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Warning....when installing sound deadening material beneath the sub-floors,
think twice before using expandable foam in a can. It will expand with
considerable force in a confined area. I completed this construction four
months ago, drilled numerous holes in the floors and injected foam. In due
time, the foam expanded and found its way out through the holes as I had
expected and about a week later, I filled the holes with micro. Four months
later and much to my surprise, I found a ball of foam about six inches in
diameter on the cockpit floor. Some of the origional foam had not completely
cured and over time, it expanded with enough force to rupture a small area of
2bid tape I had applied around the sub-floor. The bottom of the fuselage had
been wet sanded to 600 grit before being turned right side up and the force of
expanding foam had produced a visual distortion in the exterior surface. It
might have been only 2 or 3 mil and about the size of a slice of tomato. Noone
else will ever see it but I know it's there and will deal with it during final painting.

Just to be safe, fill the void between sub-floor and fuselage with rigid foam,
cut to size and shape and benefit from my mistake.

Angier Ames