Gel coat cracks
Moderator: Jim Walsh
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Doug Oliver
- Posts: 61
- Joined: Feb 13th, '05, 06:55
- Location: CD33 Lola
Bucks Harbor, Maine
Gel coat cracks
I have a 1982 CD27 and am thinking of moving up to a 33 or 36. Did Cape Dory get to a time when gel coat cracks were no longer a problem or at least where the problem was less? I have had no problem with moisture in the deck but still don't like the cracks. Thanks for any input.
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Doug Gibson
- Posts: 93
- Joined: Nov 6th, '07, 14:28
- Location: Sail Fish
'87 CD36 #147
SF Bay, CA
Gel Coat Cracks
Hi Doug -
I have a 1987 CD36 with a number of gel coat stress cracks on deck near cabin house wall or cockpit and in cockpit floor. My understanding is that its related to thicker than necessary gelcoat and designed radius where perpendicular surfaces come together. Boats exhibit a range in amount of cracking, so I think it's due to variability in gel coat thickness and perhaps stress boats have seen during use.
I have a 1987 CD36 with a number of gel coat stress cracks on deck near cabin house wall or cockpit and in cockpit floor. My understanding is that its related to thicker than necessary gelcoat and designed radius where perpendicular surfaces come together. Boats exhibit a range in amount of cracking, so I think it's due to variability in gel coat thickness and perhaps stress boats have seen during use.
Doug Gibson
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Troy Scott
- Posts: 1470
- Joined: Jan 21st, '06, 01:23
- Location: Cape Dory 36 IMAGINE Laurel, Mississippi
repairing gelcoat cracks
Doug,
I have a "1988" CD36, #152, built in late 1987. The gelcoat on the deck is very thick, and there was a lot of gelcoat cracking. The cracks ranged from long and more-or-less parallel or perpendicular to radiused areas like the cabin sides to deck area, to very short and closely spaced on large flat areas. Interestingly, there is/was no cracking on the topsides. I have learned that there are at least three contributing factors for this deck gelcoat cracking. The most readily apparent is that the gelcoat is considerably thicker than it should be. Mine is everywhere at least .060", and in some places more than .125"! The second factor is probably inaccurate catalyzing of the original gelcoat. The third factor is that when the decks were pulled from the mold they were probably stressed. On the bright side, I've never seen a CD with the gelcoat wearing through. This is a common sight on older, well used Catalinas.
I studied this problem a lot before I made my repair plan. I went so far as to talk to gelcoat manufacturers about what could have caused the gelcoat to do this. They pretty much all said the same things, which are the ones I mentioned above. The consensus was that if it was a catylyst ratio problem the resultant cracking would happen early in the life of the boat and then stabilize. Likewise for the stresses of mold release. Hopefully only one factor of the original three will continue to haunt me as the boat ages: that is the gelcoat thickness. I didn't try to thin it more than just slightly, because I didn't want to lose the nice original contours. I haven't noticed any additional cracking in the months since I finished filling and priming, so I feel pretty good about that. I hope no more cracks appear after I paint and launch the boat, but only time will tell.
I opened all the cracks with a small, round-ended carbide dremel cutter and then over-filled the little valleys with thickened epoxy. I did NOT use gelcoat, because I had observed that ALL of the cracks that had been previously repaired with gelcoat had reopened on at least one side of the repair, and sometimes on BOTH sides. After sanding this filler flush I followed with several coats of an epoxy primer on the whole deck. Then I sanded that really smooth. Next I will finish paint the deck.
