Balsa core deck rot problem - SailNet Community

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  #1  
Old 03-18-2007
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Balsa core deck rot problem

I have been taking all the deck fittings off and re sealing the penetrations with SM Trip caulk. When I took off one of the mid deck cleats, I found quit a bit of waters and rot. My deck is a sandwich construction of Spruce, fiberglass, balsa, fiberglass, teak deck. I drilled out a 1" hole from the bottom and I can get my finger up inside where the balsa is and can feel the wet, rotten balsa for about 2" all the way around. I was told I need to get the moisture out first, then I can either fill the rotten area with West System or a product called Get Rot? All the other penetrations seem to be ok, so I don't think I have a huge problem, but want to fix this the right way. Any suggestions?
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Old 03-18-2007
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I had a similar problem. This is what I would suggest. Remove as much of the wet core as possible by picking it out. I used a bent coat hanger. Some suggest using a bent finish nail as a drill bit but I did not have good results. Get as much of the core out as possible. I used a hair dryer with a no heat setting and alternated between low heat and air until it was completely dry. I also drilled some small holes around the area from the underside to aid in the drying. After it was dry I taped off the large hole and mixed up some high density epoxy and injected it with a syringe into a small hole until the cavity was full. I had good results.
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I've used a small section of bent coat hanger (90 deg) chucked in a drill to remove such areas. The trick is to start small and slowly get bigger until you hit solid core, It took 3 different sized "Bits" then I used a shop vac to remove the debris, wiped down as much of the area that I could get to with acetone and filled with slightly thickened epoxy.
The area I worked on was about 4-5" in circumference.
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Old 03-18-2007
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You definitely want to remove as much of the rotten core as possible. While, GitRot is a good product, having a solid thickened epoxy in there instead is probably better for the deck in the long run. You also want to dry out the area as much as possible

I made up a few bits in the machine shop for ripping out the core that look kind of like a T with two sharp chisels on the ends of the crossbar. It seems work better than the makeshift ones, as it is better balanced and easier to control as a result.

Once you've reamed out the rotten core and dried out whatever good core is there... fill the area between the two skins with epoxy thickened with high density filler or collodial silica. Ollie's suggestion to use a syringe is a good one, as you don't want to have any air bubbles or voids. The way I've done it is to drill several small holes at around the edge of the reamed out area and then to inject epoxy into the holes until it comes out on the other sides.. The thickened epoxy serves two purposes: 1) it acts as a solid compression resistant filler for the deck fitting to be tightened down on—which balsa and foam core materials don't do well...they compress; 2) it acts to prevent water leaks around the fitting from migrating into the deck core and causing damage, core rot and delamination.
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Old 03-20-2007
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Thanks for the advice, I will get out the wet rotten core and look to fill the core with West System in a syringe. I am hoping the rotten balsa is only 4" to 5". Why do they use balsa for decks instead of Airex closed cell like I have in my hull? It seems like a problem waiting to happen.
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IIRC balsa is stronger than Airex physically... and end-grain balsa doesn't allow water to migrate along the interior of the core, which can happen with Airex. Also, balsa works better than some of the foams that were used as it doesn't lose strength under high heat, until a much higher temperature than most of the foams.

In one extreme case, on a dark blue boat, I could see the foam-cored deck depress when a 300 lb. crew walked across it after sitting in the sun through the early afternoon.
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[
In one extreme case, on a dark blue boat, I could see the foam-cored deck depress when a 300 lb. crew walked across it after sitting in the sun through the early afternoon.[/quote]

really? i just painted my boat dark blue! and it has foam core! was the deck blue or just the sides? this is a kinda disturbing thought
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Problem waiting to happen

Quote:
Originally Posted by dsbentley
Thanks for the advice, I will get out the wet rotten core and look to fill the core with West System in a syringe. I am hoping the rotten balsa is only 4" to 5". Why do they use balsa for decks instead of Airex closed cell like I have in my hull? It seems like a problem waiting to happen.
The use of balsa core in decking has been close to universal for all glass boats except the earliest designs...occasional wetness due to failing caulk is a common issue...now a cored hull, that is a problem waiting to happen...a firned of mine recently had to replace all the Airex core in his 42' hull, built by one of the best names in the business...
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The deck and the topsides were dark blue... and Chuck was carrying a full cooler of stuff... I bet if we had sprayed the deck down with cold water, you'd be able to see his foot prints...

I don't like dark colors for composite boats for two reasons...

One) if the deck heats up, composites can soften...this is particularly true for epoxy-based boats, rather less for vinylester and polyester resins. Epoxy tends to soften more than the other two resins under high temps.

Two) the other problem is that you can get fabric print-thru on dark colored boats. The reason this happens is that the resin in the hull or deck cures even more, due to the higher temps... and then you get the fabric showing thru the resin as a result.

IIRC, the deck on this boat had been re-cored and I believe they used epxoy resin over the foam coring material. Don't know what foam they used.
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