You only let your flask set up for one hour before burn out time? That’s the first mistake in my opinion for resins. Many resin casters like to set up the flask for 2 hours minimum. You need the strongest investment you can get for resin expansion when it burns out… read on my friend…
I’ve learned how to cast jewelry from castable resins over the last few years, and boy… is it a finicky son of a %$@! but I think I have it down now.
First… you are using a good investment. Plasticast and other super high quality investments that are strong enough to survive burning out resin are ABSOLUTELY NECESSARY. You can use Plasticast but the guy who taught me how to make jewelry from resins taught me that R&R ultra vest maxx WHITE (for white gold) is actually even better and stronger than Plasticast.
The main reason resin is a pain to cast is because resin expands a little bit more right before it burns out so the investment has to be strong enough to not break up and show porosity. My guess, is that since you are using a good investment, you are either adding too much water making it weaker, or you are not doing a good, long burn out.
Do yourself a favor and start buying the Ultra Vest maxx white. This investment is so strong and can take a lot of abuse that resin expansion AND a long and hot burn out time can throw at i.
So by Ultra Vest Maxx White, then do a longer or hotter burn out time. Make sure you mix the investment perfectly. When in doubt, use a little less water.
Oh, and for resins, you should let your flask set up longer than when we do wax. 2 hours minimum. Also, you want to hold your early temperatures longer… Again, it’s the Resin expanding when it gets hot that beats the shi%$# out of your investment. So if you burn your flask out nice and slow, your Ultra Vest Max White investment will be nice and hard as nails when it starts to expand.
One last question. Are your resins being cured with ultra violet light before you get them? If castable resins are not cured properly, they never burn out or cast nice.