Tiny Cracks in Fiberglass

Craven Moorehead

Curious about Wooden Canoes
Hey there, I just picked up a Stowe Canoe with cedar and fiberglass construction and while the hull is in pretty nice shape with no leaking there is some minor cracking, like very fine spider web looking cracks.

I'm new to working with fiberglass so i don't know what is a problem and what isnt and how to fix etc.. but i do know that the previous owner had used marine paint to try and cover some of the cracks :rolleyes: and had coated the gunwales in some kind of Marine grade varnish.

I'd really like to clean this boat up and make it sparkly..I just don't know where to start. help please?:D
I did some more research and it looks like the cracks arent in the fiberglass but in the Gelcoat.

What i need help with is the Gelcoat. It appears that the Gelcoat was probably not waxed for many years and is beat by the sun and has some crazing and spider cracks. Can anyone point me to a resource to help me refinish the gelcoat please?

maybe now that i've got the problem right I can get an answer to point me there ;)

The Stowe Canoe Company became part of the Mansfield/Allagash Canoe Company and I don't believe they are in business any longer. The gelcoat is a polyester resin product and if you check with local marine stores or do a search for the manufactures like americanmarine supply.com they have products that can fill these cracks but ultimately, you may have to paint it.

Good luck,


PS, don't use epoxy for this repair...
:) I have one also.....Mine also developed over the years the same spider webs in spots and some fine cracks here and there...I am in the process of 440 sanding it down right now...A friend of mine has suggested I use a special 2 part primer that is used for priming motor vehicles before painting..This primer is a filler and then is to be sanded all over before painting...I am having a special color mixed to matched the original STOWE stock green...
By the way....the ORIGINAL Stowe canoe company became Tubb Snowshoe company ....The company that bought the molds became Mansfield becasue the origiinal Stowe was called the "Mansield" model in the 13' one.....They became Tubb snowshoe company becasuse there was more demand for the snowshoes and last year K-2 who had bought them out closed shop , letting 21 people go, and moved to some foreign country where they can get cheap slave labor!
Does your emblem on the side say STOWE and the under that in small letters..."Stowe Canoe Company, Stowe, Vermont?B]
Why not use epoxy? Epoxy sticks far better to cured polyester resin or gel coat than more polyester resin or gel coat ever will. Epoxy is more controllable, easier to modify with fillers for specific tasks, easier to apply and much less prone to shrinkage. You can certainly fix damaged polyester gelcoat with more polyester gelcoat, but to do it well or cover anything other than a small area, you need a lot of expensive equipment that most people don't have sitting around in their garages unless they happen to be in the fiberglass boat business. You can re-skin a fiberglass hull using epoxy, wind-up with a better, more durable result and the only tools needed are a roller and a $50 random orbit sander and a can of good marine enamel to top it off.

Gelcoat is a mixture of polyester resin, various pigments and cheap filler (usually talc). It has so much filler in it that it's not even particularly sticky (run into a dock with the stem of a fiberglass canoe sometime if you want to see how poorly it really sticks to the laminate underneath). It also isn't very flexible (again because of the high percentage of filler). The thicker it is, the deeper the gloss and shine on the hull, but the weaker and more brittle the gel coat layer is. The sun doesn't generally cause spider cracks. It's the unstable nature of the polyester/fiberglass hull under the gelcoat and it's tendency to shrink slightly over time that cracks the gel coat. All that filler won't allow the gel coat to shrink as much as the hull and the gel coat fractures. You can also get spider cracks from impacts. Again, it's the inability of the gelcoat to flex with the rest of the hull that causes it to fracture around the impact area and hulls with nice, thick, shiny layers of gel coat are the most likely to crack.

A coat of wax might remove some oxidation and make your old hull look shiny for a while, but it's not going to prevent spider cracks or have any long-term benefits for hull durability other than provide a very temporary and minor boost in UV resistance, at least until the wax has deteriorated. Luckily, these cracks are seldom of any structural concern. The gel coat isn't adding any strength to the hull and the laminate under it is already plenty sufficient to keep water out. You can cover an entire hull with spider cracks and it still won't leak.

The Fix - Small areas using matching polyester gel coat - sand down deeply into the cracked area. You may not need to sand all the way down to the bottom of the cracks or down to cloth, but you need to go deep enough that they are much smaller. Gelcoat can be brushed on or sprayed with a small "Prevail" canned spray system (marine suppliers). After curing, you wet-sand with successive grits, feathering out the patch into the surrounding area and finally buff it. If you have a power buffer, sanding up to about 600-800 grit is usually plenty. If you will be buffing by hand, working your way through the grits up to about 2000 grit is needed to really get nice gloss. A google search for gel coat repair will usually get you several step-by-step articles with photos which go through the process. This type of repair will work on small spots, up to about the size of a dinner plate. If you have bigger areas to fix, you really should have real spray equipment and power sanders to do the job efficiently. It's absolutely possible to re-gel-coat an entire hull, but it's an awful lot of work and isn't a job for amateurs.

Alternate Fix - full hull with paint finish - (if more than just a couple small areas are damaged, this would be more efficient). Again, sand the gel coat fairly heavily and down deep into any cracks. Then using a foam roller, roll on a minimum of three coats of epoxy resin (five or six thin coats would be better). You need about 10 mils of thickness to give you some cushion for sanding. Once the resin's cured, get out the sander (random orbit is the easiest) and sand it smooth using 80-100 grit paper. That leaves a pretty nice tooth for the enamel that will come next. You can use primer if you want, but it really doesn't do much over epoxy. Paint the hull with two or three coats of enamel and you're done.

