Recoring soggy balsa decks

[John in Connecticut]

Tim;

I see you used plywood and am wondering if you considered the "end grain" cardboard that West system sells? I used some for a deck repair (stern) on my Celebrity daysailer seven years ago and it is holding up well. My little daysailer (19 foot 10 inch) I felt was sensitive to weight on the topsides and the cardboard was virtually weightless, much like the balsa. I'm planning to do the bow and side sections this winter and would like to hear the your's and the Board's collective wisdom,

Thanks,

John in CT

[Dave, 397]

I'm liking the Nida material an awful lot...it is very lightweight and won't ever care if it gets wet. It does use quite a bit of resin, which I was concerned about from a weight standpoint. After weighing out a bit of the sodden balsa I have removed, I was no longer concerned at all!

I do not think it is realistic to expect that any balsa-cored boat 10 years or more is not going to have some water saturation...it can take a long time before that turns into delam or rot, and until then it feels and "sounds" just fine in most cases...so I think that in the real world a lot of boats are packing more weight.

I have been messing around with a paper-based material as an alternative to coremat, and it seems just great as long as it is well and thoroughly wetted out so that it actually soaks thru...thinning the epoxy seems to be key to do so. I guess I have a similar worry about corrugated cardboard-type stuff, not that I have seen or used anything like that.

At 60.00 a sheet, the Nida's a great deal---you might look into it.

Dave

[Tim]

John,

I haven't seen the product you're talking about, so can't really comment one way or another. I only used the plywood because I had the free supply that came with the boat. It did the trick, but I would not willingly choose it from scratch. With a product like the end grain cardboard marketed by a respected company (West System), I would guess that there is probably some substantial research and testing that has occured. I bet they have reference material available on how they developed the product, as West System may be one of the more scientifically backed products out there.

Any type of deck core requires complete isolation from all penetration points in order to have a first class job. I believe that this, coupled with quality resins and thorough bonding, is the key to longevity of any core material. DIYers can do this very easily, as it costs only time and thought. You rarely see it in a production boat because of the time involved. Time=money in a production setup, so usually this corner is cut, meaning more margin for the company and/or a lower price for the consumer. High end builders do not forgo this step, but you pay dearly for their products.

Most balsa core failures occur not because of an inherent problem with the material--end grain balsa blocks actually resist water infiltration from the sides very well--but because of improper installation techniques. I think balsa is falsy vilified, when the true culprit is poor quality installation and maintenance. It always comes down to keeping the water out. This goes for any core. Obviously, it seems logical that plastic and some foam materials might be inherently more resistant to moisture. Perhaps so, but time has already shown us that certain foams fail under differing circumstances, and water, when in an entrapped environment, is one of the most powerful forces there is. Never say never, I say. That said, I think Nida Core is a good product and will probably use it when I have the opportunity, but I won't discount balsa either--it makes an excellent sandwich construction. And the same installation techniques apply to either product. If you follow these basic rules, I think core failure is unlikely.

Whatver core you use, take steps to ensure proper bonding and isolation. Proper bonding comes from using epoxy resins for adhesive putties and ensuring, at the time of installation, that the material is well bedded on both sides with no voids. If using a contoured core material (most are), ensure that the resin/adhesive fills the kerfs between the blocks. Most water migration occurs through these kerfs, and these, along withpoor bonding techniques, lead to many failures over time.

Finally, solid glass around all hardware locations is the best way to ensure isolation. If that seems a step too far, then at least plan on overdrilling every hole, filling with epoxy, and then redrilling the smaller fastener hole through the center of the epoxy plug to prevent the inevitable leakage from entering the core.

I say if you're happy with the results from you previous use of the cardboard, go ahead and use it. What better proof is there than that?