I am new too but I’ve been doing a lot of research concerning UV protection.
First, about the wax… the wax may stick to the part but it will wipe off since it is wax. But I don’t think the wax will stick in the way that you think because the mold should be ‘polished’ like a car so that you don’t see the wax. If not, the visible pattern (swirls and streaks) will be transferred to the part. I haven’t done this but I believe that’s how it works.
If you use UV resistant epoxy (SB112 seems to be the best and most cost effective epoxy that I can find) the part should be well protected. Supposedly people have used this with little to no change in appearance or part quality in a year’s time (or more).
By the way, UV affects the epoxy (not the CF) in two ways: The first is that it tends to discolor (yellow) the epoxy and that’s mostly a cosmetic thing. Second, it breaks down the epoxy and usually the discoloration is a sign of this. The carbon fiber itself, as far as I know, does not break down but that’s kind of irrelevant if the epoxy breaks down. With hybrids, it’s possible for the dye (if any) to fade but that shouldn’t affect the structural integrity of the part. Many people mix in carbon powder to darken the epoxy slightly, masking any discoloration.
Prepreg CF with UV resistant resin rated over 200 F is supposed to be more than ok in the sun (i.e. for marine use in constant, bright sun). Surface temperatures on CF in direct sunlight can go up that high depending on the conditions so that’s why the resin rating is important. I think using prepreg is more of a structural issue. Uniformly distributed resin leads to parts that are less apt to break down for any reason. Prepreg comes with it’s own production issues though. Probably 95% of prepregs can’t be used with polystyrene b/c of the cure temperature so you have to use something Last-A-Foam or some of the newer high tech foams… and that costs a lot. Honeycombs (nomex or even aluminum with a barrier) are also possible depending on your part .
I don’t know about the trapped gas issue. I haven’t heard of any problems other than trapped air weakens a part. I suspect it would be possible for trapped epoxy emissions or emissions from partly melted polystyrene could cause a problem but that will depend on the type of epoxy and foam that you are using.
Polystyrene will definitely deform if it’s just sitting in the sun but if it’s covered in CF, it’s somewhat insulated. If the foam does heat above the deformation temperature, it will basically shrink a bit since it’s enclosed by CF and can’t really ‘deform’. This could cause delamination. This can be limited by scoring the foam to allow the epoxy to form a deeper bond.
There is data out there but nothing that covers all combinations of CF, layup methods, epoxies, cure cycles, UV protectants, environment conditions, foam composition, etc… You’re pretty much left to try it out for yourself.
