Micheal,
I was about to ask if the boat were somewhere that freezes, you just
answered that.

You should know that it is -way- harder to effectively diagnose core
problems when the structure is frozen.

The up side is that, if you can warm the boat up in freezing weather, it
will dry out real fast (it still takes a significant time for the balsa
to completely dry) because the absolute humidity is sooo loow.

I like the sight you found, I saved it to pass to the next person to ask.
?Did you notice that the Acrylic and balsa are pretty close at the same
density?

The freeze-thaw cycle is part of what causes the delamination, but the
other bad-guy in the action is the original polyester resin that failed
to bond the core in the first place. What you have found is a common
problem. There is no easy fix. (I have been asked countless times if
it were posible to repair this be injecting some magic solution.) The
answer is know. I have seen the results of more than a few attempts.

If the core is not rotted, there is no reason you cannot open the area
up, dry it out and relaminate it. (I have done this successfully.) You
will find that those who worked from above have sand or shot bags all
around the room. It takes 1~3psi to effectively laminate. So, unless
you can unless you can jack the deck up 2~500lbs worth, find a vacuum
pump. Start shopping. It was more that a few years ago, but I bought
a pump and motor from a surplus house and screwed them both to a board.
I got the coupling parts from either Mcmaster-Carr or WW.Grainger (I
forget which) as well as a cheap A(15$) vacuum gage and a by-pass valve
to regulate the vacuum. All was less than 100$ cash-out-of-pocket.

Surplus Sales http://www.surpluscenter.com
C&H http://www.candhsales.com
American Scientific http://www.sciplus.com
Grainger http://www.grainger.com
McMaster http://www.mcmaster.com/

Remember - Thinking is the most effective and the least expensive thing
you can do.

Matt Colie

Michiel wrote:
Matt and everyone else who responded to my questions:

Thanks again for sharing your experience and knowledge. Very cool!


With regards to urethane, I ran into this:

http://www.azom.com/details.asp?Arti...ison_of_Core_1

Judging from this page polyurethane foam might not be very suitable
for a deck, although I'm not sure if the writer had the higher
densities in mind. It seems to me that the expansion of the foam would
help to make a good bond?


I did a few things this weekend to find out what state things are in.

I went around the deck with a rubber mallet to try to figure out the
extent of delamination. I think it's very widespread. Only at the
edges, things sounded hard. But I guess that it this point that's
good, because it'll make it easy to take out the old core.

I also cut out a small patch, from the inside. It was frozen when I
cut it. It's almost dry now. It doesn't look or feel rotten at all,
but it looks as if frost may have caused some damage (some cracks in
the wood). the balsa is still firmly bonded to the inner skin. It
seems the delamination is just between the outer skin and the balsa. I
can take a photo of this if it would help.

I think I may be able to reuse the existing core. The procedure I'm
thinking of now is: Cut out the inner skin, let it dry thoroughly,
Remove core in areas where deck hardware will be mounted and fill with
resin as suggested by another poster, then smear a fat coat of resin
around (be it polyester or epoxy), maybe thickened with some
microballoons and prop the whole mess up and then when it all dries
glass over the cuts.

Michiel
PS: vacuum bagging sounds like a wonderful technique, but I just can't
afford the investment now.

On Mon, 28 Nov 2005 09:24:46 -0500, Matt Colie
wrote:

If the core is not rotted, there is no reason you cannot open the area
up, dry it out and relaminate it.

While this is technically correct, once you've opened up an area I see
no point in "recycling" old balsa, given that balsa WILL wick up water
given the opportunity. It was used back in the day due to ease of
handling (cut into little tiles it will conform to complex curves in a
resin matrix) and low price.

But it's a wooden sponge. Lithium is the lightest metal, but you don't
see girders of it because its other properties are lousy for
structural applications.

Use marine plywood, encapsulated, for through deck mounting points,
and then use CoreCell, Airex, whatever for the core. They don't wick
up water and won't rot if wet. You may still have delamination if your
deck is leaky, but that's a function of the job you do next.

Along with others, I question the economics of doing this, but if you
like and want to sail the boat, you might as well do the best job
possible if you go to the trouble of taking the deck apart, which is
labour-intensive and a dirty, tedious job. The payoff is that when
it's all back together and the deck gear is backed by load-spreading
backing plates and sealant-covered bolts through epoxied holes in
encapsulated plywood, you feel very confident that the cleats will
give before the deck does, that you can jump on the deck without it
"giving" and that it will be dry and safer below, irrespective of the
weather.

I used to have fender washers. Now I have custom-cut (by me) 1/4"
backing plates on all through-deck gear. Nothing moves and only the
portlight (this winter's project!) leak. From that perspective, the 32
year old boat's "better than factory", because we have a very good
historical idea of the benefits and problems of balsa coring. And by
the way, there are some boats where thanks to attentive owners, the
balsa has never been wet, and the through-bolts pass through
water-proof epoxy "bushings". Those boats are absolutely sound.

But doing what is necessary won't add a penny to the resale value.
That's why in some cases it makes more sense to buy a beat-up bigger
sailboat with a delaminated, sad deck for a few grand and just strip
the top layer off the bugger and go for a total redo.

R.

http://www.cncphotoalbum.com/doityou.../rotrepair.htm

http://www.cncphotoalbum.com/doityou...rotrepair2.htm

Simple with great diagrams.

Mic wrote:

http://www.cncphotoalbum.com/doityou.../rotrepair.htm

http://www.cncphotoalbum.com/doityou...rotrepair2.htm

Simple with great diagrams.


-----------------------

REGARDING THOSE LINKS - we don't recommend 'squirting' any sort of
solvent containing liquid into any sort of confined space (such as
inside your deck).

Use 100% solids (solvent free) products and epoxies designed to bond to
wet or damp surfaces.

paul oman
progressive epoxy polymers

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