Car bog on epoxy

Discussion in 'Fiberglass and Composite Boat Building' started by niczilla@mac.co, Dec 30, 2013.

  1. niczilla@mac.co
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    niczilla@mac.co Junior Member

    Hi all!
    We have been doing a MAJOR re fit on our Simpson 40 catamaran and have just spent the last year fairing the decks, at the start we had a painter slash supposed boat builder working with us and he was showing us how to fair the boat. To do this he was using car bog (goldrush) as it went off fast and was good to sand. Now thou we are pretty well finished and had someone come and say that the car bog will crack so as you can imagine we are a bit panicky...

    Does anyone have experience with a situation like this? The boat is a ply with epoxy glass over the top construction. We are considering laying a surface tissue with epoxy over the whole lot and faring that back with q cells to enclose the bog... We are open to suggestions!!!

    Thanks
    Nic
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    You certainly wouldn't expect polyester to bond well in this situation, but I'd be inclined to see what develops, seeing it is a cosmetic issue more than anything else. If there is flex, it may well let go more quickly than otherwise. You are thinking of epoxy over what, an unpainted surface, or a painted one ? If it is all painted and done, I'd give it a chance, you may be lucky and get away with it, at least for a time.
     
  3. michael pierzga
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    michael pierzga Senior Member

    Your fair a boat with epoxy bog....car bog is handy because it cures fast and is used only for small pin hole size imperfections.

    Dont fair your boat with car bog....and no car bog below waterline.
     
  4. PAR
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    PAR Yacht Designer/Builder

    Welcome to the forum.

    Yep, polyester bog over epoxy doesn't stick very well. You can try to lock it down with light fabric and epoxy, but it'll probably just delaminate off the surface of the underlying epoxy anyway. Vibration and flex is what will do in the polyester bond. Even if skinned over with epoxy and some sort of fabric, eventually you'll just have two skins, one attached to the plywood and the other floating under the outer skin. Of course, this will eventually break through or gather in lumps down by the boat's centerline. It'll probably look like a serious cellulite problem, from a distance.

    If you've done a major refit, short sheeting the fairing, just doesn't seem a reasonable economy. Yeah, I know this isn't what you wanted to hear, but it is reality. You have three choices - do nothing and hope for the best - try to skin it and hope for the best - or (yep it sucks) grind off the bog and fair again with epoxy. Sorry.
     
  5. Saqa
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    Saqa Senior Member

    I thought the way to use car quick fairing compound was to apply it over the primer and not straight on the base material. Does primer stick to 60grit rubbed epoxy? The car fairing stuff certainly sticks to the primer and is flexible too in thin layer applications. I am talking about the one part purple stuff that feathers like car paint when wet sanded with 360. The next step is to apply primer over the now smooth surface and paint sanding in between with 360
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    It sounds like the bog has gone straight on the epxy/glass, unless we learn otherwise.
     
  7. niczilla@mac.co
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    niczilla@mac.co Junior Member

    Ohh crap. That's what I thought, now I'm soo annoyed at not listening to everything I knew about resins! Geez if the painter hadn't of been so lazy I'd tell him to come back and take it all off.. I'm going to have to ponder this for a while now and try decide what to do :(
     
  8. niczilla@mac.co
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    niczilla@mac.co Junior Member

    Yep straight on the glass... If it was a spot where we knew it might be thicker we built it up with an epoxy - q cell - cabosil mix before we bogged over the top of that... Then a two pack high build primer is going down before the final 3 pack paint.. (But non of the painting is done yet)
     
  9. michael pierzga
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    michael pierzga Senior Member

    Sure..car bog will stick to a well sanded surface.

    But its inferior. Car bog is not waterproof like epoxy and it expands and contracts differently from the epoxy substrate. Print thru is common.

    Best practice it to use the same material as the substrate and to not use car bog underwater.

    Be sure that your car bog has a good barrier coat of primer.

    Review the applicators data for the International primer system. This is a very good primer system and is designed to be used as a NO SAND system when used with epoxy fairing compound. This saves very much time.
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    Don't panic, the situation is hopeless, but not serious. :rolleyes:
     
  11. niczilla@mac.co
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    niczilla@mac.co Junior Member

    Haha thanks for that mr efficiency... This was a refit that was supposed to take 3 months and were now looking at the 2 year mark of full time work on the boat looming so hopeless situations are quite serious!
     
  12. Mr Efficiency
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    Mr Efficiency Senior Member

    If it hasn't been overcoated yet, test the adhesion of the bogged areas, by a variety of methods, slide a sharp knife between it and the substrate, stick an old strap to it with epoxy and see if it pops off, even try vacuum suction, you never know till you try.
     
  13. niczilla@mac.co
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    niczilla@mac.co Junior Member

    Yeah that's a good idea, I might try a few of those tests
     
  14. Mr Efficiency
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    Mr Efficiency Senior Member

    Has anyone ever sanded car bog with those 3M flexible mesh sanding discs ( forget what it is called ) ? If the bog is softer than the epoxy substrate, and the discs work (doubtful), it could be a way to get back to a sound base without wrecking the thing.
     

  15. Saqa
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    Saqa Senior Member

    A sharp tap with a hammer can also delaminate it if its dodgy

    There is a disc in bunnings that looks like a bathing scourer on steroids. Works well to remove putty buildup in furniture without damaging the wood. Might work on the bog
     
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