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Spider Cracks in Gelcoat - Moderated Discussion Areas Spider Cracks in Gelcoat Author Topic: Spider Cracks in Gelcoat rtk posted 06:04 PM ET (US) 17 bodega relays his frustration in the lack of good information available on the cause of 'spider cracks', or 'stress cracks' in classic Boston Whalers. It is a great question as to why they occur. We have this awesome boat that just cannot take enough of a beating, but the gelcoat in some spots seems to 'craze', or 'spider web'. I think the question, or topic even evolved to 'quality years' of Boston Whaler manufacturing. There are so many reasons why gelcoat developes spider cracks.
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It is very hard to pinpoint the cause to one finite reason because they occur on any fiberglass boat for very different reasons. As we all know, even the best built and well designed fiberglass boat flexes and moves a bit while underway or docked.
Gelcoat is a marine finish that cures hard just like polyester and epoxy resin. The gelcoat is primarily a cosmetic coating, it has no structural strength on it's own, just like epoxy or polyester resin.
The very basic reason for stress cracks in a gelcoat finish is the hull or surface that the gelcoat is bonded to flexed or moved an amount beyond the point that the gelcoat can flex, so it just cracks, because the gelcoat has no structural bearing attributes. A fiberglass layup that is too wet, or has too much resin will crack also. The resin does not bear strutural loads well either. It is the 'right' proportion of resin an fiberglass that gives the greatest strength.
So, if there is spider cracks, there are typically two reasons. The gelcoat was applied too thick at an area that does flex. Gelcoat will tolerate a bit of flex. But as the coating gets thicker, the less it will tolerate flex. The underlying fiberglass structure is not adequate, and the gelcoat cracks due to insufficient laminant layup or structural support during the molding process to support the gelcoat. The only way to know the cause of the stress crack is to grind along the stress crack with a dremel type tool until you hit fiberglass.
Grind the cracks out and pay attention to gelcoat thickness and the general binding of the gelcoat to the fiberglass layup. Also look for failure in the fiberglass. The problem with opening up stress cracks and repairing them is that it will more than likely be a cosmetic problem due to excessive gelcoat. Making a repair that will match, and will not crack again, will probably look worse than the original stress crack. I really don't think that a vast majority of true stress cracks alow water into the laminate. I do think that most stress cracks are a minor cosmetic problem. Now on a real old classic don't confuse stress cracks in the gelcoat with 'crazing' of the gelcoat.
I think most of the reports of 'cracked' or 'crazed' gelcoat on 30-40 year old hulls is ultraviolet rays from the sun damaging the gelcoat over time. To sum up, the only way to determine the cause of a stress crack, especially a minor one, is to grind the gelcoat off to evaluate the structural integrity of the fiberglass substrate. Usually it is not a productive action in grinding them out, filling and re-gelcoating the area so you do not see the cracks. Hope this helps Steve.
It is one of those things with boats that you will not know the cause of until you start grinding, absent a major gore in the gelcoat. If you have the San Andreas fault in the gelcoat you know you have problem, and water will be getting in there. Very fine lines here and there and there is probably very little if any water gettting down to the glass. Rich elaelap posted 06:36 PM ET (US) A simple solution for an otherwise sound hull, which I know won't please everyone, is Line-X or one of the similar brands. I know, I know.I guess it's a shame not to restore every 'old blue', at least for some of you.
I'd have no hesitation at all myself, especially if it led to a new life of heavy use for an old, heavily-spiderwebbed Whaler rather than neglect or abandonment. I've seen several Line-X'ed BWs which look great-Sierra's comes immediately to mind, as does Alex/alkar's blue-hulled (painted, not gelcoated!) beauty. I've seen a bunch of commercially-used Whalers with their interior hull entirely covered with Line-X-type coating, and IMO it often looks great and appears to be very utilitarian. I understand Steve/17 Bodega's frustration, since I owned his Katama before he did.
What a sweet boat with a sound hull; what a great ride; what surprisingly strong seakeeping ability for a light 16 ft skiff; but what a lot of annoying, surface-level spiderwebbing on her 35-year-old blue gelcoat. I've told Steve that if I had kept her, LooLee3 was heading for an interior Line-X treatment for sure. Tony Binkie posted 08:14 PM ET (US) I`ve worked on a lot of old hulls, Boston Whalers and others, and it seems the the Whalers have more than their fair share of spider cracks in the deck areas. I asuume this is because the laminate is much thinner on the Whalers than other boats that don`t rely on a foam interior for much of their strength.
I think Line-X other other cover up stuff only depreciates a boat. Better to sand the spider cracks out and repaint or re gell coat.
