Some Info. on Foams

Sam Finlay (
Mon, 17 May 1999 12:18:02 -0400

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West Wight Potter Website at URL
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Extruded Polystyrene: This is the same stuff I used to insulate my basement walls and floor.
15 years ago I purchased some from Agri of Virginia Inc. (540-896-7074,
Route 299 Alt Broadway, VA in 4" X 4' X 8' sheets. They no longer stock that size, but still
have it in 1&3/4" X 4' X 8' sheets ($15.19 ea.) and 2" X 2' X 8" tongue and groove ($9.79 ea.)
Agri is in the phone book under "Poultry Equipment & Supplies"; so if you've got fowl ( no pun intended)
in your neighborhood, you may be able to purchase some locally.
The stuff is really waterproof but not UV resistant. In sunlight the surface gets chalky an slowly
erodes away. The thinner sizes can be scored (deeply) w/ a razor knife and broken along the line to
cut it. Cutting w/ a hand saw is possible but the friction on the blade makes it quite a chore. A band saw
would likely make quick work of it but you'd better have a shop vac handy cause it's gonna be real messy.

Sam (hoping to eventually find time to go sailing)
P-15 Indomitable #1964
Luray, VA

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