Hello,
I came upon an issue with some resin casts that I've not encountered.
A few days ago I made two molds to cast some small resin parts. Mold A had styrene masters in it, Mold B had some ABS/Plaster parts. I used Smooth-On MoldMax 25. The rubber cured very quick, and was developing small 'chunks' by the end of the pour. It's relatively hot and humid here.
When I de-molded the masters the next morning everything seemed fine and the molds appeared to be cured as expected, so I went ahead with casting.
I filled the molds twice, starting with SmoothCast 305. 'Mold A' produced tacky casts with glossy surfaces- two days later they're still sticky and somewhat soft. Parts from 'Mold B' don't appear to have that problem. At the same time I did these I cast a few other older molds- with similar parts in terms of thickness- and they're not tacky either, so it doesn't appear to be the resin.
I then tried a quicker cure resin, SmoothCast 300, and a slight dusting with talc. 'Mold A' didn't produce a tacky, glossy cast that time. I haven't been using talc lately since I switched to vacuum then pressure. So that is a variable.
Any ideas what might be happening here? It seems odd.
Thanks!