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Old 01-22-2019, 08:12 AM   #1
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Gelcoat Cracks - Do they wet the core?

While I am getting a fair amount of the deck's wet coring replaced that entered around deck fittings (factory issue), my fiberglass guy is looking at a lot of gelcoat cracks and saying that even small cracks allow water into the core. Is this a correct claim? I know fiberglass is porous, but does any water under the gelcoat find its way to the core at a volume that would need addressing?



I have pretty much opted to not keep him on to chase deck cracks. I have heard it is a heck of a rabbit hole. He kinda priced himself out of the job, but I was considering learning how to do some of the bigger ones myself (to date, I have been pretty poor at fiberglass work, but I want to learn)


Is it really something we should move up the to-do list?


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Old 01-22-2019, 09:03 AM   #2
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I guess the answer is relative to the thickness of the fiberglass underneath and whether it's also cracked. Fixed a number of cracks during the refit with out any water intrusion issues. I would likely be more concerned if water pooled over a cracked area.

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Old 01-22-2019, 09:03 AM   #3
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Gel coat is considerably harder and more brittle than the underlying fiberglass resin base, so it cracks sometimes because the underlying fiberglass flexes but the gel is too brittle. I believe that in most cases gel coat cracks are cosmetic and don't affect the underlying fiberglass or core. I would fill the bad ones, but as you imply they often come back.


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Old 01-22-2019, 09:42 AM   #4
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I don't know if the cracks would be an issue.... depends. Seems like if the fiberglass coating underneath was done well, no problem.

However, I've got cracks, too. The way I fix them is sand down and put a layer of flexible epoxy on underneath, sand down and put the gel coat over it. If it cracks again (which hasn't happened unless I hit something), it would unlike allow water into the hull.
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Old 01-22-2019, 09:52 AM   #5
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Moisture test cracked areas. If moisture is excessive then you probably have leakage. Drill exploratory small holes to estimate extent of problem from moisture on drill debris. Consider pumping resin through holes and resealing holes and cracks. If just cosmetic, try to fill with color matched resin.
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Old 01-22-2019, 10:10 AM   #6
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Quote:
Originally Posted by djmarchand View Post
I believe that in most cases gel coat cracks are cosmetic and don't affect the underlying fiberglass or core. I would fill the bad ones, but as you imply they often come back.
I had numerous gel coat cracks that I had professionally fixed and a few did come back but no water ingress was found.

Keep in mind that a boat is designed to live in a Richter Scale 10 environment on a daily basis. You will always have some hull and topside movement.
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Old 01-22-2019, 11:23 AM   #7
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Here is a link to a YouTube channel that has a lot of fiberglass repair information: http://://www.youtube.com/channel/UC...zdqFUk3oTaHBuA

Well that didn't work. Try Boatworks Today.com
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Old 01-22-2019, 11:30 AM   #8
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It can be as simple as the gel coat being applied too thickly. We had a bunch of stress cracking and it was due to way too thick gel coat. I did not find any that penetrated the fiberglass. In one area I took my belt sander with 36 grit and completely removed the gel coat. Rebuilt the surface and then painted the boat. The only way to really find out it to grind it away until you hit solid glass. I could see a white crack in the glass where any crack was deep. Ground down til the white crack was gone. If it was too deep then I laid new glass and faired it out. If it was not deep then just faired it out and painted.
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Old 01-22-2019, 12:52 PM   #9
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A belt sander is a little aggressive for stress cracks. I would use a Dremel with a small cutting bit to widen the crack a bit so it will take a filler or some chopped fiberglass and resin.
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Old 01-22-2019, 01:10 PM   #10
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When I bought my 1977 42' Californian, it had been neglected for many years. There was significant, deep gelcoat crazing in many places including some areas of the deck. The hull was all fiberglass, but the deck and house were glass over plywood.


It was a lot of work to grind through all of the crazed gelcoat to get down to the good gelcoat or, in many cases, the fiberglass itself. From there it had to be built back up with primer before AwlGripping.

But, except where the fiberglass was compromised by something else, there was no problem at all with the glass or the plywood underneath -- even in the worst areas. And, we did take all of the gel off to get to the fiberglass in many cases, so we would have known, even if it wasn't otherwise easy to find by sounding.

On the mid-deck, there was some delamination between the fiberglass and the plywood as a result of water intrusion. But, this came from penetrations on the mid-deck. I think they were associated with the old dinghy rack and other deck gear.


In general, epoxy and other similar resins don't really react well to UV light. So, I guess light could weaken it over time, eventually leading to failure. But, in practice, I suspect enough dirt and grime make their way into the crazing to protect it. And, a lot of deep crazing doesn't go all the way to the glass.




Quote:
Originally Posted by Tom.B View Post
While I am getting a fair amount of the deck's wet coring replaced that entered around deck fittings (factory issue), my fiberglass guy is looking at a lot of gelcoat cracks and saying that even small cracks allow water into the core. Is this a correct claim? I know fiberglass is porous, but does any water under the gelcoat find its way to the core at a volume that would need addressing?



