Hey guys… Didn’t want to hijack that other thread so opened this. The other day I made a test panel using epoxy. After it room cured I brought it outside to see the shine and just mess around with 2000 grit to eventually see if I can polish it. Within 10 minutes it got hot in the sun and became soft and droopy. I layed it on a flat surface and it never really went back flat. I brought it in and it was all distorted, permanently. I took it outside a few days later to see what would happen and it appeared to stay in its distorted shape. It obviously postcured that first time. So it appears as if you can posture in the sun, at least to a certain point. So if the layup was in an open mold and brought out into the suns heat, would it still distort or would it remain perfectly conformed to the mold and cure harder, straight, and permanent?
The problem with bringing it out into the sun is that different spots can heat up at different rates. Depending on the shape of your part, letting it cure in the sun is alright even if it’s not bagged in your open mold, but it’s always ideal to have it bagged when post curing.
That being said, The safest way to do it is to leave it outside at sunrise while it’s still under vacuum, preferably without any shade being cast over it (which might be impossible, depending on the shape of the part).
When an epoxy part is just overnight fresh made and released from your mould they are still not fully cured so when heated up the resin goes soft again.
So it’s normal that it would temporarily go soft again and best to leave in the mould until it’s fully cured.
You also get this sort of thing when using epoxy fillers or fairing compounds, while it seems cured over night it will go soft when sanded as the friction from sanding heats it up a bit. It does not sand very well as it should so I always leave this stuff for a second day before sanding.