Unfortunately, paint won't really fill spider cracks. Most of it just sits there, bridging the crack, which will then start to show through, so if you really want to get rid of them they need to be sanded down pretty far and the area filled with some sort of resin, gel coat or resin/filler powder mixture. Any way you slice it, it's a fair amount of work, so make sure the boat's worth it to you before diving in. Repairing one area also doesn't make the hull immune from future cracks elsewhere. Epoxy coating is less prone to allowing future cracking than just spot-patching the bad areas, but if the boat has thick gel coat, it still may eventually crack to some extent and the thin epoxy coating may not be able to stop it.

No canoe pix handy, but this is a fiberglass sailboat which had lots of spider cracks and some gel coat blisters. I re-coated, filled and painted as mentioned above using a roller to apply resin and paint and a $50 Porter Cable random orbit for the sanding -all done out in the driveway.


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:) Nice job Todd!.....That 2 part primer I am getting this week does have epoxy as the second part...The body man friend at the local body shop tells me that as I sand and smooth the gelcoat I can keep re-appling "as needed" in areas that need filling and that all "blems" will disappear...
Keep in mind as well that it's often easier to take a round or V-shaped Dremel bit and widen a hairline crack into a small trench and fill that, than it may be to get filler-stuff to penetrate down into a really narrow space. You could actually do this to an entire spider crack and then gelcoat it if you had the patience to sit there and dig all those trenches. It's also worth remembering the "dime rule" for filler. Fills will obviously usually feather out at their edges, but if you can keep the bulk of the fill about as thick or little thicker than a dime, after sanding, they tend to be more stable and less prone to popping, peeling or otherwise failing.
OK...strike my statement on epoxy, after seeing Todd's pic I'm convinced. I tried this a few years back on a badly neglected Mad River "Slipper" and when it failed, I was told by the epoxy mfg., that it was not compatable with polyester...more like a poor prep job by me! Anyway, ended up doing the job with 3M Marine surface filler followed by Imron automotive paint...turned out great.

Wow Todd thats great work on that Boat, thats the kind of shine i'm looking to get for sure. Do you wax the hull to get it that shiny or do you only do that on gelcoat?

Thanks for the replies guys, this has given me alot of idea on how to approach this....after I do some paddling ;)

Any suggestions on applying a finish to the gunwales? varnish? urethane(sp?) :dunno:

and should the seats be coated too?
Craven Moorehead said:
Any suggestions on applying a finish to the gunwales? varnish? urethane(sp?) :dunno: and should the seats be coated too?

Stick with a high quality traditional marine spar for the best UV protection. Sand well, start with thinned (50%) coat of varnish, sand with 180 0r 220, 70% varnish coat, sand, another 70% coat, sand then one or 2 coats of 90-100% varnish.

The PolyUrethane tends to bubble and peel - I don't know about the ones listed as "Exterior" - I'd stick to spar.
No, it's not waxed, it's just good paint. At the time the photo was taken the paint job was already two or three years old and the boat had been sitting outside year-round with a cockpit cover, but nothing covering the hull. It's Interlux "Brightside" enamel (their stock dark green mixed with a little bit of black to darken it even more). I'd actually sold the boat a year or so earlier and it was over here getting some work done on the sails and rig and I decided to give it a bath and get some digital photos of it.

You need to be very careful with waxes and polishes on any boat that you paint or intend to paint. Many (especially those "miracle" car and boat polishes that you see advertised) contain silicone, which can soak into the finish and make paint coverage and adhesion a major nightmare. Wax, if used, should just be icing on the cake. If the finish underneath doesn't already look really good, waxing it isn't likely to make it much better and won't generally last long enough to be considered a serious part of the process. If you do want to wax the hull, you might want to look at places like Target (automotive dept.) for a bottle of Zymol (about $12). It's a light blue, liquid cleaner/wax that is superb stuff and doesn't contain anything that can't be removed when it comes time for paint touch-ups or repainting. Marine stores also often carry 3-M "One-step" cleaner/wax which has a little bit of polishing compound in it to shine-up dulled surfaces. It's good stuff and silicone-free.

On wooden gunwales, I generally use "Captain's Varnish" (marine stores) but there are plenty of other high-quality marine varnishes which contain healthy amounts of UV absorber for maximum lifespan. Cheap varnish really isn't much of a bargain when you have to clean up the mess it leaves when it fails, so you might as well use a real marine-quality varnish from the start.
1938 Popular Mechanics Canoe Plans Wanted

This is my first post and I hope it is in the right section of the WCHA forum.

I am seeking copies of the 1938 Popular Mechanics Canoe plans. There was a time when the WCHA offered copies of these plans, as well as an article (by a member?) that gave additional information about the plans. I just learned that the WCHA stores no longer offers these copies.

I would love to reimburse anyone their copying expenses for copies of this article.

Please email me direct at 'stephenpdean "at" yahoo "dot" com', using the conventional email address protocol and please make the email Subject read: "1938 Plans" so I don't delete unfamilar email addresses. We can exchange mailing addresses and other info as required.

Thanks for all the advice folks, you all are an awesomely knowledgeable bunch :D

I'll be back with some pics when its time to do the refinishing, but right now since there's no leaks and its hotter than the very blazes i'm going cruisin :cool:

THanks again folks,