Cracks in gelcoat
Printed From: CorrectCraftFan.com
Category: General Correct Craft Discussion
Forum Name: General Discussion
Forum Discription: Anything Correct Craft
URL: http://www.CorrectCraftFan.com/forum/forum_posts.asp?TID=1413
Printed Date: April-16-2025 at 12:00pm
Topic: Cracks in gelcoat
Posted By: hyper1685
Subject: Cracks in gelcoat
Date Posted: April-05-2005 at 3:05pm
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I was waxing my 86 the other day and noticed some large cracks in the gel coat. There are 4 of them just below the stripe on the side of the boat. It is above where the fender is on the trailer. It seems like maybe the boat was put on the trailer sideways and was sitting on top of the finder and stressed it enough to crack. The cracks are a couple feet long and about an inch apart. How bad could the damage be? Is this something that needs immediate attention, or can I leave it for the summer (boat is already at the lake).
Thanks, Chris ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=651&sort=&pagenum=1&yrstart=1986&yrend=1990 - My Boat |
Replies:
Posted By: David F
Date Posted: April-05-2005 at 3:54pm
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Stress cracks are a common occurance and are not an indication of structural failure. What they do mean is that the fiberglass flexed more than the gelcoat is able to bend without cracking. Fiberglass composites can and do flex more than gelcoat (brittle) without any adverse effect on the composites strength or longevity. Most boat manufactures try to reinforce areas that are prone to flexing to prevent the gelcoat cracks from occuring. However, they cannot cover all possibilities without making the boat needlessly heavy.
So, do not worry about the cracks this year as no harm will be done. If you want to fix them, you must grind away the gelcoat down to the fiberglass composite and "paint" in new gelcoat, then sand down flush with the surrounding gelcoat then polish. Sand starting with 120, 220, 320, 400, 600, polish. Some people go past 600, but I find it unecessary. Make sure your sanding area grows with each successive grit of paper. A dremel tool is a good means of grinding out the crack. The groove or removed material does not need to be wide, just down to fiberglass (1/8" wide groove is plenty). If you just cover up the crack, it will reappear almost immediately. The hardest part of making an invisible patch is matching the gelcoat color. Color kits are available, but hard to get a good match. The easiest way is to order the gelcoat through a CC dealer for your particular boat and color scheme. The problem is that 1 gallon is the minimum order and a gallon of custom gelcoat color will cost you about $180.00 from a CC dealer. |
Posted By: kenny g
Date Posted: April-05-2005 at 8:25pm
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well , your 1/2 right david .if u "dremel" out the crack and fill it back in with GELCOAT you've just wasted your time.
wanna start a 40 page debate ? you said "if you just cover up the crack,it will reappear almost immediadiadely" how true! now you want to fill that crack with what? gelcoat? it is very clear someone has given you some bad advice.please do not pass this advice on to others.this can be a very expensive mistake. ------------- kenny g |
Posted By: Guests
Date Posted: April-05-2005 at 11:48pm
| Kenny, Can you be more specific on what to use? I have the same problem and would like to take care of it with-in the next 2 weeks before I put the boat in the dock. |
Posted By: fishtique 20
Date Posted: April-06-2005 at 1:32am
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well, is it realy stress cracks or crazing.
I can advise from first hand,after a 4 year restore its crazing. my 77 fish tique was in need of a lot of love.1/8 in grind fill w/chop and resin.  good to go.
paul c ------------- 20' Fish Tique 370hp http://photobucket.com/albums/y21/fishtique20/ - **PICS** Jacksonville, FL |
Posted By: David F
Date Posted: April-06-2005 at 1:49am
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Kenny:
If you do not believe me, that is fine. It is an acceptable practice and NOT my advice, but the advice found in many books covering fiberglass repair. I am in the process of repairing a severly damage boat and have done extensive research and purchased several books and videos on the subject. I trust the authors who have been repairing fiberglass boats for many years. I am just passing along what I have read and practiced, not what I dreamed up. I will clear up one thing. If the source of the stress is not corrected, then yes the cracks will reappear. If the stress was one unusual event, then no they will not reappear. I am curious why you think replacing gelcoat with gelcoat is a bad idea. Remember, I said grind through the gelcoat to the fiberglass. I did NOT say grind into the fiberglass and replace fiberglass/resin with gelcoat. Help me learn something new if you know I am wrong, just do not say I am wrong...why? |
Posted By: fishtique 20
Date Posted: April-06-2005 at 2:04am
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dont get defensive i am just basing results on personal facts. Stress or crazing is a composite crack it must be ground out to repair . ------------- 20' Fish Tique 370hp http://photobucket.com/albums/y21/fishtique20/ - **PICS** Jacksonville, FL |
Posted By: kenny g
Date Posted: April-06-2005 at 2:17am
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grind em out.! put glass back in.
