Some Info. on Foams
Sun, 16 May 1999 12:43:45 EDT

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West Wight Potter Website at URL
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I spoke to a neighbor yesterday who is in the foam business. What he had to
say pretty much confirms what folks here on the list have observed

1) Two part polyurethane and polyisocyanate (spelling?) foams absorb more
moisture than other foams. When used in building construction it is always
sheathed and the panels are vertical - it should not be used horizontally
where water can stand on it.

2) Expanded polystyrene (EPS): This is the white stuff that picnic coolers
and diposable coffee cups are made out of. It is also the material used in my
P-15. It's made by partially filling a mold with particles of styrene, then
pressurizing the mold with steam. The particles expand into beads of foam,
filling the cavity and sticking to one another. Each individual bead has a
membrane and does not absorb water but a small amount of water can find it's
way into the voids between the beads. My neighbor says that this is not a
problem unless the temperature drops below freezing- The moisture expands
when it freezes and, driving the beads apart, weakens the block or panel.
Although my neighbor didn't mention it, do you suppose this same weakening
may also occur in saturated polyurethane?

3) Extruded Styrofoam: This is the good stuff - In construction it is used on
roofs and beneath concrete slabs. It is stronger (can support pressures of 30
psi) and has negligble moisture absorption. This is the stuff buoyancy blocks
(used in docks and houseboats) are made out of. Dow Chemical had a patent on
the process until six or eight years ago and their product is always colored
light blue. Since the patent expired, another company is making a comparable
product which is colored pink.

Hope this is of interest!

Dave Kautz
P-15 #1632 Tilly Lucy
Palo Alto, CA