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  #21  
Old 05-16-2009
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The problem with filling the existing void with thickened epoxy, without opening up the deck's skin—either from above or below—is that you can't be sure you filled it completely. Also, adding thickened epoxy to it isn't going to return the deck to the same level of strength that re-coring it would do, and will make any proper future repair much more difficult to do.

Why not just re-core the area properly??? It isn't that difficult a task to do.
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  #22  
Old 05-16-2009
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Lightbulb Nondestructive repair

If it were my problem to fix, I would proceed as follows:

1. Confirm you have removed all the rot. A moisture meter will help, but the fact that color of the core is good at this point indicates you are there.

2. Dry with heat lamp until bone dry. May take a few days or a week. The moisture has to leave via the slot where the tang used to go, so it will take time.

3. Close off the lower side with vinyl rigging or electrical tape. Seal it well, to contain the epoxy during the fix.

4. Flood the cavity to soak the existing core with Smith's clear penetrating epoxy. CPES is watery-thin, extremely slow-setting, and will penetrate the existing core. It can also mix with minimal amounts of moisture. It will disappear into the balsa over the course of a day. You may have to re-fill the cavity a few times as it soaks in. The cavity will look almost empty after the CPES soaks into the core.

5. After a day, inject a good epoxy, such as West, thickened a bit with colloidal silica. Thin enough to inject, but thick enough to increase strength. It will crosslink to the CPES (which will not blush). Use a slow hardener to avoid exotherm heating, mix with as few bubbles as possible, and allow bubbles to rise in the mixing cup. Draw the epoxy (from the bottom, where there shouldn't be many bubbles) into an epoxy syringe, and slowly flood the cavity, allowing air to exit. If there is significant camber or angle to the area, you can apply vinyl tape to the lower edge to contain the fluid, or you can actually form a "cup" or "tube" (that is higher than the deck) with the tape. You may need to refill the void a few times as the epoxy soaks into the core and bubbles exit.

6. Result may have some minor bubbles, nothing structural, and it will be waterproof and solid. Probably harder than the surrounding balsa-cored area, and definitely stronger. Remove the vinyl tape.

7. Re-cut the opening for the tang, reinstall the tang, and bed the top to keep water at bay.

8. Finished fix will maintain the original skin (inside and out) and should outlast the rest of the boat.
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  #23  
Old 05-16-2009
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Quote:
Originally Posted by sailingdog View Post
Why not just re-core the area properly??? It isn't that difficult a task to do.
Because the repair will never match. But it may come to that.

EDIT: But you raise a very good point about it making a future repair difficult.

Last edited by jarcher; 05-16-2009 at 11:34 AM.
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Old 05-16-2009
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Quote:
Originally Posted by pvanv1 View Post
If there is significant camber or angle to the area, you can apply vinyl tape to the lower edge to contain the fluid, or you can actually form a "cup" or "tube" (that is higher than the deck) with the tape. You may need to refill the void a few times as the epoxy soaks into the core and bubbles exit.
Thanks Pvanv... There is some angle here. This is just aft of the forward hatch, so the deck tilts down a bit toward the bow at this point. I'm not following your suggestion as to how to keep the epoxy from running down away from the high side.

I only have a small opening, 2 in by 1/2 in, to work with, although I could open it up a bit and use a larger chain plate cover int he end.

How do I use tape to build a dam inside the core?
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Old 05-17-2009
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Lightbulb

Nothing against 'dog's idea of replacing the core, if you want is an end-product which is identical to the original -- and as vulnerable to rot as it was the day it left the factory, with a somewhat cosmetically-flawed top skin. Personally, I like my repairs to be at least a little better than the original work, if at all reasonable.

However, regarding "re-coring the area properly", my considered opinion is that there is no such thing as a "proper" balsa core, ever. Coring is a weight-saving and economy-minded stiffening technique. Balsa coring, with its inherent rot risks -- from even a minuscule leak -- is a cheap way to stiffen the laminate. Foam coring is a different story, of course, since foam doesn't rot like balsa. An epoxy-filled repair, even if it has a couple of bubbles trapped in it, will be much stronger than balsa could ever be. Properly done, it will exceed the life of the rest of the boat, even if the tang develops a leak in the future.

As for the damming technique I mentioned, I'm sorry if I wasn't too clear about how it's done. It's not done inside the core area, but rather on top of the deck. Might look kind of like a "volcano" or "funnel" of vinyl tape. Think of it as a "filler pipe" for the liquid. In fact, the initial epoxy repair can stand proud of the gelcoat, and then be sanded down flush before re-cutting the hole for the tang. End result is a solid plastic laminate, molecularly bonded to the internal balsa, and physically bonded to both the inner and outer skins. Very strong, and exceptionally waterproof. The nice thing about extending the form a little above the deck is that it provides a reservoir for the liquid epoxy. This allows gravity a little more room to float any bubbles up, and it also provides a reservoir so you don't have to refill the epoxy liquid as often during the time when it is soaking into the existing core.

I've prepared a lot of deck penetrations -- both new openings, and rot repairs -- with this technique, and they are all still in service. Some are decades old. I find this approach to be economical, easy, fast, effective, cosmetically invisible, and considerably better than the original construction.

If the finished surface isn't going to be covered, you can even add pigment to the epoxy, though it does tend to darken with UV exposure. The technique has a lot going for it.

I wouldn't repair an entire rotted-core deck this way. The cost would be too high, evacuating bubbles would be difficult at best, and it would be a lot heavier than the original. In that case, I would use foam coring, bedded in thickened epoxy. But for fixing rotted deck penetrations, I know of nothing that beats this method.
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  #26  
Old 05-17-2009
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Quote:
Originally Posted by pvanv1 View Post
Nothing against 'dog's idea of replacing the core, if you want is an end-product which is identical to the original -- and as vulnerable to rot as it was the day it left the factory, with a somewhat cosmetically-flawed top skin. Personally, I like my repairs to be at least a little better than the original work, if at all reasonable.

