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Old 08-05-2015, 14:28   #1
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Repairing deck gellcoat stress cracks

Hello fellow boaters,

I am re-fitting a 39 year old Allied Mistress and the deck has extensive stress cracking, probably due in part to the hot Texas sun.

I would be genuinely interested in anybody's experience with the repair of the cracks. I will have her re-painted with epoxy. Will that be enough to fill those cracks permanently, or will they reappear?

Please name any products and/or procedures that you or the yard has used on this problem.

Thanks kindly, for any and all experiences and advice,
Mack Robertson
Allied Mistress Hull #7
S/V Island Mistress
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Old 08-05-2015, 15:01   #2
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Re: Repairing deck gellcoat stress cracks

Use a burr bit, or high speed cutter for your dremel tool and scarf out the cracks into a V.
Get below the crack, meaning you should have "smooth" gelcoat in the V, the crack no longer visible.
Vaccum the V, wipe with acetone,
brush the V full with gelcoat, let dry and wet sand smooth.
Hardest part is matching gelcoat color, but if you're re- painting later no worries.
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Old 10-05-2015, 12:55   #3
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Re: Repairing deck gellcoat stress cracks

Hello Mariner Bob,

Thanks for the reply. I have a lot of these stress cracks; some short and some quite long, even on inside and outside curved surfaces.

Since I have never owned a Dremel tool. I am wondering if it is hard to control like a router without a guide? The bit probably has much less power and surface bearing area?

Due to the cost of yard help, I will probably try doing this work myself as weather allows. These cracks don't leak, but need fixing before a deck re-paint.

I will try it out nevertheless. Thanks for the information. I'll let you know how it goes.

Best regards,
Mack
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Old 11-05-2015, 00:42   #4
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Re: Repairing deck gellcoat stress cracks

The cracks are caused by something. I would look for the cause 1st. If it gets painted, then I would vee it out like mariner36bob suggests, but just fill with a quality epoxy and sand it to match the contour. The straight epoxy bonds better than gel coat.
A dremil with the right bit can be held like a pen. You should be able to follow the crack. Besides, your going to paint over it. The wider the vee, the more area the epoxy has to bond to. Hopefully making a permanent repair.
If I was doing the repair in a shipyard, I would grind/sand the crack to an inch wide and down to the crack bottom to get a bigger bonding area. I would also look for proper deck supports in the vicinity of the cracks.
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Old 11-05-2015, 06:20   #5
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Re: Repairing deck gellcoat stress cracks

Well The boat is 39 years old this year and has spent most of its life in Florida and Texas. The construction of these vessel is legendary and rugged. So, I believe that it is due to the materials available in 1976 and the direct sun on the decks as well as stresses and strains incurred during use. I think your suggestion of epoxy is a good one.










I would welcome comment from other Allied Users with similar conditions.
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Old 11-05-2015, 06:44   #6
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Re: Repairing deck gellcoat stress cracks

I have a 35 year old Corbin, gel coat cracks on the deck almost from the beginnng due to gel coat too thick. I drilled holes at the end of the cracks to prevent further propogation which was successful but not had luck with cracks recurring. Try filling with smthng flexible like 5200 after veeing then paint over.
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Old 11-05-2015, 08:50   #7
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Re: Repairing deck gellcoat stress cracks

Negative on using 5200.

Negative on opening cracks up to 1" wide.

Yes on epoxy.

Overly thick gelcoat shrank from decades in FL sun.
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Old 11-05-2015, 09:14   #8
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Re: Repairing deck gellcoat stress cracks

There's lots of options our there.
http://www.magicezy.com/how-to-artic...uctural-level/

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Old 11-05-2015, 12:44   #9
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Re: Repairing deck gellcoat stress cracks

I am re-fitting a 39 year old Allied Mistress and the deck has extensive stress cracking, probably due in part to the hot Texas sun.

If you don't fix them correctly they will always come back! just filling with gelcoat does not fix the problem.



this video shows the correct way of fixing stress cracks.
and dont use 5200 on cracks...... that's just totally crazy!
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Old 11-05-2015, 18:33   #10
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Re: Repairing deck gellcoat stress cracks

Aside from the repair of places that need repairing, if you are going to paint anything I have had great success with Kiwi Grip. Thick enough to cover anything and durable. I had doubts before trying, but it has been a few years now and I am pleased.

