Good Morning Guys,
I have been starting to glass a few things on the current project and have
a coupe observations from last time til now. I used a verity of different foams
on 357Cj. The tail group was all dow foam from 1, 2, and 3 inch stock. The
wings were from 4 inch roofing insulation that was a cured foam with a skin on
each side. This foam was very similar in nature to what we commonly are
referring to as the KR foam as ordered from the kit spec's.
The Dow foam is more difficult or time consuming to shape and sand but to me
not a deal breaker. The other observation concerning this and other similar
foams (pink or some other color of this type of density) is that I feel that
the bond from glass to foam is far better. The sanding chance of damage is far
reduced by the harder density also. (scratches and dings or over sanding)
The foam that I used for 357CJ wings had resonably good bond and I just had
to use more care when sanding. The big difference here is this is the only
place that I expereinced bubbles in the glass well after the plane was
completed. A couple started showing up with inn the first 6 month's of being in
a hanger. They were pretty stable and not much change over the past 9 years
until the trip to the gathering this year. The bubbles got bigger by enough to
notice during that trip.
I installed and glassed over the first piece that I have ever used the real
KR spec'd foam. I am not real thrilled with the bond. I vacumed the foam before
I glassed and did the skim coating of micro. The foam just does not have the
ability to hold as well in my opinion for the same reason that it is easy to
sand. From looking at other KR's that I know used this foam the bubbles
(blisters may be a better term) are common.
I have also used and won't again spray foam to make fillets and bond foams
together. The fillets all blistered to some degree and when used as a bond
between 2 pieces of foam the spray foam is a denser foam and makes it difficult
to sand level. A hard ridge is form by this type of foam.
I'm saying what should be done or even that I know how I am going to continue
but just raw information to digest.
Joe Horton
Coopersburg, Pa
