Jump to content


Fix crazing.

Hairline crack crasing fiberglass repair

  • Please log in to reply
17 replies to this topic

#1 cpt_757

cpt_757

    Member

  • Members
  • PipPipPipPipPip
  • 47 posts
  • Location:Marina Del Rey, CA
  • Interests:Singlehand sailing.

Posted 20 March 2017 - 02:06 PM

I was told to use Polyurethane adhesive/sealant(colored) to fix hairline crack / crazing on fiberglass surface. I believe it works but is it quite right way?
How do you fix crazing?

#2 cpt_757

cpt_757

    Member

  • Members
  • PipPipPipPipPip
  • 47 posts
  • Location:Marina Del Rey, CA
  • Interests:Singlehand sailing.

Posted 20 March 2017 - 02:16 PM

And gel coat crazing, use gel coat filler?

#3 shavdog

shavdog

    Member

  • Members
  • PipPipPipPipPip
  • 46 posts
  • Location:Minnesota
  • Interests:sailing, golf, investing

Posted 20 March 2017 - 03:28 PM

I had a cape dory 22 ....cape dory line was known for gelcoat crazing...it's difficult to get rid of....on my nonskid I would put on a fresh coat of interdeck and that would keep it covered up for a couple of yrs then redo....I believe it's more cosmetic than anything...it does keep coming back ....



#4 DDW

DDW

    Anarchist

  • Members
  • PipPipPipPipPipPipPip
  • 3,474 posts

Posted 20 March 2017 - 03:45 PM

1) sand the gelcoat off and repaint with PU.

2) stiffen the structure with extra laminate and re-gelcoat

 

Those are really the only ways to fix it permanently. The substrate is more flexible than the coating, so the coating is cracking. You need to make the coating more flexible or the substrate stiffer. 

 

I'm assuming this is happening in corners etc. If happening all over then it is probably just the gel coat getting old and shrinking off.



#5 cpt_757

cpt_757

    Member

  • Members
  • PipPipPipPipPip
  • 47 posts
  • Location:Marina Del Rey, CA
  • Interests:Singlehand sailing.

Posted 20 March 2017 - 03:55 PM

1) sand the gelcoat off and repaint with PU.
2) stiffen the structure with extra laminate and re-gelcoat
 
Those are really the only ways to fix it permanently. The substrate is more flexible than the coating, so the coating is cracking. You need to make the coating more flexible or the substrate stiffer. 
 
I'm assuming this is happening in corners etc. If happening all over then it is probably just the gel coat getting old and shrinking off.

Thank you,
How about the hairline over fiberglass? Is it good using same way, sanding surface and repainted over?

#6 Third Reef Grim

Third Reef Grim

    Anarchist

  • Members
  • PipPipPipPipPipPipPip
  • 1,333 posts

Posted 20 March 2017 - 10:31 PM

1) sand the gelcoat off and repaint with PU.
2) stiffen the structure with extra laminate and re-gelcoat
 
Those are really the only ways to fix it permanently. The substrate is more flexible than the coating, so the coating is cracking. You need to make the coating more flexible or the substrate stiffer. 
 
I'm assuming this is happening in corners etc. If happening all over then it is probably just the gel coat old and shrinking off.

+1. The problem with GRP hulls is the gelcoat is more brittle than the laminate beneath it? So when the hull flex's tue laminate can mobe cause its got a fibre structure to support it but the gelcoat is just coloured poyester resin with no structure and as such just cracks.

#7 Raz'r

Raz'r

    Anarchist

  • Members
  • PipPipPipPipPipPipPip
  • 32,099 posts
  • Location:San Francisco Bay
  • Interests:Rum

Posted 20 March 2017 - 11:11 PM

 

1) sand the gelcoat off and repaint with PU.
2) stiffen the structure with extra laminate and re-gelcoat
 
Those are really the only ways to fix it permanently. The substrate is more flexible than the coating, so the coating is cracking. You need to make the coating more flexible or the substrate stiffer. 
 
I'm assuming this is happening in corners etc. If happening all over then it is probably just the gel coat getting old and shrinking off.

Thank you,
How about the hairline over fiberglass? Is it good using same way, sanding surface and repainted over?

 

 

sanding surface yes, but all the way to glass.just roughing up the gel coat will transmit the cracks.



#8 DDW

DDW

    Anarchist

  • Members
  • PipPipPipPipPipPipPip
  • 3,474 posts

Posted 21 March 2017 - 01:21 AM

If gelcoat is spider crazing in areas that don't appear to flex much, it is probably just failing due to age. Gelcoat is brittle, and gets more brittle with age. I'm not sure if this is UV exposure or drying out, but I have seen many cases of a broad expanse of gelcoat, all spider crazed, with a small section in the middle covered in say vinyl lettering or a painted on name. Under the vinyl/paint it looks like new. If it is spider crazing, you can have success sanding it down until the crazing is removed, which may not be all the way to the laminate. Then repaint with PU, which sticks much better, is much more flexible, and stops the deterioration of the gel coat. If you go all the way to the laminate then there is significant expense/labor in repriming and refairing. 

 

It would be helpful to see a picture. 

