I was doing a "burn" today.  We had a wild storm last night with
thunder storm after thunderstorm, a total of 1.8" of precip, including
some rather large hail.   I lit my huge incinerator (3' diameter 5'
high, half inch wall steel pipe, with a powerful fan), and began hauling
out a few months accumulation, plus a lot of stuff I'd weeded out of my
house and shop.   Quite impressive to see, no smoke after the first few
minutes, and fire climbing 12' or so into the sky.  I never burn unless
it's wet out.

    In  the process, I unearthed a piece of 1" XPS that I'd forgotten I
had.    It was 3' long, by 8" wide.    I decided to do a bend test, by
wedging one end against the wall, and pushing on the other so that there
would not be a specific stress point.   The foam arched up, 4", 6", 8",
9", and I was bracing for the inevitable failure from about 6".   It
finally popped after arching up to 9.75", measured with a tape measure
under the arch.

    Nine inches in 3' of length, is a LOT of curvature........ I've
forgotten much of my geometery, but that's an impressive radius for a
solid unscoured piece of foam.  Easily enough to plank a hull...... if
you were so inclined, or do a bridge deck cabin roof, etc.  In fact
there are few places on a boat where one would need to bend a radius
much tighter than that.  One characteristic of XPS is that the thicker
the foam, the less bend tolerant it is.   I have some 1.5" XPS also
(both blue two pound Dow Corning).  I know it wouldn't go anywhere near
that far, but it's full sheets, and I have no intention of sacrificing
it to science ;-)

    One crazy thought I've had with XPS is to hit the foam very lightly
with a small shop sand blaster.......... very very lightly, to create a
rougher surface prior to infusion.  Needless to say it won't tolerate
much at all.  I tried a piece in an abrasive blast cabinet, at a
friend's shop, but the media he was using was extremely course and
aggressive silicon carbide... and quite dirty. All it takes is a "flash
pass" to rough the surface.... about like it takes with a torch to burn
the hair off your arm.  This would hugely improve adhesion, if one
thought it was necessary.

    I am by no means advocating XPS for everything, nor have I
ever....... I think I've made that pretty clear.  I feel it does have a
legitimate place.

H.W.

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