However, regarding "re-coring the area properly", my considered opinion is that there is no such thing as a "proper" balsa core, ever. Coring is a weight-saving and economy-minded stiffening technique. Balsa coring, with its inherent rot risks -- from even a minuscule leak -- is a cheap way to stiffen the laminate. Foam coring is a different story, of course, since foam doesn't rot like balsa.
Balsa cored decks are perfectly fine, if people took the care to seal any penetrations through the core material. Balsa wood doesn't rot if there is no water getting into it. It also has some characteristics that actually make it a better core material than foam in many cases. First, due to the end-grain nature of balsa used in core applications, it tends to keep any damage relatively localized for a fairly long time. A small leak into a foam core can often end up in large areas of delamination, due to the hydraulic pumping action that can occur with a foam core. Second, it has better shear and compression strength, when compared with most foam core materials. Third, it has higher-thermal deformation resistance than most foam core materials. If the hull is an epoxy resin laminate with a foam core, it can start to deform under the heat generated by long exposure to sunlight if painted a dark color.

Quote:
An epoxy-filled repair, even if it has a couple of bubbles trapped in it, will be much stronger than balsa could ever be. Properly done, it will exceed the life of the rest of the boat, even if the tang develops a leak in the future.
An epoxy-filled repair is usually far heavier and not as stiff as a properly designed cored-laminate of the same thickness. While thickened epoxy has great compressive and tensile strength, it doesn't have as much torsional strength as a properly cored laminate.

Quote:
As for the damming technique I mentioned, I'm sorry if I wasn't too clear about how it's done. It's not done inside the core area, but rather on top of the deck. Might look kind of like a "volcano" or "funnel" of vinyl tape. Think of it as a "filler pipe" for the liquid. In fact, the initial epoxy repair can stand proud of the gelcoat, and then be sanded down flush before re-cutting the hole for the tang. End result is a solid plastic laminate, molecularly bonded to the internal balsa, and physically bonded to both the inner and outer skins. Very strong, and exceptionally waterproof. The nice thing about extending the form a little above the deck is that it provides a reservoir for the liquid epoxy. This allows gravity a little more room to float any bubbles up, and it also provides a reservoir so you don't have to refill the epoxy liquid as often during the time when it is soaking into the existing core.

I've prepared a lot of deck penetrations -- both new openings, and rot repairs -- with this technique, and they are all still in service. Some are decades old. I find this approach to be economical, easy, fast, effective, cosmetically invisible, and considerably better than the original construction.
While you may have done a lot of repairs using this technique, and they may still be in service, it doesn't necessarily mean that this was the right way to repair them. How many of those repairs involved an area as extensive as what the OP is discussing... In many cases, what is easy and fast, is not always the proper or right way to do something, and often far less effective than doing it the RIGHT way.
Quote:
If the finished surface isn't going to be covered, you can even add pigment to the epoxy, though it does tend to darken with UV exposure. The technique has a lot going for it.

I wouldn't repair an entire rotted-core deck this way. The cost would be too high, evacuating bubbles would be difficult at best, and it would be a lot heavier than the original. In that case, I would use foam coring, bedded in thickened epoxy. But for fixing rotted deck penetrations, I know of nothing that beats this method.
If this had been caught earlier, I might agree with you that filling it with thickened epoxy would be a proper solution. However, this has gone far past a mere sealing of a rotted deck penetration at this point in time. Recoring the laminate there is the only proper solution IMHO.
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Last edited by sailingdog; 05-17-2009 at 11:22 AM.
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Old 05-17-2009
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Quote:
Originally Posted by pvanv1 View Post
As for the damming technique I mentioned, I'm sorry if I wasn't too clear about how it's done. It's not done inside the core area, but rather on top of the deck. Might look kind of like a "volcano" or "funnel" of vinyl tape. Think of it as a "filler pipe" for the liquid. In fact, the initial epoxy repair can stand proud of the gelcoat, and then be sanded down flush before re-cutting the hole for the tang.
Oh I see, you're building a funnel on top of the opening. So then you are thinking that when I pour the epoxy in, that it will fill up the cavity.

When I probe with the coat hanger, I can find small spaces that run further than the 3 or 4 inches of the void. I thought (possibly wrongly) that there were spaces between the pieces of core so that the core could curve. Wouldn't the liquid run down those?

If not I probably have more rot. Either way, it does not seem like the void inside is liquid tight, although I can't know without looking, and I am sure not going to pour any water in there to see if it leaks
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Old 05-18-2009
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If the rot is that extensive, I have to agree with 'dog -- open it up for a recore. An inch or two is one thing, but now that you're approaching half a foot, well, that's a whole different kettle of fish.

The non-invasive fix I suggested earlier would still work, but at a substantial epoxy cost, and a weight penalty, and it would also cause a hard spot in the deck. Plus, the longer the trip to the "good" core, the more the chances that the "pour-in-place" method will leave significant voids.

For rot this extensive, a recore will be the best solution.
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  #29  
Old 05-18-2009
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Also, opening it up and seeing the situation for what it is, first hand, will give you a lot more assurance about the repair being done properly. Fewer nagging doubts about what is going on inside the deck.
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Old 05-18-2009
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Yup, it looks like that's the only way to do it to be sure I got it all. From what I have read, the rot can keep on rotting if I don't get every last bit

I ordered the moisture meter, and I want to see where else I can expect the same issue before I start cutting open the deck. I'm worried I'll find it around all the fittings. I don't think I'm up for a recore of the entire deck, but we'll see how much there is.
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