[Rhodes22-list] ...on spray foam and other musings....

Rob Granger rgranger at sbc.edu
Mon Feb 13 21:58:22 EST 2012

Okay I didn't want to seem heavy handed when I stated before that I was
"almost certain" that Great Stuff is closed cell because there is a lot of
controversy on this topic and to be fair, not all spray foams are the
same... but I'm a chemist and I felt it was necessary that we get this
straitened out since many of us are DIY boaters...  so on the topic of
spray foam

Some spray foams are latex and therefore open celled (DO NOT USE LATEX
SPRAY FOAM ON YOUR BOAT) but Great Stuff expanding spray foam is a
polyurethane-based foam and not a latex foam.  So unlike the latex spray
foams it is *closed cell*.   And you should not be afraid of it absorbing
water.  It will (however) stick to the hull like ... well a polyurethane
glue (think Gorilla glue).  So the bag idea is the way to go if you ever
want to get it out again... or line the area with visqueen before you
spray.  I've used both approaches and they both work fine...  I can post
pictures if anyone wants to see the results of the bag or visqueen

So to clarify, polyurethane foam (Great Stuff)  is *closed cell*... so it
is fine to use on your boat, even in low spots.

The pink and blue foam boards at Lowes and HomeDepo are also great to use
for floatation foam.  They are *extruded* polystyrene and so they will not
fall apart into tiny little balls that make a mess everywhere... (Iike
cheap styrofoam will).  I have about six 3" boards cut up and crammed into
my MacGregor 22'.  And all of the little left over pieces are in a bag,
crammed into a tight spot and filled with spray foam (along with some
packing peanuts I got in Christmas boxes this year).

A note on packing peanuts.  They're now two kinds.  The old-school kind are
made of styrofoam.  Those are fine to use on a boat.  The other type are "*
green*" and made of cellulose.  The cellulose peanuts will dissolve in
water.  Obviously you do not want to use those.  It is easy to tell which
type you have.  Drop one in a glass of water and wait a bit.  Or you can
bite one  :-)

If you are skeptical about the closed cell nature of Great Stuff expanding
foam...(and it is not a bad thing to be skeptical) you can read about it on
the Dow Chemical site... you wont hurt my feelings if you do... I promise

Here is the link to the Dow Chemical site


my 2 cents.

... the other Rob

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