Possible signs of Osmosis?

Discussion in 'Fiberglass and Composite Boat Building' started by Jonny3777, Sep 26, 2017.

  1. Jonny3777
    Joined: Sep 2017
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    Jonny3777 Junior Member

    Hi all, I recently bought this boat she's 27ft not sure about model or age. The previous owner bought it to restore but had no time to finish it. I bought it as an ongoing project on a budget On first inspection all looked well was stored in a dry shed for over a year while he worked on it had been out of the water for a long time. I started reading about this thing called osmosis on boats but unsure about my boat. As you can see in the picture the little blisters are only about 1mm in diameter but they are all over the topside of the hull. when I pop them with my fingernail they have such a minute amount of moisture in them, so I can't tell if they smell like the vinegar odor I read about. The anti-foul will need re-coating I'm sure as it's very flaky. I'm totally new to boats as this is my first one. Hoping you guys can shed some light on this, I'm hoping this isn't a huge problem because as I said I'm on budget and wouldn't be able to afford the hire of a professional, Hoping I can solve this myself. I plan to use it in fresh water and I know that is worse for osmosis but I want it for river and lake cruising. Thanks
     

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  2. Ike
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    Ike Senior Member

    some references Hull Blisters on Boats and Yachts - by David Pascoe, Marine Surveyor http://www.yachtsurvey.com/blisters.htm
    http://boatsafe.com/nauticalknowhow/1220983tip.html
    Fiberglass Blister Repair by Don Casey - BoatTECH - BoatUS http://www.boatus.com/boattech/casey/blister-repair.asp

    If it is blistering it is very minor and can be fairly easy to repair. But it is odd to have it on a deck. It usually shows up on surfaces that are always wet. Actually cold fresh water is less likely to promote blistering. The worst cases are in warm salt water.
     
  3. ondarvr
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    ondarvr Senior Member

    It's very difficult to tell from the pics, but it looks like it's been painted and the paint is blistering.
     
  4. Nick.K
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    Nick.K Senior Member

    It looks like that to me too. Iv'e seen it happen many times. The blisters may come and go. I'm not sure exactly what causes it but probably it's some hygroscopic residue that wasn't removed from the hull surface before painting.

    If you discover blisters in the gelcoat under the water line, these will be 'osmosis'. Blisters also can and do occur over the water line where water is trapped against surfaces. Wet mats left long term on the cockpit floor are a typical culprit or moss on abandoned boats.

    Since your boat has probably been out of the water for a long time the hull may have dried out. It would be a good time to epoxy the under water areas.
     
  5. Jonny3777
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    Jonny3777 Junior Member

    Hi guys Thanks for the replies, I did think it was odd to have them so high on the hull and they do appear to be all over the hull. Would paint blisters still have moisture trapped inside them like mine do? I will sand them down and clean them out before I epoxy them.
     
  6. Nick.K
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    Nick.K Senior Member

    No need to epoxy over the waterline. The paint blisters are harmless and they'll probably disappear on sunny days anyhow. If you really want to get rid of them, try peeling off the paint with a sharp chisel instead of sanding; often the paint will peel off easily, it is faster and much cleaner. You will have to keep the chisel sharp, try a fine grade diamond 'stone' such as the one by Faithfull tools which is widely sold in Ireland.
     
  7. PAR
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    PAR Yacht Designer/Builder

    Likely just some outgassing, because the paint was applied, before the primer was actually fully cured. Sand, hit spots with glazing putty and repaint.
     
  8. Nick.K
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    Nick.K Senior Member


    OP's blisters are liquid filled, not gas filled. Sanding and filling is not a fix, they'll just pop up again somewhere else after the next days of heavy dew.
    Only solution is to strip the paint, wash the under surface and re-paint or decide to ignore it.
     
  9. PAR
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    PAR Yacht Designer/Builder

    Outgassing can cause the underside of the topcoat to become something other than what it once was, given some time and appropriate environmental condisions. The same is true with traditional blisters, though the process is a little different. Additionally, it could be simply poor surface prep during the layup or possibly a re-gelcoating with poor prep. Any experienced laminator should have little difficulty figuring out what these might be, assuming it's in the gelcoat. The same would be true of a paint job. Which is it, paint or gelcoat would be my first question.

    I suspect it's paint and poor surface prep is the problem. It looks like it needs a new paint job anyway, so . . .
     
  10. Nick.K
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    Nick.K Senior Member

    I once had this problem when doing joinery. I had made and fitted doors and windows which we had finish painted (airless spray micro porous). Shortly after I had a call 'Nick, you won't believe this but I have a funny problem, all your windows have little bubbles on the outside' My heart sank and I went out to have a look. Sure enough there were blisters all over with a brown liquid inside. I told her that would be nothing for it but to arrange for a painter to redo the outside. Some days later I called to arrange the date and she said 'you won't believe this, but the bubbles have gone...' and they never came back.
     
  11. Jonny3777
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    Jonny3777 Junior Member

    Thanks Nick, You really put my mind at ease, I'll do what you recommended and remove the paint. If its not a serious issue I'll leave it till the boat is finished inside and the cabin is rebuilt. Thanks gain
     
  12. Ike
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    Ike Senior Member

    Many years ago I helped a friend paint his six meter sailboat. I painted the deck. Within a few short days it blistered. As was said above, with very little effort the paint just peeled off. We had to completely re-prep and re-paint. The second try worked. What caused the first. Don't know.
     
  13. fallguy
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    fallguy Senior Member

    Sounds like uncured primer is a big issue. Thanks for the post.
     

  14. PAR
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    PAR Yacht Designer/Builder

    I'd simply hit it with a DA and some 80 grit (initially) to bulk remove the top coat, just to see what's really going on, of course in an out of the way test location. Next, I'd do a "peel" test on the primer and/or previous under coats. If the previous coats are well stuck, continue with bulk removal of the top coat and repaint. If the peel test showed signs of lifting, I'd continue grinding down until I could insure subsequent coatings (paint) will stick.
     
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