Also if you do make a female mold you can fill the prop after the front
and back is glued together with syntactic foam. (Foam made by mixing micro
balloons
with epoxy). Experiment with ratios and resins to keep the viscosity down.
I don't have any strength data but I suspect it is stronger than most
of the blown foams.

A centrifugal casting arrangement might help in getting the syntactic foam
all the way out in the blade. I think this is the trick that IVO uses
but his blade design is too thin and the fiber glass skins are too thin to
develop
much torsional and bending stiffness.
Paul Lamar

I think syntactic foam is a fancy name for a paste that foams when heated.
It is only useful for prepregs.  They are also known as foaming adhesives.
I know for sure that micro/epoxy is NOT syntactic foam.

Jeff Spitzer

Not according to Composite Basics by A.C. Marshall fourth edition.
Page 3-5. Kind of the bible of composites now-a-days.

Syntactic "foam is made by mixing micro balloons and epoxy"

It might shrink slightly. 

Paul Lamar
 
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