>> Reading in my manual, it speaks of postcuring of flying surfaces
>> between 40 and 50 degrees C (104 and 122F) for 8 to 10 hours prior
>> to paint to flash off volatiles and humidity and improve strength.
>
> The manual was written for use with SP Systems Ampreg 20.
>
> Is post cure the same duration and temperature as listed in manual
> when using Aeropoxy?
>
> What components are not necessary to post cure?
>
> Thx.
> Ron Parigoris
>
Post-cure primarily affects heat-deflection temperature. Aeropoxy's
literature states that one obtains 196F-deg "HDT" with room-temp cure;
they do state that higher HDT is obtained with higher-temps in the
initial cure, but no mention of post-cure. As a practical matter, temps
pushing 200F will not be encountered in service if painted white.
SP's HDT at room-temp-cure is much less than that after 24-hours, but
---From there their literature is ambiguous as to improvement by post-cure,
or improvement merely by 28-day further cure at room temp. Ditto for
improvement in tensile strength. Shrinkage, which is advantageous to
prevent print-through, has been argued as desirable end of post-cure,
but by SP's data sheet the shrinkage is virtually zero.
No product literature I've read (SP, Aeropoxy, or West) discuss
solvent/moisture removal that may occur by elevated-temperature curing.
Nor does Burt Rutan's book mention post cure at all. I never thought
"volatiles" were a problem if the mix ratio was correct, and am less
sold on the effects of any residual moisture if cured at low humidity.
System III's "Epoxy Book" (epoxy for boat builders) discusses water vs.
epoxy an awful lot, but nothing relevant to airworthiness of airplanes,
nor even things like paint adhesion.
Another thing to consider is that if post-cure temp as low as 104F is
sufficient, such skin temps will be encountered in service. Thus it's
been argued that it will post-cure by itself.
Regards,
Fred F.
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