a chopper gun job cost $$$ but u have a beautiful boat paul ! crazing/gelcoat cracks as david said are somewhat different from stress cracks,however the repair process is the same. paint the front door of your house every year for 20 years.what happens? the paint cracks! why ? it's too thick ! spray gelcoat too thick in a mold and after a while we have cracks in the finish.gelcoat was never designed to be a filler but a hard durable finish.fiberglass makes a much better filler. ------------- kenny g |
Posted By: David F
Date Posted: April-06-2005 at 2:18am
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Well, I agree that gelcoat cannot be used to repair a composite failure. But, stress cracks in gelcoat can and do occur without cracking of the fiberglass composite. Gelcoat is hard and brittle whereas fiberglass composite is somewhat plyable. Think of a fiberglass composite pole vaulting pole. Now think of what would happen if the pole was coated in gelcoat...the first time the pole was used, the gelcoat would crack and almost fall off. Yet, the fiberglass composite of the pole would be fine. Now, I am not trying to say the composite of our boats is akin to pole vaults, just a way of illustrating a point.
Again, repair fiberglass composite with fiberglass and resin (my choice of resin is epoxy regardless of original resin). Repair gelcoat with gelcoat. Oh and Kenny, sorry for the debate, I will try to keep it under 40 pages. And "fishtique 20", I am sure you know what you are talking about as your boat is a beauty. |
Posted By: David F
Date Posted: April-06-2005 at 2:28am
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Kenny:
I would love to send you a photo of one of my repairs and you will see I am qualified to make the comments I make. I am having to patch holes punched through the composite, replace the bow that was crushed. Replace the port side bow at the upper deck to hull seam due to being crushed. My method is to cut out crushed areas, grind away all delaminated composite material, lay up new composite of equal thickness as original on a 12:1 taper to original undamage material, fair out with epoxy resin mixed with a thickening a sanding "powder", spray gelcoat, sand, polish. If you look close, you can see the gelcoat blend line, but you have to look close. I will try to post a before and after picture, if I can figure out how. |
Posted By: hyper1685
Date Posted: April-06-2005 at 7:19pm
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Thanks for the help wveryone. could someone tell me what the difference between crazing and cracking is, and how to fix each type.
thanks, chris ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=651&sort=&pagenum=1&yrstart=1986&yrend=1990 - My Boat |
Posted By: 79nautique
Date Posted: April-06-2005 at 7:59pm
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Good question? there the same to me. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=756&sort=&pagenum=1&yrstart=1979&yrend=1979 - 79 nautique |
Posted By: David F
Date Posted: April-07-2005 at 2:49am
Here are a couple of during and after pictures of one of many repairs I am making to my '93 SN. I could not find the before on my home computer, but will add it later.
This is my first repair of a hole punched completely through the composit. The brown fairing compound is epoxy with a thickener eand sanding aid. The white below is white gelcoat that I used to fill pinholes in the new fiberglass work because I overbuilt and had to grind down a bit, thus fairing compound not really needed in this area. |
Posted By: kenny g
Date Posted: April-07-2005 at 1:48pm
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that repair looks good david,and i'm sure your bow repair will turn out just as well.
for someone who took the time to gather books,video's and fiberglass repair information thats great! however,i know from years of hands on experence making a living at it that gelcoat is not used as a filler in cracks regardless of what the auther of the book claims. ------------- kenny g |
Posted By: David F
Date Posted: April-07-2005 at 3:08pm
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Thank you for the compliment. Maybe we agree anyway. I look at it as not filling the crack, but rather removing the (gelcoat) crack entirely by grinding out a v-groove with a generous taper and then replacing gelcoat with gelcoat. I only do this on where there are isolated cracks. If there are many cracks in one area, I grind off ALL the gelcoat and spray on new to a tapered blend line.
You could be completely right and I end up being very sad after the first day the boat is back on the water. I will update the forum at that time. |
Posted By: David F
Date Posted: April-17-2005 at 11:32am
Here is what I started with...
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