I've done the patch of gelcoat mentioned here and found it either impossible or way too much trouble to match perfectly. Our eyes are incredible sensitive to the slightest color differences. If you really care about the look, you would repair the cause of the cracks, since it is likely structural, and then fix the gelcoat so it is flat, and then paint the decks with your choice of paint or non-slip where appropriate.

I can attest to it making a wonderful difference in the appearance of your boat.
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Old 11-05-2015, 19:36   #11
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Re: Repairing deck gellcoat stress cracks

Quote:
Originally Posted by mackrobertson View Post
Hello fellow boaters,

I am re-fitting a 39 year old Allied Mistress and the deck has extensive stress cracking, probably due in part to the hot Texas sun.

I would be genuinely interested in anybody's experience with the repair of the cracks. I will have her re-painted with epoxy. Will that be enough to fill those cracks permanently, or will they reappear?

Please name any products and/or procedures that you or the yard has used on this problem.

Thanks kindly, for any and all experiences and advice,
Mack Robertson
Allied Mistress Hull #7
S/V Island Mistress
Mack, they are not all stress cracks, you probably have lots of spider cracks like I had. I also have an Allied boat (Luders 33) and the gelcoat is very thick, so no matter what you do, they come back. I re-did all my cabin top. I opened the large cracks with a dremmel, filled with epoxy primed, over coated with Awlgrip, then put Kiwi Grip. That was 2 years ago and I can already see some tiny cracks forming again. If you are have lots of spider cracks just sand, prime and paint. This is just cosmetics.
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Old 11-05-2015, 20:00   #12
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Re: Repairing deck gellcoat stress cracks

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Originally Posted by SVTatia View Post
Mack, they are not all stress cracks, you probably have lots of spider cracks like I had. I also have an Allied boat (Luders 33) and the gelcoat is very thick, so no matter what you do, they come back. I re-did all my cabin top. I opened the large cracks with a dremmel, filled with epoxy primed, over coated with Awlgrip, then put Kiwi Grip. That was 2 years ago and I can already see some tiny cracks forming again. If you are have lots of spider cracks just sand, prime and paint. This is just cosmetics.


Not you! I thought I'd spent a bit of effort trying to convince folks to grind and glass stress fractures/spider cracks. It's the only way to get rid of them forever. It drives me crazy when people suggest a dremel and fill.
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Old 11-05-2015, 21:05   #13
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Re: Repairing deck gellcoat stress cracks

Thank You All for your insight and suggestions. I do know better than to paint over 5500, though that is the greatest caulk ever invented,that I know of, and I used PRC (invented by the genius at BF Goodrich) on the teak decks of my Herreshoff 28 many years ago.

I know that I have both spider cracks (from dropped winch handles, etc...) and stress cracks and the sheer effort of dremmeling them out would take months! And, after looking at the tools and the small sixe of the cracks, I am sure I would do more damage (before 5 o'clock) than the cracks present, since they don't leak.

I am planning to get the decks painted with an epoxy paint. I saw a nice unipoxy job (with a nice tan non-skid) on an Allied Princess on this forum that impressed me very much. I wonder if there isn't an ultra-low viscosity penetrating epoxy with which to prime the decks.

I won't live forever and if it lasts 20 years, I will be very happy. Otherwise I imagine it would have to be ground down to bare glass and I don't want to do that.

SV Tatia, I would like to hear more from you since you seem to have a logical, technical and practical mindset.

Keep the thread going. Brainstorming was conceived and perfected in the USA and no suggestion is too absurd to mention. Out of all of information comes the eventual solution.

Kindest regards,
Mack
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Old 11-05-2015, 22:17   #14
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Re: Repairing deck gellcoat stress cracks

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Originally Posted by scuba0_1 View Post
There's lots of options our there.
How to Repair Hairline Cracks in Fiberglass | MagicEzy

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Have you or anyone else here actually used this? If so, is it any good or just a good idea that doesn't really work?
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Old 11-05-2015, 22:19   #15
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Re: Repairing deck gellcoat stress cracks

min's right--true stress cracks should be sanded through the gelcoat and matted.
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