Delamination repair vs. gel coat repair

Thread starter #1
Sunfish repair questions...
It is my understanding that if I have circular patterns of spider cracking, then that means the hull took some blunt force and was delaminated. Delamination would mean sanding out the bad fiberglass and replacing that and repainting. If I have spider cracks that are just linear running bow-stern direction, then that would be a gel coat repair. Right?
Can delaminations show just the linear spider cracks? Or are they usually indicated by circular cracking?

Thanks.

Alex
 

mixmkr

Active Member
#3
You may already know this...but delamination is where adjoining fiberglass layers are separated from each other via several different causes...ie. poor fiberglass layup to impact forces, to water migration thru the gelcoat and reacting with the resin (blistering eventually leading to delamination). Spider cracking is typically limited to the gelcoat only, but not always and can go into the underlying fiberglass..... Caused usually by flexing, impact or other similar ways that would stress the thinner, gelcoat layer to finally crack. Commonly seen on areas of higher stress or impact areas. Gelcoat typically has no strength and is basically more a cosmetic feature and also aids in preventing water migration into the fiberglass.
So.... your original question would answer with no, no and no with your initial statements kinda missing the mark.
 

Webfoot1

Active Member
#4
There is only one layer of fiberglass on a Sunfish so no delamination but it is a valid question. You can
and probably will have plenty of spider cracks with no damage to the fiberglass. The only
way to determine if the fiberglass is cracked is to remove the damaged gelcoat. Post a picture
and we will probably tell you not to worry about the fiberglass and maybe not even worry about
the Spider cracking. As as Mixmkr mentioned a impact that damages the fiberglass may leave a
depression.
 

L&VW

Well-Known Member
#5
Sunfish repair questions...
It is my understanding that if I have circular patterns of spider cracking, then that means the hull took some blunt force and was delaminated. Delamination would mean sanding out the bad fiberglass and replacing that and repainting. If I have spider cracks that are just linear running bow-stern direction, then that would be a gel coat repair. Right?
Can delaminations show just the linear spider cracks? Or are they usually indicated by circular cracking?

Thanks.

Alex
My poor ex-racer-Sunfish has all kinds of gelcoat cracks. :( In some, I can demonstrate underlying structural weakness, in other cracks, not so much. :confused:

Recommendations everywhere in this forum is to "avoid paint". Elsewhere here, "gelcoat repair is difficult". :rolleyes: I've been letting the spider cracks "go" until a split in the gelcoat appears where it counts. (Like right where I am normally seated). :mad:

Here's a typical spider-crack, which I sanded—used automotive body filler on—and sprayed it with paint. (But was unable to totally erase it).

.

P5170005.JPG
 

Webfoot1

Active Member
#6
To fix gel coat cracks you need to open up the crack into a "v" slot then
fill with Marine-Tex. Lots of wet sanding involved. Unless it's a brand
new Sunfish or you want to practice you might want to use the time
sailing instead of fixing. My O.C.D. makes me want to fix every crack
but I was not granted a infinite lifetime so I mostly try to tell myself
the cracks are just in my imagination.
 

Webfoot1

Active Member
#8
You can fill the crack with ether one. If you got a expensive boat and want a invisible
repair you can color match gel-coat. You can fill with filler and spray a color match.
Marine-Tex is a bunch easier and quicker. You will not get a totally color matched
invisible repair but most Sunfish repairs don't get back to factory finish conditions.
Personally I learned from model airplanes in my youth that as soon as you get some
dings and repairs you stop worrying about future damage and start having fun. I
did try once to gelcoat a hull. I read all the instructions, unfortunately the one instruction
few talk about and I could not find is that gelcoat only has a shelf life of about a year.
Buying it from West Marine was the straw that broke the camels back.
 

L&VW

Well-Known Member
#9
This is the unsuccessful attempt to fill that spider-crack (above) with automotive body filler—before sanding smooth. :( Marine-Tex is said to require "hard sanding", which automotive body filler does not.

(The filler has worked—and has endured—everywhere else on the hull). :cool: I don't have the patience to go back and enlarge every one of those lines into a "V". Under a second "stress event", would it open up again? :confused:

P5170004.JPG
I should add that your "linear cracks" can be demonstrated to be due to structural weakness in the one layer of fiberglass roving underneath. Again, I'm not going to fix them until there's a "catastrophic event"—and then, I'd sand the surface down to dark fiberglass, lay down two layers of 4-inch tape, and leave the last coating of resin off. (For a textured surface, as I suggested earlier for a cockpit bottom repair).

