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Old 09-02-2016, 12:41   #16
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Re: Replacing wet balsa core

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Sometimes those egos are well deserved. I'm grateful that some folks keep posting even after they're constantly attacked for no apparent reason.
Exactly....Thank you Minaret, for taking the time to help others...in spite of the BS from a select few.
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Old 09-02-2016, 13:06   #17
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Re: Replacing wet balsa core

I've been on and off this site for a number of years and minaret is one of a select few regular posters that comes across as being someone that has genuine expertise in the topics to which they contribute. Having said that, sometimes I think there are alternative solutions that, perhaps not 100% as good in all aspects, would be satisfactory in a particular situation. In this respect, I'd think either minaret's or guyrj33's solution would work. The former because it is stronger and the latter because it is cheaper and it is, arguably, easier to work with polyester than epoxy. I'd personally suggest vinyl-ester as a compromise if push came to shove however.

One suggestion that has been made was not to worry about using a hard core material under loaded deck fittings (which neither of the guys above suggested). DO NOT DO THIS! You can use backing plates until the cows come home (which you should anyway) but you can't stop the fitting itself compressing the substrate through the thick top skin. Whilst this won't necessarily lead lo failure, it can lead to indenting of the surface and/or spider cracking.

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Old 09-02-2016, 15:18   #18
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Re: Replacing wet balsa core

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Wet balsa core is along the genoa track on C&C38 mk2 from 1976.
area is 12" wide and 14 feet long. Top laminate is 3/16" thick and balsa is 1/2" thick. That 12" width is pretty much the extent of rot as deck tapers at either end.
Additional comment... make sure you know how the water got in. This is a pretty big area that was consistently wet. If you think it was all coming in from the genoa track bolts then I think you are in good shape to proceed with lots of good advice from this thread. If, however, the moisture is coming from other poorly mounted hardware, a window, the toe rail, etc. then that has to be fixed first or you'll just have move problems. Water can travel from the cabin top to the decks through layers of laminate so it could be coming from an unexpected source.

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Old 09-02-2016, 15:32   #19
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Re: Replacing wet balsa core

Member Galleries - Cruisers & Sailing Photo Gallery


This is the link to photos on this site. We have replaced much wet balsa from inside. I use ONLY US composites 635THIN resin and compound it with their 3M microballons to make a syntactic foam slurry. Lower cost than any other supplier and easy to use. This is pumped into the prepared cavity using calking gun tubes we fill & refill. (McMaster Carr)


I use a 3-inch hole saw fro inside the cabin to expose the wet balsa. (we hve a headliner to cover the repair) Dig out the wet balsa and keep making holes until you find dry core. Cover the holes with a sheet of heavy fiberglass applied using release film over light plywood and props to hold it in place. What is left is a hollow defined by the inside skin and the outside deck. If you are doing the repair, fix it with materials that will never be wet again. This cured slurry is massively stronger than balsa and totally waterproof.


Epoxy :*Epoxy Resins and Hardeners


Fillers
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Old 09-02-2016, 21:55   #20
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Re: Replacing wet balsa core

I know it is a bit late but I am with Nick 58 & doing it from the underneath if at all possible. Yes it is bloody awkward using a grinder & dremel upside down and the glassing can be frustrating. But the deck gel coat is never touched and you can use the Genoa track bolt holes to help hold the new core against the deck layer of glass. I have done this on a number of yachts and always curse myself for getting involved!
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Old 09-02-2016, 22:28   #21
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Re: Replacing wet balsa core

Doing a repair from underneath is just the pits. About the only advantage is that the top skin can be left intact, which is not that big of an advantage in a lot of cases. Everything else about it sucks.

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Old 10-02-2016, 00:39   #22
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Re: Replacing wet balsa core

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I know it is a bit late but I am with Nick 58 & doing it from the underneath if at all possible.
Looking at the pics in post #1 I think the op has already removed the top layer of glass.
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Old 11-02-2016, 17:49   #23
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Re: Replacing wet balsa core

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Looking at the pics in post #1 I think the op has already removed the top layer of glass.
This is true. The OP appears to be committed to a top repair plan. Still, the materials and methods I propose may be helpful & if the OP needs to do a future repair, the bottom approach may be useful. I would always recommend the US composites 635 THIN as the go-to material and this job is no exception. Pull out the wet stuff and wait for the lower glass to dry. Pour in the Epoxy-microballoon slurry and add a glass mat or mats, additional resin and release sheet & thin flex plywood top layer with a little weight. Definitely easier repair from the top but the finishing artwork is more difficult. Follow my original link to photos and see the rudder repair using the same materials and carbon fiber vacuum bag skin.

I'm sure the OP will get this done OK, but using the right stuff and methods makes sure it is only done once.
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Old 11-02-2016, 22:33   #24
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Re: Replacing wet balsa core

Two more cents:

I've got a surveyor jumping up and down telling me not to use epoxy to rebuild a deck that has had "wet core issues" and wet for not the reasons you'd expect, but nonetheless it was once wet.

Says he has seen too many decks that were redone in epoxy, and had issues. Something about really getting them dried, and hence epoxy doing well in that application.

