renewed on a fairly regular basis (before any damage starts to become evident, because by that time, it's too late). After three years of exposure, your trailer is likely due for recoating. It's pretty easy with all this technology to create situations where fixes initially look decent, but are relatively short-lived, especially if not regularly maintained. In many cases, letting them weather just a bit too much can create a scenario where you can no longer fix the problem, yet you can't get the stuff off to replace it without investing more work and money than it's worth.
Yeah, my T-Bird has about 2/3 fiberglass panels and is doing fine. But the thing protecting the fiberglass from UV damage isn't the clearcoat, it's the paint and primer under it, which is a superb UV blocker - not an absorber or filter, a blocker. Even without the clearcoat, the resin would be protected and the worst thing that would happen would be eventual paint and primer chalking. So unless you strip the paint and primer off of a Corvette and do some kind of clear finish, the fiberglass and resin will never suffer from UV exposure. Likewise, the easiest and longest-lasting way to prevent UV damage on an epoxy-covered boat is simply to give it a good paint job. In this case though, I believe we're talking about a clearcoat over clear epoxy over wood (otherwise, the whole restoration job doesn't make much sense). That's a very different story from an opaque painted finish. I'm sure auto clear-coats contain some sort of UV absorber, and it's probably a good one, but there aren't any available that last forever and the idea that you can hire somebody to blast a few coats over clear epoxy and you're set for the duration will most certainly eventually end in failure. Once the protection is used up (many of these work by converting UV to heat and allowing it to dissipate into the atmosphere and in the process the tiny absorber bits give their lives to protect the finish) you have as little as a couple hundred hours of UV exposure before the epoxy breaks down. If it's sitting outside in the sun, that's not very long.

I don't know why auto clearcoats have never made it big in the marine industry. Obviously, they aren't your typical backyard builder's coating because of the equipment involved, but neither are many of the Linear Polyurethane marine coatings, which are pretty common when money is no object and the applicator has the equipment to deal with their serious toxicity (which is much greater than most auto finishes - cyanide fumes, required pumped-in air supply etc.). If you want the best finish you can buy for a boat, they're usually it.
Jeez Pumpkin, you always seem to have some strange desire to make an argument out of everything. Oh well, if you insist....
My original statement was simply a warning:
"Your auto clearcoat is only as good as its UV absorbers. If they aren't excellent, the sun will kill the epoxy in short order. Real marine varnish made specifically to protect epoxy might be a better bet."

I didn't say that they didn't have good absorbers, I simply stated that he should be sure that they do before using them and that if they didn't that there are proven products that do for marine use. If you have a problem with that, then you don't know much about epoxy boat construction as it is a critical issue if you want any clear-finished boat to last.

Then I cautioned that clearcoat, even if it does have absorbers, has a UV lifespan, which is obvious by all the cars driving around where UV has burned through it and is now burning into and chalking the paint under it. I don't know what that lifespan is in terms of exposure time, but it's pretty obvious that it has one. Clearcoat primer? I'm not even sure that it exists, but it would have the same sort of UV absorbers and they would also have a limited lifespan. In any case, if what's under your clearcoat, or any other clear finish, happens to be epoxy resin and your finish has lost it's ability to block or filter UV your epoxy is going to be in big trouble in short order - and it's not just cosmetic damage, it loses it's structural strength. You probably haven't worked with epoxy long enough to see what UV can do to it, but it isn't a pretty picture. A lot of brands turn yellow, get gummy and break off like pieces of an art-gum eraser.

Auto finishes just don't seem to have ever caught on all that well in the marine market for some reason, but I hardly think it's due to some sort of conspiracy between the varnish makers and those who apply it professionally. If you've ever known any real professional boatbuilders, the idea that they could ever be that organized is laughable and competition is tough enough that if something provided a better finish, there would be plenty of folks using it and using it as a reason that their construction is better than the next guy's. Instead, that slot gets filled by two-part L.P. systems like Awlgrip, which are considered the top dog in the marine coatings industry. Perhaps there is something about auto paint that makes it less suitable for long periods of continual immersion, or the expansion and contraction that some boat hulls go through. Perhaps it scratches easier. It seems pretty tough on cars, as you mentioned, but we don't usually rub our cars on docks, pull them up on beaches or leave them submerged for a weekend or longer when we go on vacation. Whatever the reason for it's lack of popularity, it seems to be pretty prevalent among those who build and paint boats at any price level and the reason is bound to be more than just some silly conspiracy theory.

Will it fail in use? I don't know. How long is it good for as a protective UV blocker? I don't know, and you don't seem to either. I'd probably want to know these things before putting it on a boat and I'd certainly want to know them before attempting to protect epoxy resin with them - because the one thing that I do know is that if your protection fails, your epoxy fails.
Perhaps you would like to try that simple Google search and post your results. I actually did one, and the clear coat manufacturers and vendors are quite tight-lipped about just how much UV protection their products actually offer. A generalized statement like "extended protection from UV" for their premium grades seems to be about all most of them will say. Maybe you can find one that gives a more precise time frame.

