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Reminds me of the time I accidentally used clear instead of hardener.  Man was that plane glossy (until you touched the surface). If it never hardens, it flows out really well.   

Master painter Bill Byles was super impressed with the gloss, but will never let me live it down. 

I tried spraying hardener on it, but no joy there.  There just isn't anything to be done but start over.

Major pain to clean up! 

If you mix epoxy with not enough hardener will it eventually harden up or will it stay gummy. I mixed up some old stuff that turned white and I think the hardener got moisture in it and so displaced some of the hardener.

Hi.
The phenomenon that you describe seems to be the partial crystallization of one of the two components.
In this case it is sufficient to heat up to about 150 ° F until the white mass is completely dissolved

Massimo

Happy day, I got the prop out and the mold cleaned up ok. The prop is rubber but I can let it sit forever and see what happens. At least it showed me I got the right amount of CF tow in the right places, that hardly ever happens on the first try. Next prop will be rock hard.

    If this is a matter of time-related changes to the material in an industrial-quality epoxy (which I certainly hope you are using, instead of a filler-laden consumer type), I would either contact the manufacturer about what to do, or replace it with fresh. TDM may well be right about heating it up and making it clear again, but I would bet you could find that heating it up to any degree exceeds the storage environmental requirements. Most modeling applications, if it looks OK and feels OK, it's probably good enough, but not for something where you have a critical safety issue like a prop.

    I also don't want to assume you *don't* already know this, but you need to follow basic engineering recommendations for composite construction of high-stress parts, and make sure you weigh out the resin and the carbon  to ensure you have the right ratio of solid to matrix for the proper strength. In most places in modeling applications, you can afford to eyeball it because it's overkill anyway, but the margins around the hub of the prop are not good and fatigue is a real factor.

    Brett

I personally would not risk using that part on a flying model, nor running it on an engine.
Seems a little risky to me.
Please be careful!

VR,
Target

I agree with the previous comments.
In my first post I suggested to heat the resin BEFORE mixing the two components.
Now I do not believe that the behavior of the product obtained is predictable.

https://www.epoxies.com/_resources/common/userfiles/file/Crystallization%20of%20Epoxy%20Resins.pdf

Massimo

The glue cured it just took longer. The prop's as hard as a rock. I just balanced it and checked the tracking, I don't see a problem.

You now have *no idea* what the engineering characteristics of the epoxy have become. Tread carefully and make sure you test it to about 15,000 rpm with abrupt plane changes, and for God's sake, stay out of line with the prop disc.

   Exactly what epoxy brand, part number, etc, are we talking about?
   
    Brett

Mix the epoxy. Apply a couple of drops on the aluminum foil. Preheat the lighter. If the majority is a solid thing - you can glue. This is not just for short epoxies.