.
 

signal charlie

Well-Known Member
Staff member
#10
Go sailing, enjoy the fact that the boat already has a ding :)

The circular pattern is a result of a point impact, the gelcoat and fiberglass flexed but returned to normal shape, no delamination, just gelcoat cracks. We have been using fairing compound lately to fill and sand, on really rough boats that we are painting. On our own boats we mostly ignore them. If the rest of the gelcoat is pristine and you are concerned with appearance I'd suggest learning how to use a gelcoat kit.

If the gelcoat starts to flake away then further investigation is needed, and some type of repair, either gelcoat, or epoxy putty like Marine Tex, or fairing compound and spot paint. The Manufacturer's repair would be to gelcoat.
 

mixmkr

Active Member
#11
Gelcoat has no strength and using it without a base filler will only crack immediately again. Quick, invisible gelcoat repairs aren't rocket science, but the unskilled repair always looks pretty ugly.....hence go sailing and enjoy the boat. A couple waves spilling over the bow makes them harder to see.
 
Thread starter #12
Thanks for the advise/info. I didn't know sunfish only had one layer of fiberglass. I have been known to over-think things... Do spider cracks let in a lot of water? I guess my main concern is the boat gaining weight.
 

Webfoot1

Active Member
#13
If it were a boat that was moored in the water for a extended length of time
then you may get seepage and water blisters between the fiberglass and gel coat.
For a Sunfish not really. Weight gain is through leaks in the hull seams, fittings and
dagger board barring any major damage. Pressure test a old Sunfish and you'll
find leaks aplenty. For the first name in water blisters, do a search for Pierson Yachts.
 

Webfoot1

Active Member
#15
Actually a fairly useless but true answer is that water will permeate
through any material given enough time. Sometimes a very
long time.
 

L&VW

Well-Known Member
#16
I should add that your "linear cracks" can be demonstrated to be due to structural weakness in the one layer of fiberglass roving underneath. Again, I'm not going to fix them until there's a "catastrophic event"—and then, I'd sand the surface down to dark fiberglass, lay down two layers of 4-inch tape, and leave the last coating of resin off. (For a textured surface, as I suggested earlier for a cockpit bottom repair).
Now I'm thinking the repair can go underneath the linear cracks of the usual cockpit seating area.

You'll notice the heavy pattern in the [non-gel-coated] fiberglass roving might limit the amount of strength in that repair. (It'd also be a more difficult repair, although I haven't tried it).

Not to risk a fracture of a possible repair-piece for Sunfish, here's a "quiet" demonstration of how well gelcoat adheres to a section of fiberglass roving, 5"x14"—without fracturing:

P8110032.JPG
 

L&VW

Well-Known Member
#17
To fix gel coat cracks you need to open up the crack into a "v" slot then fill with Marine-Tex. Lots of wet sanding involved. Unless it's a brand new Sunfish or you want to practice you might want to use the time sailing instead of fixing. My O.C.D. makes me want to fix every crack
but I was not granted a infinite lifetime so I mostly try to tell myself the cracks are just in my imagination.
Hurricane Irma knocked a hole in a corner of a Sunfish transom. The oval hole is 1" x ½". There is some existing firm backing..

Would you use Marine-Tex to fill and fix it?

.
 
Last edited:

L&VW

Well-Known Member
#19
Well, nobody in this rural area has Marine-Tex. :mad: It's a two-hour drive round-trip to West Marine. :rolleyes:

Now, not far from my "corner" repair was another "ding". But it showed that the hull was not originally red in color. :( This was to be my Hurricane Irma "rescue" (or "totaled"). I'm not so sure if I want to save it. :oops: Is this a Bondo special? (Before they became respectable for marine use).

fullsc36[1].jpg
 

signal charlie

Well-Known Member
Staff member
#20
Jamestown Distributors is a good source for Marine Tex, THIXO, Pettit, Interlux, RustOleum etc. Our local ACE carries Marine Tex but probably because we live on the coast.

I've never seen a Bondo Special but I'd guess that's what it looks like. I'd feather file/sand that area until you see good gelcoat. Marine tex is a quick approach, another is to wet out the area with neat epoxy to soak in and then thickened epoxy (THIXO or FLEXPOXY), leaving a very small depression. Then fair, sand and spot paint.

FMI: Jamestown Distributors

Back to work on the pirate ship...

IMG_7281.JPG
 
Top