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

[Goodness]

Thanks Rob.  I am building out a 43' steel sailboat hull.  I am finishing the final interior epoxy coats now then i will spray closed cell polyurethane foam all over the interior hull over the stringers and ribs.  Then i have read i should spray a fire retardant elastomeric paint over the foam to resist ignition in case of an interior fire. This foam will insulate as well as contribute to the oxygen barrier of the epoxy.
what kind of foam did boston whaler use in their hull construction?  My friend has a bw dinghy hull that weighs about 300 pounds! Thats like 20 gallons of absorbed water!  My understanding of closed cell foam is that if it is cut after spraying it will absorb some, but i am not sure how much.  I think the Rhodes has the good stuff in there like the foam that floats docks.(closed cell polyurethane?)
Also is a pool noodle polyethelene foam? You can get that stuff in sheets and it would be nice to insulate the rhodes interior hull with.  It wont absorb water either.
Thanks,
Bob



On Feb 13, 2012, at 9:58 PM, Rob Granger <rgranger at sbc.edu> wrote:

> 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
> approach.
> 
> 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
> 
> http://building.dow.com/na/en/products/sealants/windowdoor.htm
> 
> 
> my 2 cents.
> 
> ... the other Rob
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