May not be your issue, however I tend to like to benefit from others experience, which is why I'm on the forum. And may be some have had good result with epoxy, but I'd rather not risk it. Been through enough hell already.
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Old 12-02-2016, 05:54   #25
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Re: Replacing wet balsa core

Bonding issues with epoxy are often created by neglecting to water rinse the blush from cured epoxy. I've learned that removing the blush sometimes requires some vigorous scrubbing with a 3m kitchen pad.

The blush is water soluble, so acetone isn't a substitute for water. And sanding before the water rinse forces the blush into the surface making removal more difficult.

Except for a special laminating hardener, all the West hardeners blush, with varying degrees dependent on temp and humidity.

Blush removal is a pita, but I've learned to live with it during my refit. However, I now generally use the non blush hardener (and still often rinse; some habits don't die).

And yes, I learned this the hard way.

This forum has been a great resource for me, and I'm grateful to those folks who take the time to share their experiences, especially those employed in the marine trades. They deal with a depth and breadth of issues - and resources - that I'll never encounter in my more focused project.

In the end, I mix the varied comments here with my own experience and research and take my best shot.

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Old 12-02-2016, 06:56   #26
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Re: Replacing wet balsa core

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Originally Posted by Reefmagnet View Post
One suggestion that has been made was not to worry about using a hard core material under loaded deck fittings (which neither of the guys above suggested). DO NOT DO THIS! You can use backing plates until the cows come home (which you should anyway) but you can't stop the fitting itself compressing the substrate through the thick top skin. Whilst this won't necessarily lead lo failure, it can lead to indenting of the surface and/or ...
What he said. Backing plates are good for vertical load (genoa track) but if there is a tipping load (cleat) it will crush on one side. Additionally, plates can be tough to fit to curved surfaces and near corners, where extra laminate is a better solution (combined with a smaller plate).
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Old 12-02-2016, 07:06   #27
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Re: Replacing wet balsa core

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What he said. Backing plates are good for vertical load (genoa track) but if there is a tipping load (cleat) it will crush on one side. Additionally, plates can be tough to fit to curved surfaces and near corners, where extra laminate is a better solution (combined with a smaller plate).


No, Coosa will not crush. Not anymore than marine ply would. It is built in a hydraulic press at 60k PSI.
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Old 12-02-2016, 11:36   #28
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Re: Replacing wet balsa core

S/V Trio,
Thanks for sharing about cured epoxy blush that needs to be removed with water, and the blush not being properly removed as a possible epoxy bonding issue for subsequent layers. That's helpful.

I gather the comments the surveyor shared to me to not go to an epoxy solution to replace the deck, had more to do with getting a deck absolutely dry after water intrusion, and hence felt polyester was more forgiving than epoxy in that regard, even tho in theory epoxy has stronger adhesion properties. That plus the number of epoxy repaired decks he subsequently found in failure. His words and opinion. Obviously, if someone here has an epoxy repaired deck that is in great shape, then luckily doesn't apply.

I don't need to worry about drying, there's been lots of natural "bake-out" time. Others might need to though.

Aside from time, and the right natural conditions, what do others do to "make sure the deck is completely dry" before proceeding?

Thanks for sharing everyone.
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Old 12-02-2016, 14:13   #29
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Re: Replacing wet balsa core

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Originally Posted by BigSmile View Post

I don't need to worry about drying, there's been lots of natural "bake-out" time. Others might need to though.

Aside from time, and the right natural conditions, what do others do to "make sure the deck is completely dry" before proceeding?

Thanks for sharing everyone.
Old man time, but to hasten the project fans and heat can't be beat. I made up a simple rig using some old computer fans I scrounged up. Server fans are the best because they're smaller and blast out the air. Although any suitable fan will do just to keep air circulating. I don't have to worry about heat where I am, but I'd guess you'd need to introduce that too. Bigger the job, the bigger the heat and fans needed.
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Old 12-02-2016, 15:19   #30
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Re: Replacing wet balsa core

I am refitting my Alberg 30 and was working my way around the deck replacing rotten core until cold weather hit.

I used balsa in lazarette area. Anywhere a stanchion or anything I knew would pass thru the deck I used G10 fiberglass board in place of the core. I did this for 2 reasons. One was to keep water out of new core forever... the other was to make sure there would be NO compression once the fitting were put on.

there are some photos here on my blog that show the new core with G10 board where the rear hatch hinges and chainplate will pass thru the lazarette deck area.


Adventures of Salacia: Alberg 30 refit: A Small Bit of Deck Progress and a Whole Lot of Nova Scotian Maritime Adventure

For some reason when my boat was built they used different thickness of core in different areas. This caused a slight problem so onn the side decks I did move to Core-Cell A500 foam coring only because balsa was not available in 1/4" from local supplier. Core-cell was easier to work with but did cost about 25% more.

G10 board is expensive if you buy large chunks of it but suppliers like Norva Plastics(on Ebay) sells odd sized scrap pieces perfect for what I am using them for. Best of all its cheap! For $60 I bought enough for the deck repairs and backing plates.

Hope this helps
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