Dealing with a soggy cockpit sole - Page 5 - SailNet Community
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post #41 of 52 Old 06-29-2011
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The other issue is that plywood, once penetrated by moisture tends to migrate the moisture laterally thoughout the structure due to the orientation of the plys... End grain balsa at least tries to limit it to the penetrated segment, to a point.

Ron

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post #42 of 52 Old 06-29-2011
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The other issue is that plywood, once penetrated by moisture tends to migrate the moisture laterally throughout the structure due to the orientation of the plys... End grain balsa at least tries to limit it to the penetrated segment, to a point.

Ron

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post #43 of 52 Old 06-29-2011
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"why would they bother with the sandwich construction throughout then?"
Because IF a conventional sandwich is done correctly, it is light and strong and doesn't admit or trap water. Done incorrectly or damaged is a different story. Some builders used plywood (marine or Brunei) despite the extra weight and perhaps extra cost, because it is stronger.

Every engineering and construction choice is a trade-off. Sometimes they make the one you need, sometimes not.
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post #44 of 52 Old 06-29-2011
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Quote:
Originally Posted by sandycohen View Post
I had my cockpit sole 'recored' from underneath - i put 'recore' in quotes because we didn't put another skin on the bottom - cut out the bottom skin, ground out the balsa core, and then epoxied in solid 1/2" marine grade plywood, saturating all surfaces and penetrations with epoxy. What's the point of having a fiberglass skin underneath something when no one ever looks at it from that angle, and it's just a way to trap moisture?
Unless you laid at least some glass overlapping at the edges of the plywood underneath, this solution is not the best. Epoxy is a good adhesive. But it is just that. Using a thick layer of epoxy is not a substitute for a structural, load carrying element such as the fiberglass. Eventually it will get dry and brittle. Don't be surprised if you see cracks/tears at the edges of your sole one day. After going through all the trouble of recoring, why skimp on the last step? The argument that the core will stay dry this way is not a good one IMHO. Just correctly seal everything and it will stay dry.

You need fiberglass underneath to bear the tensile strength that occurs when you step on the sole. Believe me, manufacturers are not using sandwich structure to save on the cost of plywood.

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post #45 of 52 Old 06-29-2011
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The purpose of a core in a deck is not in any way to add strength by itself but to separate the cores, both of which are required. Similar to the "I" beam previously mentioned. Some hi-tech decks use a nomex or paper honeycomb which has almost no weight and no strength itself until firmly attached the the skins on each side. They come closest to the ideal a core that adds no extra weight.

Plywood makes probably the worst core material possible for reasons of weight where it is not wanted, water migration, and shear strength. Balsa is the best (affordable) core material because of its light weight and great compressive strength as it is end grain. It also conforms to curves easily as it is composed of separate squares of balsa on a scrim material. Water migration with balsa is limited. The soggy decks you read about didn't happen in a year or two - they sometimes had decades to ferment and rot.

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post #46 of 52 Old 06-30-2011
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Job finished and updated!
I'm late to the thread but just had to say GREAT JOB! I look at the photos and am in awe of the amount of labor I see (and am thankful it was not me doing it!!). I have done a lot of glass work and doing anything "upside down" is always very frustrating.

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post #47 of 52 Old 06-30-2011 Thread Starter
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I'm late to the thread but just had to say GREAT JOB! I look at the photos and am in awe of the amount of labor I see (and am thankful it was not me doing it!!). I have done a lot of glass work and doing anything "upside down" is always very frustrating.

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Thanks! Just updated with the finished job yesterday so you aren't late at all.

My boat rebuild/sailing blog:
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post #48 of 52 Old 06-30-2011
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It looks great but you sure did it the hard way.

Brian
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post #49 of 52 Old 06-30-2011 Thread Starter
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It looks great but you sure did it the hard way.
heh, I'm learning as I go. Mistakes will be made, but at least others can learn from it as well thanks to the interwebs.

As long as I do the actual work well, I'm happy with it.

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post #50 of 52 Old 06-30-2011
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underneath

Great job on the repair!!! I have done major recoring efforts from both below and above. Personally, I have found it to be 6 one way and half a dozen the other as far as time and effort. The payoff for the underneath method is of course that you don't have mess with the cosmetics which is a big time saver and, to me, that is the most time consuming and skill-heavy part of the repair to do right. To me it is especially worth the effort to go from underneath if you have a molded non-skid pattern you want to preserve or you don't have the skills necessary to do a proper cosmetic job from above. If you are planning to repaint the deck anyway than doing a job from the top is a no-brainer. Couple of suggestions if doing it from underneath (without vacuum bagging). First, stick the balsa up in smaller sections. After wetting out and filling the kerfs, place the blob of thickened balsa in the center of the section and press on so that the epoxy is forced out to the edges--you don't want voids and smaller pieces are just less nerve-wracking. Scrape off the excess and move to the next piece. Use enough silica in the epoxy mix so that it is really thick and bracing requirements are minimal (use bent furring strips for a cheap brace, if required at all). Second, timing is everything. Paint or roll on the epoxy before adding the cloth...let it kick enough so that it is sticky and then apply the next layer of cloth so you don't have problems with sag. Alternatively, you might try stapling the cloth up with stainless or monel staples into the balsa, overcoat any exposed staples with epoxy at the end.

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