I did find a few interesting things though. This one was from a custom auto painter:
"The other thing with clear, is that the quality ones(BASF, PPG, etc) can be very expensive. Cheap clear is characterized by chaulking and deterioration. The biggest difference between the inexpensive clears and the high quality ones is the amount of UV inhibitor that's present. Like most things in life, you get what you pay for. A quality clear is in the 250-300$ a gallon range, and up. Thats a complete setup with hardener, reducer, and the clear."

This one was from an epoxy manufacturer: who sells epoxy resins, epoxy sealers and coating systems to go over them.

I was surprised to learn from my suppliers that most clear coat products have very little UV protectors added to them (many have a "UV Package" in them that does have a small/token amount of UV protecting chemicals). I suspect it has to do with cost. When I had one of my formulators take our 2 part acrylic polyurethane clear coat (which I always just assumed, incorrectly, had UV blockers/absorbers) and add the maximum amount of UV blockers and absorbers to it, it added over 20% to the manufacturing cost of an already expensive, high end coating. While most car manufacturers won't admit it, the cost of applying clearcoat/basecoat finishes substantially reduces their cost to paint the car. How so? First, recognize that the most expensive ingredient in paint is the pigments. With single stage paint finishes a manufacturer would apply at least 4 to 5 mils of colored paint. Compare this to no more than 1 mil of colored paint that is covered with 1.5 to 2 mils of clearcoat. Doesn't take much to see they are saving money.

(His suggestion for the best finish for his personal clear-finished canoes and kayaks was actually to varnish over the epoxy and then use his ultra-UV fortified clear coat on top of that)

and this one came from a paint chemist:

Please allow me to provide some minor exterior finish Chemistry 101 from back in my days as a polymer scientist developing UV blockers in clear coatings for a 100% solids polymer company: UV protection in the best modern boat varnishes would a synergistic combination of two additives: Tetratraziole-based UV blockers and Hindered Amine Light Stabilizers (HALS). The best and largest supplier of these additives are from Ciba-Geigy (Five Year Clear mentions them on their website also), and both additives are deep yellow in color, yet crystal clear liquids, not milky (some will say that the milkiness of the varnish is the UV additives - not true). These additives are used in a 2 to 1 ratio together, where the overall formula will have at most (very expensive formula loading) 2% by weight Tinuvin (Ciba's brand name) 292 (HALS) and 1% by weight of any of the 400 series of Tinuvin tetratraziole UV blockers. (HALS do not block UV, but "mop-up" the excess free-radicals created from UV oxidation, while the Tetratraziole UV blockers absorb the UV light similar to opaque pigment, but are clear additives). This is the first dead giveaway to me of the effectiveness of any given clear marine varnish - How "yellow" or amber the coating is - the more yellow, the better UV protection. The Ciba additives are also very expensive, so you get what you pay for - i.e. if the varnish is cheap, it'll likely have very little UV protection, and vise versa (hopefully). This is highly dependent upon the elasticity of the given formula, though. You could have the most expensive, highest loaded UV blocking package in a given formula, but if the urethanes cross-link too tightly, you'll get brittleness and cracks. This is perhaps the advantage of the one-part varnishes that are tried and true, however it is possible to formulate 2 part, elastic varnishes quite well, and thats why they are also high-performance (they spray better, etc). All this is also dependent upon the mil thickness of the final coating - Too thin, and the sunlight easily penetrates past even the best blockers - too thick and you risk polymer shrinkage cracks. And one final observation - even the best UV protection in the best aliphatice urethane formula will eventually "extinguish" - which is chemist-speak for the "burning out" of these expensive UV blockers/HALS over the years. This is why you want to apply the maximum safe mil thickness, so that as the surface of the coating extinguishes, the sub layer is going to be "fresh"...

Interesting stuff, but it pretty much leads me back to my original statements - that your clear coat needs to be a good one with good UV protection and that at some point, it will wear out and need to be refreshed. When that point will come will most likely depend upon the quality of the product chosen and its abilities. Surprise, surprise.
Sorry to bring up the topic

Sorry for the mention of automotive clearcoat, as I didn't know its use was so controversial. I'm not much for expounding theory, so I just do what experience tells me works. And clearcoat surely works well in my limited three-year test as the photos show.

So far, the only possible downside I see to spraying PPG clearcoat with an HVLP gun is that you don't get the sensual pleasure that brushing spar varnish gives. But after brushing and wet-sanding the fourth coat on the fourth day, I've had plenty enough sensuality. I have better things to do with my time.


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I have a 30-year old 14' fiberglass Holder 14 sailboat with hard chines and pretty flat sides above the waterline. Rather than refinish the sides and transom of the old hull, I'd like to add 1/4" x 2" cove-and-bead mahogany strips set in epoxy and edge-glued with epoxy on the sides and transom. I'll then cover the wood with fiberglass and epoxy, finishing up with several sprayed coats of automotive clear coat. The hull bottom will receive 2-part epoxy paint below the waterline.
I thought this was going to go on to include, "Then pop out the glass boat and sail away in my new wooden sailboat!" I once almost bought a beat up Snark with the idea of doing the same but thankfully I decided it was too small a boat and too risky a plan.

Either way, I hope you keep posting your progress. Pics are always fun too.