 

If it is just a few cracks, the usual remedy is to reef them out wider (Dremel etc.), fill with gel coat patching stuff, sand smooth. You have to reef them wider or the patch will not stay stuck. It is usually very difficult to make this look good, because you are trying to match an old faded color with new unfaded color, which is going to fade at a different rate. But it might look better than the cracks for awhile. 



#9 cpt_757

cpt_757

    Member

  • Members
  • PipPipPipPipPip
  • 47 posts
  • Location:Marina Del Rey, CA
  • Interests:Singlehand sailing.

Posted 21 March 2017 - 04:58 AM

Pictures here.

Attached Files



#10 hobot

hobot

    Anarchist

  • Members
  • PipPipPipPipPipPipPip
  • 22,508 posts
  • Location:Riggers Hollow Archipelago, Wa. USA

Posted 21 March 2017 - 10:43 AM

The first pic looks like damage caused from flexing.

#11 cpt_757

cpt_757

    Member

  • Members
  • PipPipPipPipPip
  • 47 posts
  • Location:Marina Del Rey, CA
  • Interests:Singlehand sailing.

Posted 21 March 2017 - 02:44 PM

The first pic looks like damage caused from flexing.


Yes, i am thinking same,,

#12 DDW

DDW

    Anarchist

  • Members
  • PipPipPipPipPipPipPip
  • 3,474 posts

Posted 21 March 2017 - 04:13 PM

I think the first pic looks like scratches, not cracking. Someone ran into your boat. Scratches will have a V shaped cross section while cracks should be tight (until pieces fall out). Look very closely at it, with an eye loupe if possible. If someone hit it, there may also be stress cracking in the area. 

 

The second one looks like the gel coat is shrinking off the surface. Maybe it was applied extra thick there. In that area, you could sand down and paint or re-gel coat. 



#13 Will 1073

Will 1073

    Anarchist

  • Members
  • PipPipPipPipPipPipPip
  • 328 posts

Posted 21 March 2017 - 05:43 PM

Lightly tap the crazing area in the second picture. My money is that there's a void between the gel coat and glass in the area. A rather sharp corner like that it's pretty common that the guys laying up the hull didn't manage to get the glass into the bend.

That or DDW's theory of too thick gel coat application that has shrank.

#14 hobot

hobot

    Anarchist

  • Members
  • PipPipPipPipPipPipPip
  • 22,508 posts
  • Location:Riggers Hollow Archipelago, Wa. USA

Posted 21 March 2017 - 09:40 PM

The first picture, where is that on the hull, at the bottom of the transom? If it is I'd think the cracks are right along the inside taped edge of the hull and deck are bonded together. Some additional reinforcement should be layed up inside as part of the repair.

The second picture, could very well be from thick gel coat.
Remember you're looking at it from upside down as to how the part was made. That that toe rail was a trough on the mold, very easy to overspray that area when applying the gel coat.
Overall an easy gelcoat repair.

#15 cpt_757

cpt_757

    Member

  • Members
  • PipPipPipPipPip
  • 47 posts
  • Location:Marina Del Rey, CA
  • Interests:Singlehand sailing.

Posted 22 March 2017 - 04:39 AM

The first picture, those cracks came up sudden, like an over night. I did not have any idea what's happened.
I understood now for the second picture.
Thank you, all!

#16 duncan (the other one)

duncan (the other one)

    Anarchist

  • Members
  • PipPipPipPipPipPipPip
  • 3,725 posts
  • Location:Siderney

Posted 22 March 2017 - 10:06 AM

Is that first pic your stern overhang?

 

Is it possible someone - or something, like a floating dock - got under there and the boat slammed down on it?

 

Have a look at the hull underneath and see if there's any evidence of something hitting it.



#17 cpt_757

cpt_757

    Member

  • Members
  • PipPipPipPipPip
  • 47 posts
  • Location:Marina Del Rey, CA
  • Interests:Singlehand sailing.

Posted 22 March 2017 - 01:57 PM

Is that first pic your stern overhang?
 
Is it possible someone - or something, like a floating dock - got under there and the boat slammed down on it?
 
Have a look at the hull underneath and see if there's any evidence of something hitting it.

Thanks, I started thinking that way, will check out.

#18 BobBill

BobBill

    Anarchist

  • Members
  • PipPipPipPipPipPipPip
  • 3,040 posts
  • Location:Wakes in "Gingerville," SE Minnesota.
  • Interests:Odd "?" but name it!

Posted 22 March 2017 - 02:59 PM

I had a cape dory 22 ....cape dory line was known for gelcoat crazing...it's difficult to get rid of....on my nonskid I would put on a fresh coat of interdeck and that would keep it covered up for a couple of yrs then redo....I believe it's more cosmetic than anything...it does keep coming back ....

+1. Still, there are ways to fill, wipe and let cure using epoxy. Depends. comment 12 and 13 seem logical also. I did not own the boat, but acquaintance did and I crew when racing. He was constantly fiddling with finish, especially inside the cuddy, which I would have done up every couple years, as it appeared.







Also tagged with one or more of these keywords: Hairline crack, crasing, fiberglass repair

1 user(s) are reading this topic

0 members, 1 guests, 0 anonymous users