Carl Christianson kindly responded to my inquiry regarding the vent thing. I feel it should be pointed out (as Carl emphasizes) that when discussing “EPS” (EXPANDED Polystyrene, not EXTRUDED - “XPS”) foams, there are different densities and quality. Here is Carl’s response (used with permission from Carl) -
The following response to your email applies to <span style="text-decoration:underline"><span style="font-weight:bold">expanded</span></span> poly styrene
foam only, extruded foam of course is a different matter.
Venting Part 1
It’s probable that the air spaces that exist in a finished
6 or 7 foot blank made of quality #2 EPS, might amount to a cubic inch or two, if that much. It’s hard to image the physics required that would allow that volume
of gas to expand and contract enough to cause an issue, in regards to water
infusion or de-lamination.
With Home Depot foam, I have no idea, we do not think this foam is
suitable for surfboard construction.
In the seven years I have been making EPS blanks and surfboards, I have
seen several thousand EPS / Epoxy boards made in this area alone ( the Texas
Gulf Coast. ) There are some professional builders here that have been producing
EPS / Epoxy boards for over 10 years. These boards typically last twice as long
as polyester / urethane boards and none have ever had any " vents " installed, or
had de-laminations from lack of vents.
There has been a few de-laminations occur, but these were always traced to the use of poor quality foam that was manufactured with poor bead adhesion.
Venting Part 2
I can report that I have never seen any problems with water being "sucked in "
although these boards are ridden in water temperatures from 52 to 85 degrees.
There is some water that will flow into a ding by capillary action, 0.06 milliliters per square inch of exposed foam per hour, by test with our foam. It's evident this isn't much of an issue.
In short, if you want to produce an EPS / Epoxy surfboard of commercial quality you need:
) High quality source of EPS foam. Foam with a tool-able density that
has good adhesion between the beads.
) High quality source of Epoxy resins, specifically designed for surfboard construction.
) Proper sealing of the EPS blank . Builders here use both a 50 /50 mixtures of epoxy /microballons or spackling compounds that have microballons in them. Although both are used with success, the epoxy / microballon sealer had some additional benefits, such as increased deck strength and an epoxy to epoxy laminate bond.