Best method to repair stress cracks

Discussion in 'Fiberglass and Composite Boat Building' started by grady, Jul 24, 2007.

  1. grady
    Joined: Oct 2006
    Posts: 503
    Likes: 11, Points: 28, Legacy Rep: 70
    Location: Scituate, Ma

    grady Novice

    Hi everyone, I've been busy stripping my hull of all hardware, trim and upholstery. But now I am prepping for paint and I'm uncertain how to proceed in the mitigating of those tiny little stress cracks. I would think that you would want to open them up to be able to push some thicken epoxy into the area.

    But then I think about all that grinding, filling, fairing and priming, I wonder will a good med build primer fill these cracks? And if they do fill with primer will they reappear?

    ANY GUIDANCE IS APPRECIATED


    THANKS
     
  2. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 470, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    First determine if they are really stress cracks. If there is an underlying issue causing the area to flex excessively or some sort of laminate damage, then you'll be fixing the same area again.

    You could fill the opened cracks with a high build primer, but you'd be laying down a lot of paint for the average crack. I think this is asking a bit much from primer.

    Yep, grind it back to clean, stable material, fill and fair. Sorry . . .
     
  3. grady
    Joined: Oct 2006
    Posts: 503
    Likes: 11, Points: 28, Legacy Rep: 70
    Location: Scituate, Ma

    grady Novice

    Thanks Par, For the quick reply.

    Most of these are small, spider type cracks that seem to start in corners. They are all short in lenght and appear shallow in depth. Almost going unnoticed, except of course to me.

    One area shows much longer cracks on the gunwale above the rub rail. Approx 6-8" long, this area was hit by sail boat that miss his mooring. There was damage that was repaired close to this area.

    Hope to keep the grinding to a minimum, But what tool would you suggest to open up the cracks. I was thinking, maybe a dremel type presicion grinder. As most of these cracks are in tight spots,in or around corners where two or more surfaces come together.

    Thanks Again for all your help.


    Grady
     
  4. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 470, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    I usually don't screw around trying to be too neat about it and the edge of a disk grinder does the deed quickly. In tight spots a Dremel (I use a high speed pencil grinder) or Roto-Zip can work. I figure the area needs to be faired anyway, so why bother. If you'd like to be neater, then a Dremel can work, though I've often found this particular tool doesn't have the nuts to do much more then polish jewelry. Don't try to be too neat, the repair needs surface area to stay stuck, so open them up good. You can be neater with your filler applications, to save sanding time.
     
  5. grady
    Joined: Oct 2006
    Posts: 503
    Likes: 11, Points: 28, Legacy Rep: 70
    Location: Scituate, Ma

    grady Novice

    Thanks Par. Yeah I thought I would use the the 4" grinder on the open areas. But I'll have to figure out what tool will work in those tight corners.

    Anyway thanks again, And of course there are a couple of other issues, I have some small screw holes where snaps were attached. And I need to fill them. I was thinking about countersinking these holes and filling with an epoxy-cabo sil puddy, They don't seem big enough to warrant a glass patch.

    Please advise.

    Best Regards

    Grady
     

  6. the1much
    Joined: Jul 2007
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    Location: maine

    the1much hippie dreams

    start small

    by the sounds of it, the cracks may be just in your gel-coat, id start off with a DA and 80 grit,,sand off the gel-coat and see if the cracks are in the actual fiberglass
     
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