Loafer posted 08:47 PM ET (US) Right now I’m starting to attack some large areas of gel coat cracking in my ’74 project Revenge. In what I’m seeing, it looks like more the case of over thickness in the gel coat then flexing in the underlying laminate.
Some places the gel coat is actually flaking off and it’s over 1/8 inch thick. Surprisingly, much of the damage is under fittings, such as under the step plate on each bulwark, or under the rail stanchion plates. It looks like heat from sunlight on the metal fitting may have caused the cracking. Another place is under the glass near the helm where heat seems to have been concentrated (?).
In many cases, the gel coat has curled up like old paint and separated from the underlying layers. Where it’s delaminating or flaking, I’m grinding it off.
Where it’s just cracked, I’m using an old “church key” (Burgermeister seems to work best, although a Carlings Black Label might do in a pinch) to vee out the crack. I find this low tech approach works better than a Dremel tool for a couple of reasons; first it’s much easier to control, the point of the can opener naturally follows the crack and you don’t all gow up the surface where you didn’t intend to. Second, it’s much faster, especially on small cracks that haven’t started to “potato chip.” Happy winter projects to all and may your weather soon be warm enough to apply resin. Loafer 17 bodega posted 09:01 PM ET (US) Thanks Rich for bringing up the topic. It is a pet peeve of mine due to my aging hull.
High Sierra has done a fantastic job on his 15 footer with the 'Line X' type product, but I would sure love to stick with the vintage blue if possible. It's like a cheesey 50's bathroom and I just love the tacky throw back to the era when all bathroom tile in the suburbs resembled this color. Fact: Spectrum paste, gelcoat, and polyester resin (cured slow and fast) just cracked right through again, as did marine tex, marine fix (goop product) and several other epoxy type products. I would love to see photo links to work like Keltonkrew on different spider crack remedies and their costs and labor needed. What is the skill level required to make such an upgrade? I'm not so concerned about cosmetics, I just don't want my hull to accumulate water as it sits in the rain or takes on water for any other reason.
Deepwater posted 09:36 PM ET (US) i had spider cracks allong the insides of my 17 mon and around the aft well and anchor locker, i had my local rino dealer cover the whole deck for me,around $200+,no more spiders and its antiskid and it comes in lots of diff colors elaelap posted 09:54 PM ET (US) Alex's green-hulled beauty. Runpasthefence posted 01:56 AM ET (US) My father has a 1976 15' in the process of a re-paint. The gel was in dismal condition, and we've been in the process of doing an awl-grip paint job on the boat for the past month or so. I hadn't really considered the line-x option until recently. The boat is primarily used with 4 dogs aboard, lots of sand, water, etc. I'm worried the awl-grip won't be able to put up with the abuse that 4 goldens and my parents can dish out.
Do we sound like candidates for Line-X or a similar product? I'd love to hear some opinions/experiences? How well does the material grip when walking on it, esp. Thanks a lot guys. Goinboatn posted 09:22 AM ET (US) I own a Line-X shop in Fl. The product works great on boats for keel guards, interior floors, etc.
I built a rear deck for my montauk and encased it with line-x. Also Line-X can be painted FYI. My deck is matched desert tan. I made new cooler tie downs, rps seat bottom, pate fuel tank stop all sealed with line-x so they will never rot and never need to be replaced!
All you have to do is cut and carve your own replacements and take them by your local line-x guy to be sprayed probally while you wait. Dries in 3-6 seconds aahhh instant satisfaction-why I like it! New World Coatings SpongeBob posted 10:07 AM ET (US) I have noticed over the years and boats that almost all spiderwebbing or crazing of a boats takes place on the topsides (deck, gunnles, center console and so forth).
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Very seldom is it found on the sides or bottom of the hull. As RTK states there are several sturctural issues that may lead to this problem.
However I believe the environment plays a large role. On boats that are covered or are stored inside (not just for the winter but after each use) you find very little cracking or crazing. I live in probably one of the harshest environments for a boat, saltwater and the SW FL sun. Of the two I believe the sun does the most damage if left to do it's thing.
Every day a boat left in the sun goes through a heating and cooling cycle, with associated expansion and contraction. Thousands of cycles over the lifetime of a boat and somethng is bound to give. The weakest link is the gel coat (exagerated by the structural issues that RTK mentioned) and the result is cracking in varied forms. Keeping a boat clean and waxed will help. If the gel coat is allowed to degrade the process seems to hasten. Keeping the boat covered eliminates it almost entirely.
Yes I have seen boats that have been covered with cracks but much fewer in number than those without covers. I don't pretend to be an engineer (I'll leave that to my son) just an observer. It would be interesting to compare boats used and stored covered up north with those left to fend for them selves down here.
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