Matt,

Thanks for your comments.

I hope the original poster takes note of the steps required to correctly
install balsa core should he decide to go that way.

Brian Cleverly (to reply direct, replace the first "z" with an "n").

Matt Colie wrote:

Rodney, Brian and Marc,

Boy, I wish I had time to tell you all everything I've seen and done in
the last fifty plus years. But - let my start by saying that the
picture - though good - is a bad example. Just like so many things,
when it was first done, builders didn't understand how much trouble they
were starting.

Many builders used endgrain block filler like that. The only ones that
made it work use a filled area around each block the sequester them.
The companies the used block without that left a gap between the blocks
that served as a conduit for any water that got into the construction.

They builders that used bound sheet of end grain balsa did a little
better, but since those where largely laided up construction, the inner
layup usually left at small gap the the core edge that again was a good
conduit for water.

There were places in my current boat that had marine plywood for a high
stress area in a layup of balsa core. In some of those where the
bedding on deck had gone bad, the plywood was shot, though the adjacent
balsa core was saturated and delaminated it was still there. I could
have dried it out and reused it.

Closed cell foam is no answer either. I have a Whaler sailing dink out
here that was mistreated and now weighs in at 300+. I have also ben
contracted to repair laid-up foam core structures that were delaminating
because of water intrusion damage.

The only answer I have come up with that makes any sense is:

Do not trap water.

If there might be a place it can get in, make sure it has a way out. Do
your best to keep it out, but the thing that caused the problem was the
the water stayed in. Drain holes in the inner deck skin will stop the
migration of moisture in the core right there.

If you are going to rebuild a cored structure, learn all about vacuum
techniques for laminating. That is the only way that I have found to
create the solid lamination required.

Matt Colie

Rodney Myrvaagnes wrote:
On Sat, 28 Feb 2004 18:24:10 -0800, Brian Cleverly
wrote:



Rodney Myrvaagnes wrote:

On Fri, 27 Feb 2004 23:10:29 -0500, "Marc Beroz"
wrote:


Rodney,
What do you suggest I use for core?
Marc


Closed cell foam or end grain balsa, if bonded properly, will isolate
places where water penetrates.

I agree with the foam, but you are dead wrong about the balsa... I've
replaced the balsa core in many decks where the endgrain balsa has acted
like a sponge and totally rotted out.

Don't believe me ? For an example, take a look at:

ftp://ftp.sailnet.com/pearson/pearso...ted%20core.jpg


Pearson used balsa in non-end-grain orientation in early boats.

I have a 24-year-old boat that has suffered numerous insults and
repairs and is still strong and just passed a survey. It is cored with
Baltek end-grain.

If the end-grain core is not bonded to the outer layers, water can
travel between, as it can with any core. It does not travel fast
across the grain inside the wood.



Rodney Myrvaagnes J36 Gjo/a


MOM CASTS TOT IN CEMENT

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