Small fatigue cracks

[brainiac]

Hello all,

I am a new boat owner of an old 78 Mac Gregor. I'm looking into my project list, to spruce the boat up a little.

I've never done any fiberglass work before. There are a bunch of cracks here and there, at the main stress points. A particularly bad one is right at the door of the cabin. They are hairline cracks at the surface.

What is the best way to fix them?

Cheers!

[Diva27]

I won't bother addressing the many issues of what caused them. That's worth learning more about, especially if the situation suggests they may be recurring due to stresses that need addressing, in which case they're not going to go away with a cosmetic treatment. In brief, they're often due to shrinkage of the gelcoat over time, and smarter people can tell you about how the thickness of gelcoat in the mold can cause this. Starburst cracks usually are due to an impact on the inside of the fibreglass or a stress point. But anyway. A number of years ago I had a 24-foot one-design keelboat, a Shark, built in 1974 that had some cracks, some in the topsides. A member who knew a thing or two about glasswork recommended I get some Interprotect 2000 and apply TINY amounts along the cracks. The microplates infiltrate and fill the cracks, and then you wetsand away the small excess. I followed his advice and found it very effective. One warning is that if dirt has accumulated deep in the crack, the Interprotect will wick it to the surface and you may end up with a discoloured scar, so try to clean the treated area first.
Good luck!

[brainiac]

I have pictures, but I guess I am too new to be able to upload them here. Thanks for the info.

[Diva27]

If the cracks are real hairline you may have trouble forcing any Interprotect into them. If you really want to fill the fine ones you'll have to open them up with a Dremel. Otherwise consider the six-foot rule of a DIY paint job. If it looks good from six feet away, you done good. Grazing cracks should be treated the same way. If you can't really see them from a few feet away, I don't know if they're worth worrying about above the waterline, especially on deck and in the cockpit. Unless they point to a structural stress problem, they're largely cosmetic.
As I recall, I used a small foam brush to dab on the Interprotect. It's a very simple job and you're not risking any damage or misadventure, in my mind. Buy a small can and experiment.
cheers

[scottyt]

for small cracks, you should open then up even a little will help. a simple dental pick will open them enough to be better than nothing.

if the cracks are radiating out from some thing you can get to the back of, adding some glass would not be a bad idea. just dont go slapping on a lot of glass it can make the surrounding glass crack worse. first do a larger patch say 3 inches past all the cracking, then a smaller patch the size of the cracking. this will spread out the flexing over a larger area with out concentrating it all at the edges of the repair. use a lighter weight glass, not a build your boat heavy as heck glass. also make sure you prep any where you put the glass