I found only a little moisture in the balsa core, and none of it was related to the gelcoat cracks. One place, just inboard of the aft port cleat, had damp core because CD didn't seal the balsa where the Dorade (just inboard of the cleat) penetrated the deck. That's all fixed now. The other place was near the starboard end of the mainsheet traveler. Whoever installed the twist fasteners for the dodger didn't use any sealant on the screws where they penetrated the balsa. Of course the water found it's way in there too. That's fixed as well. I've been working to completely isolate the balsa from any possibility of picking up moisture. I'm not leaving any balsa or plywood within a 1" radius of any fastener or hole that penetrates the deck. The solid thickened epoxy I'm installing in place of the balsa provides much better resistance to compression. I'm also eliminating all the aluminum backing plates in favor of 1/4" or 1/2" solid fiberglass pre-cured laminate.
Doug, you can put up with non-structural gelcoat cracking. But, like you, I just hated the way it looked, so I felt I had no choice but to fix them. I did the repair the most positive way I could do it. But it was A LOT OF WORK. I knew when I was doing it that the Interlux folks insist that their 404-414 epoxy primer will fill these cracks, and that opening them and using a thickened epoxy filler is unnecessary. I am dubious of that idea, because I observed many cracks under the repainted nonskid when I sanded it. The Brightsides paint just bridged over the cracks and didn't fill them at all. Now, granted, the Interlux primer is NOT Brightsides, and the primer may actually fill cracks as advertised. I don't know because I haven't actually tried it. If the primer would work as advertised, I believe using it could be part of an easier and faster method. Having said that, I will say this based on my experience: If I were going to try to fix extensive deck gelcoat cracking using epoxy primer without first opening the cracks, here are the steps I would follow:
1. Thoroughly scrub the deck with TSP in water and a brush.
2. Thoroughly rinse.
3. Thoroughly dry.
4. Move inside.
5. From now until you have finish paint on the deck, use a clean pair of shoes only on the deck. Use another pair for walking about the shop.
6. Use a plastic bondo spreader or similar to work the primer into the cracks. Move the spreader across and parallel to the cracks until you're absolutely certain they're full. Try to make sure the boat is cooling rather than heating as the primer cures, as this will help draw it into the cracks. Overfill the cracks. Don't worrk about making it neat, just make sure the cracks are full.
7. Sand flush with the original surface.
8. Add additional primer here and there as needed, and sand again.
9. Prime the whole deck.
10. Sand the entire deck, this time with finer paper.
11. At this point you should be nearly ready for finish paint.
I feel good about the way my repairs have apparently worked (time will tell) but, having done this "the hard way" I would definitely try this easier, faster method if I had it to do again.
Good luck!
I have a "1988" CD36, #152, built in late 1987. The gelcoat on the deck is very thick, and there was a lot of gelcoat cracking. The cracks ranged from long and more-or-less parallel or perpendicular to radiused areas like the cabin sides to deck area, to very short and closely spaced on large flat areas. Interestingly, there is/was no cracking on the topsides. I have learned that there are at least three contributing factors for this deck gelcoat cracking. The most readily apparent is that the gelcoat is considerably thicker than it should be. Mine is everywhere at least .060", and in some places more than .125"! The second factor is probably inaccurate catalyzing of the original gelcoat. The third factor is that when the decks were pulled from the mold they were probably stressed. On the bright side, I've never seen a CD with the gelcoat wearing through. This is a common sight on older, well used Catalinas.
I studied this problem a lot before I made my repair plan. I went so far as to talk to gelcoat manufacturers about what could have caused the gelcoat to do this. They pretty much all said the same things, which are the ones I mentioned above. The consensus was that if it was a catylyst ratio problem the resultant cracking would happen early in the life of the boat and then stabilize. Likewise for the stresses of mold release. Hopefully only one factor of the original three will continue to haunt me as the boat ages: that is the gelcoat thickness. I didn't try to thin it more than just slightly, because I didn't want to lose the nice original contours. I haven't noticed any additional cracking in the months since I finished filling and priming, so I feel pretty good about that. I hope no more cracks appear after I paint and launch the boat, but only time will tell.
