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Old 11-04-2018, 01:13   #1
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Fixing a broken fiberglass joint

The joint joining interior bunks to the hull seems to have partially failed in this 1980s fiberglass boat.

No sandwich construction anywhere near. How would one go about fixing this? Anything special to look out for?

Should the top of the shear be removed (e.g. with a saw blade), the whole area cleaned properly and then sanded a little bit by hand for better grip. Then epoxy + fiberglass mat + epoxy?

Also links to relevant guides/howtos appreciated.

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Old 11-04-2018, 02:50   #2
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Re: Fixing a broken fiberglass joint

Looks like the tabbing has delaminated. Everything that's not well-stuck needs to go. You may be able to grab it with a vise grip and just rip it right off. Otherwise you'll have to grind or cut. Once you're removed everything that's not well-adhered, sand to bare glass before taping again. Use the resin/glass system of your choice, just be careful not to begin another emotional polyester vs vinylester vs epoxy thread--there's plenty of those that can be searched.
Good luck
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Old 12-04-2018, 04:17   #3
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Re: Fixing a broken fiberglass joint

Greetings and welcome aboard the CF, Violet.
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Old 12-04-2018, 05:01   #4
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Re: Fixing a broken fiberglass joint

I would not condemn that right off the bat based on what's visible in the picture. It may just be the edge of the tabbing. I'd work a putty knife up between it and the hull and see how far back it goes. If it's only and inch or so I'll bet it's been that way since the boat was built and I'd leave it as it is. If it's more severe I'd do as Benz suggested.

I'd be far more concerned about that thru-hull and seacock though. I'd replace that immediately lol.
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Old 12-04-2018, 06:37   #5
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Re: Fixing a broken fiberglass joint

It’s like that on both sides and the vertical joints as well in the 2 corners?
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Old 12-04-2018, 08:00   #6
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Re: Fixing a broken fiberglass joint

Remove all delaminated tabbing. Clean area thoroughly with TSP. Grind area to be re-tabbed. Apply biaxial cloth with mat using epoxy.

Replace crappy gate valve with new sea cock.
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Old 12-04-2018, 10:27   #7
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Re: Fixing a broken fiberglass joint

I had a lot of these to deal with. Here's how I was taught, by an actual boat builder, to do the structural bulkheads.
1) Cut out all the old delaminated material. If not now, you'll be re-doing it later. Rough up te surfaces with about a 36 grit grinder.
2) Mix some thickened polyester (or Vinylester) and use a cone of wax paper, with the tip cut off, much like a cake decorator would use, to apply a fillet into the corner between the bulkhead and hull. Tool it off into a nice radius; I used about one inch.
3) Cut cloth into strips, ON THE BIAS, so they'll follow any curvature and not pucker. 1st strip down will be 4 inches wide, next strip 6 inches wide, 3rd strip 8 wide. (2 or 3 strips will be plenty if this is non structural).
4) Have the strips cut so you can lay them in before the fillet is fully cured.
While you're in there, get rid of that damned gate valve.
After 10 years of heavy use, not one of those joints has failed.
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Old 12-04-2018, 13:53   #8
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Re: Fixing a broken fiberglass joint

One more vote for leave it alone, if it really is just the bunk face tabbing, isn't moving now, will not be subject to 'excessive' loads in the future and is 'non-structural' - but you need to know for sure it's not part of the hull supporting structure.

With that silly gate valve and that even sillier rigid plastic pipe leaving it, I'd say you may find far more serious issues elsewhere. I tend to agree with almost everything I've read in Don Casey's reference book, 'This Old Boat', which will help identify, understand and fix many of these sorts of issues.
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Old 12-04-2018, 14:03   #9
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Re: Fixing a broken fiberglass joint

Quote:
Originally Posted by NevisDog View Post
...isn't moving now, will not be subject to 'excessive' loads in the future and is 'non-structural'....
Wrong.

That tabbing to the bunk is what is supposed to prevent the hull from oil canning, which makes it structural. Obviously it has been over-stressed from just such loads.
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Old 12-04-2018, 14:32   #10
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Re: Fixing a broken fiberglass joint

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Originally Posted by Terra Nova View Post
Wrong.

That tabbing to the bunk is what is supposed to prevent the hull from oil canning, which makes it structural. Obviously it has been over-stressed from just such loads.
Not necessarily. Tabbing can be over-stressed for example by dropping something heavy on the bunk - a one-off event, never to be repeated. It would be very surprising if any structural element that close to the transom could possibly be stressed to the extent of tabbing failure, but sure it's possible - anything is possible - which is why I said check it out.

Oil-canning that close to the transom? Really???
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Old 12-04-2018, 17:22   #11
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Re: Fixing a broken fiberglass joint

Exactly! Fix the darned thing
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Old 13-04-2018, 03:38   #12
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Re: Fixing a broken fiberglass joint

Bloody hell Nevisdog remind me never to get you to doing any glassing for me. Dropping something heavy from a bunk should not cause the tabbing to delaminate like that. I would expect to be able to keep dropping my esky in there and never have an issue.
I reckon just cut away all the delaminated glass, grind it all up and put some new glass tabbing in. No big deal and if you use polyester resin you could have that all repaired in 4 hours. Then after lunch when it is dry give it a quick touch up with the grinder and paint it out with flo coat. All done, no drama except for a bit of itching if you do not wear disposable overalls!
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Old 13-04-2018, 08:24   #13
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Re: Fixing a broken fiberglass joint

The loose tabbing shown in the picture is a classic example of the weak secondary bonds formed with Polyester resin.
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Old 13-04-2018, 08:27   #14
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Re: Fixing a broken fiberglass joint

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Originally Posted by guyrj33 View Post
The loose tabbing shown in the picture is a classic example of the weak secondary bonds formed with Polyester resin.
That it is.
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Old 13-04-2018, 08:45   #15
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Re: Fixing a broken fiberglass joint

Quote:
Originally Posted by Suijin View Post
I would not condemn that right off the bat based on what's visible in the picture. It may just be the edge of the tabbing. I'd work a putty knife up between it and the hull and see how far back it goes. If it's only and inch or so I'll bet it's been that way since the boat was built and I'd leave it as it is. If it's more severe I'd do as Benz suggested.

I'd be far more concerned about that thru-hull and seacock though. I'd replace that immediately lol.
This ^^
Force a chisel into the gap and see if it's actually loose or not. My guess is not. If it is unattached, all the tabbing in the boat may be!
IF you need to do more, grind it to bare glass with 40 grit grinder and glass over it with more tabbing, assuming it is bonded to the hull and cabinetry except a bit of the edges.
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