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In a message dated 9/21/04 12:01:20 AM, Keith writes:
> <<The thing you have to be careful with on balsa coring are the hull
> penetrations. Balsa will rot if it gets wet. To do them properly, the hole
> should have been drilled out, then the coring removed for an inch or so and
> the gap filled with epoxy.>>
>
End grain balsa is a high quality material that was used as the hull coring
of premium boats. The balsa was sawed into little blocks about 2" square and
1/2" thick, then attached to a scrim so the material could be draped across
curved surfaces. Because water penetrates mostly along the wood grain, rather than
across the grain, end grain balsa is more resistant to rot than most wood
coring. As Keith pointed out, the weak spot of balsa coring is hull penetration.
There is the possibility of local rot, but more important is the crushing of
the core material if the fastenings are snugged up too much. This produces a
weak spot in the hull and an insecure base for the fitting. The cure for
avoiding rot and crushing is the same. Drill the hole for the thru hull or fitting.
Insert an L shaped drill bit through the hole and spin it around for a while,
pulverizing the coring under the hole. A sharpened 1/4" Allen wrench works
fine. Blow out the sawdust and pack the empty area with epoxy or epoxy putty. Then
attach the fitting. This provides a firm base for the fitting and
simultaneously seals the balsa coring from future water penetration.
End grain balsa is a great core material. The reason why it is not used too
much anymore is that it is much more costly than foam alternatives.
Larry Z
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