I opened all the cracks with a small, round-ended carbide dremel cutter and then over-filled the little valleys with thickened epoxy. I did NOT use gelcoat, because I had observed that ALL of the cracks that had been previously repaired with gelcoat had reopened on at least one side of the repair, and sometimes on BOTH sides. After sanding this filler flush I followed with several coats of an epoxy primer on the whole deck. Then I sanded that really smooth. Next I will finish paint the deck.
I found only a little moisture in the balsa core, and none of it was related to the gelcoat cracks. One place, just inboard of the aft port cleat, had damp core because CD didn't seal the balsa where the Dorade (just inboard of the cleat) penetrated the deck. That's all fixed now. The other place was near the starboard end of the mainsheet traveler. Whoever installed the twist fasteners for the dodger didn't use any sealant on the screws where they penetrated the balsa. Of course the water found it's way in there too. That's fixed as well. I've been working to completely isolate the balsa from any possibility of picking up moisture. I'm not leaving any balsa or plywood within a 1" radius of any fastener or hole that penetrates the deck. The solid thickened epoxy I'm installing in place of the balsa provides much better resistance to compression. I'm also eliminating all the aluminum backing plates in favor of 1/4" or 1/2" solid fiberglass pre-cured laminate.
Doug, you can put up with non-structural gelcoat cracking. But, like you, I just hated the way it looked, so I felt I had no choice but to fix them. I did the repair the most positive way I could do it. But it was A LOT OF WORK. I knew when I was doing it that the Interlux folks insist that their 404-414 epoxy primer will fill these cracks, and that opening them and using a thickened epoxy filler is unnecessary. I am dubious of that idea, because I observed many cracks under the repainted nonskid when I sanded it. The Brightsides paint just bridged over the cracks and didn't fill them at all. Now, granted, the Interlux primer is NOT Brightsides, and the primer may actually fill cracks as advertised. I don't know because I haven't actually tried it. If the primer would work as advertised, I believe using it could be part of an easier and faster method. Having said that, I will say this based on my experience: If I were going to try to fix extensive deck gelcoat cracking using epoxy primer without first opening the cracks, here are the steps I would follow:
1. Thoroughly scrub the deck with TSP in water and a brush.
2. Thoroughly rinse.
3. Thoroughly dry.
4. Move inside.
5. From now until you have finish paint on the deck, use a clean pair of shoes only on the deck. Use another pair for walking about the shop.
6. Use a plastic bondo spreader or similar to work the primer into the cracks. Move the spreader across and parallel to the cracks until you're absolutely certain they're full. Try to make sure the boat is cooling rather than heating as the primer cures, as this will help draw it into the cracks. Overfill the cracks. Don't worrk about making it neat, just make sure the cracks are full.
7. Sand flush with the original surface.
8. Add additional primer here and there as needed, and sand again.
9. Prime the whole deck.
10. Sand the entire deck, this time with finer paper.
11. At this point you should be nearly ready for finish paint.
I feel good about the way my repairs have apparently worked (time will tell) but, having done this "the hard way" I would definitely try this easier, faster method if I had it to do again.
Good luck!
Regards,
Troy Scott
Troy Scott
Time will tell
I was disappointed to find many of the cracks I repaired using the same method Troy described re-appeared after a few years, but much smaller than they were. Perhaps it has to do with uneven stress in those locations and /or inadequate structure, I'm not sure. Keep in mind many of these vessels are 30 + yrs. old and some imperfections will have to be allowed. I'd be interested to hear of others who had success over time....and if different methods were used.
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Honda airport history
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Honda airport history
Last edited by Ron M. on Feb 11th, '11, 05:53, edited 1 time in total.
Gel Coat Cracks
I have a 1987 CD 30MkII, and the boat had a zillion gel coat cracks when I bought it in 2005. I consulted with a local yard and the consensus was; the only way to permently fix the problem was to strip the gel coat. This we did, cabin top and sides, deck, and cockpit. All areas were then algripped. Big job, and expensive, but the boat looks like new.