I have pretty much opted to not keep him on to chase deck cracks. I have heard it is a heck of a rabbit hole. He kinda priced himself out of the job, but I was considering learning how to do some of the bigger ones myself (to date, I have been pretty poor at fiberglass work, but I want to learn)


Is it really something we should move up the to-do list?


Thanks-
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Old 01-22-2019, 01:26 PM   #11
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Thanks everyone. That is kinda what I figured. I may attack some of the bigger ones and prime/paint over the smaller ones. One thing is for sure it's that the fiberglass layer Navigator built up on the decks is very sturdy. We had VERY wet core around the engine room hatch hinge, around the cockpit drains, around the fuel fill fittings (also in the cockpit), and around the chain hole under the windlass. However, there was no flex at all from the fiberglass above it. In fact, if we didn't go looking for it because we knew it existed, we would not have known it was there from walking on it. I just wish they had sealed the core around the holes they drilled for all the hardware. Seems silly that they didn't. Thanks again...
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Old 01-22-2019, 01:57 PM   #12
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I used the belt sander in an area that was a complete spider web of stress cracks. Way too thick gel coat. I just took off all the gel coat because it would have just kept cracking. In areas that had a bit of stress cracking, I chased the cracks with a dremel and then filled them. Where the cracks went into the fiberglass I used a right angle drill with a 36 grit rol-loc disc and ground down to solid fiberglass. Then added glass back and faired it out. Then I painted the whole boat. The painter who shot the boat told me he would have charged $25k to do all the work. As it was I paid him $900 to shoot the whole boat after I had it prepped. Keep in mind our area is fairly economical to have this work done. The hard part isn’t repairing the cracks, it is the finish you put on top of the repairs that is difficult, getting gel coat to match and look good is the tough part to me.
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Old 01-22-2019, 02:43 PM   #13
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I wonder if the "overlapping platelet" technology of Interlux 2000 barrier coat would provide a semi-flexible skin over small spider web stress cracks? I'm thinking of using it on the fiberglass fenders on my old pickup with that aim. Another automotive product which I believe might have some promise is Raptor bed liner. It's a fairly low viscosity spray-on flexible polyurethane.... sands easily and can be overcoated with urethane paints like Interlux Perfection among others. Their tech line folks think it would work to fill the tiny cracks and act as a tough membrane-like substrate.
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Old 01-22-2019, 03:44 PM   #14
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I doubt that Interprotect 2000 would cover the stress cracks well, but maybe. Kiwigrip will cover stress cracks. I used it on my decks. Worked well and easy to repair if need be. I had to reglass a repair I did on the swim platform and the akiwigrip was simple to blend into the existing Kiwigrip.
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Old 01-23-2019, 08:00 AM   #15
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"so it cracks sometimes because the underlying fiberglass flexes but the gel is too brittle."

The gel frequently cracks when the underlying glass has cracked from overload.

Stanchion bases , stair steps where ever the load is too high for the layup.

Sadly the underlying laminate most be made stronger , which is messy and difficult.
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Old 01-23-2019, 10:12 PM   #16
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Some old timer once schooled me to try a can opener. I’ll be damned if you get a sharp one if it doesn’t open up the seam with a perfectly scarfed angle and all. Fill just shy of the surface, then sand the surface 4-6 inches with around 100 grit, get all the shine off. Then finish with a blended spray of gel, wet sand and then buff. Not rocket science, but takes patience. If you simply fill and sand flat, you will Always see the repair stand out. Spray blend and if the color is close, you will never see it.

I’ve never had a stress crack that went beyond the gel unless the underlying layer was compromised long before the gel ever cracked.
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Old 01-23-2019, 10:45 PM   #17
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Gelcoat fractues may be just cosmetic surface crazing and as long as the underlying laminate is sound, pose no threat to the core. Moisture meters tell lies but in this case I believe they would be fairly reliable. You do not need a $300 or $700 moisture meter, in fact I have not taken those out of my bag since I found the $40 Ryobi unit from Home Delpot which is now my favourite by far. I'd suggest you read Moisture Meter Mythology then invest $40 at Home Depot.

PS. The photo of the Ryobi unit is at the very bottom of that article.
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Old 01-24-2019, 07:20 AM   #18
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I use Raptor in car restorations. It will discolor when exposed to uv, so it must be overcoated. Even when dyed or tinted, it discolors. Great product though. I always use it black. Would be a great bilge finish. Very similar to Imron or Awlgrip in hardness.
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Old 01-28-2019, 01:58 PM   #19
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The issue is more important if the boat will be in a freezing area. The risk is that even small cracks will grow from the freeze thaw cycle creating an accelerating progressive potentially serious problem.
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Old 01-28-2019, 02:01 PM   #20
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Boat Works Today (I think) has some videos on how to repair them.
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