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Troy Scott
- Posts: 1470
- Joined: Jan 21st, '06, 01:23
- Location: Cape Dory 36 IMAGINE Laurel, Mississippi
rounding valleys (sounds like the title to a novel)
Lee,
I used a rounded tipped cutter, but i didn't bevel the edges of the valleys. In retrospect, from an engineering standpoint, that probably would have been better. Another thing I forgot to mention is this: I learned in my research that gelcoat is not just colored resin. It does have a little structure, in the form of tiny milled glass fibers. For this reason I added a very small amount to the mix I used to fill the cracks. If you use too much the filler will be too hard to sand, and if you use too little the filler might be brittle.
king11
I'm sure that stripping the gelcoat away would be the ultimate solution. I would not remove all of it, but I would sand until the gelcoat is translucent here and there. However, this approach is a LOT more involved. Many areas would require significant "sculpting". For example: in the area near the forward, outboard sides of my coamings where they meet the house sides and the deck, the shape is very complicated. I think it probably didn't come out of the mold well, and I discovered a lot of filler there. This would present a quandary to you or to the boatyard guys. Do you sand away all the deep filler along with the gelcoat? If so, what do you replace it with? Also, what about the gelcoat where it meets the toerails? You would have to either remove the toerails , sand the gelcoat away and then reinstall them, at which point they would no longer fit...., or if you didn't remove the toerails you could taper the gelcoat away from the toerails, which would of course leave the gelcoat it's original thickness near the edge of the toerails, which leaves the potential for future cracking... When I was deciding what to do about the cracks, the notion of losing the carefully sculpted original shape was a huge potential can of worms for me. For this and other reasons I decided to keep the original profile. As I mentioned, only time will tell if this was a mistake. If it was the wrong thing to do I'll know in a few years. Maybe I'll be wealthier then and the second refit could include removing the gelcoat, replacing the teak with everlastingly beautiful faux teak, a tall carbon fiber rig, a hybrid electric auxiliary, a bigger air conditioner, lithium ion batteries and a hard dodger.
I used a rounded tipped cutter, but i didn't bevel the edges of the valleys. In retrospect, from an engineering standpoint, that probably would have been better. Another thing I forgot to mention is this: I learned in my research that gelcoat is not just colored resin. It does have a little structure, in the form of tiny milled glass fibers. For this reason I added a very small amount to the mix I used to fill the cracks. If you use too much the filler will be too hard to sand, and if you use too little the filler might be brittle.
king11
I'm sure that stripping the gelcoat away would be the ultimate solution. I would not remove all of it, but I would sand until the gelcoat is translucent here and there. However, this approach is a LOT more involved. Many areas would require significant "sculpting". For example: in the area near the forward, outboard sides of my coamings where they meet the house sides and the deck, the shape is very complicated. I think it probably didn't come out of the mold well, and I discovered a lot of filler there. This would present a quandary to you or to the boatyard guys. Do you sand away all the deep filler along with the gelcoat? If so, what do you replace it with? Also, what about the gelcoat where it meets the toerails? You would have to either remove the toerails , sand the gelcoat away and then reinstall them, at which point they would no longer fit...., or if you didn't remove the toerails you could taper the gelcoat away from the toerails, which would of course leave the gelcoat it's original thickness near the edge of the toerails, which leaves the potential for future cracking... When I was deciding what to do about the cracks, the notion of losing the carefully sculpted original shape was a huge potential can of worms for me. For this and other reasons I decided to keep the original profile. As I mentioned, only time will tell if this was a mistake. If it was the wrong thing to do I'll know in a few years. Maybe I'll be wealthier then and the second refit could include removing the gelcoat, replacing the teak with everlastingly beautiful faux teak, a tall carbon fiber rig, a hybrid electric auxiliary, a bigger air conditioner, lithium ion batteries and a hard dodger.
Regards,
Troy Scott
Troy Scott